eSyndiCat Directory v2.3.05

Temperature Sensor Circuit

Mon, 01 Apr 2013 00:04:00 MST

The LM35 temperature sensor provides an output of 10 mV/C for every degree Celsius over 0C. At 20C the output voltage is 20 10 = 200 mV. The circuit consumes 00.

Automatic Fader Circuit

Sat, 30 Mar 2013 00:03:00 MST

In this circuit, audio fed to the control channel is amplified and rectified by Dl and D2. This dc level activates LED D3 via Q2. The light from D3 causes R9, a light-dependent resistor to decrease resistance. As Rll (audio gain) is set higher, more audio is present at the output of Ql. Audio fed into J2 is shunted to ground via R9 and less of this audio appears at J3.

Phase reversal detector

Fri, 29 Mar 2013 00:03:00 MST

Assume the correct phase sequence to be VA-VB-VC. The circuit terminals are connected such that Tl gets connected to phase A and T2 to phase B. The capacitor advances the voltage developed across R2 due to phase "B" by â€” 60Â°, while the voltages developed across it by phase "A" is in phase with VA as shown in Fig. 69-1. The net voltage developed across R2 ~ zero, the neon lamp is not energized, thereby signaling correct phase sequence. If terminal T2 gets connected to phase C, a large voltage, K(VA + Vc 60Â°), gets developed across R2, energizing the neon indicator to signal reverse phase sequence. The motor terminals can be connected to the three phases in six different combinations.

Power loss detector

Thu, 28 Mar 2013 00:03:00 MST

A positive going input charges C through the IN4148 and R. The diode keeps the scs off.

Missing pulse detector

Sun, 17 Mar 2013 00:03:00 MST

The timing cycle is continuously reset by the input pulse train. A change in frequency, or a missing pulse, allows completion of the timing cycle which causes a change in the output level. For this application, the time delay should be set to be slightly longer than the normal time between pulses

Wide-bandwidth-peak-detector

Thu, 14 Mar 2013 00:03:00 MST

This circuit can detect the positive peaks for signal frequencies higher than 5 MHz. It yields Â±1% accuracy for 400 mV to 4 V pk-pk signal amplitudes on sine, square, and triangular waveforms. The Am685 comparator output increases whenever VrN is a greater negative voltage than Vour; the high comparator output, in turn, charges C1 in a positive direction. The CA3140 op amp amplifies the C1 voltage with respect to the ECL-switching-threshold voltage ( -1.3 V) developed by diodes D1 and D2. For repetitive waveforms, each cycle boosts Vaur until it equals the peak input value. The peak-detection process is aided by the comparator"s open-emitter output, which allows C1 to charge rapidly through R2, but to discharge slowly through R2 and Rl.

High power siren

Fri, 22 Feb 2013 00:02:00 MST

ICla and IClb are wired as a slow astable multivibrator and IClc-ICld are wired as a fast astable. The output of the slow astable modulates the frequency of the fast astable, and the output of the fast astable is fed to the external speaker via the Ql VMOS power FET amplifier stage.

Precision-envelope-detector

Mon, 18 Feb 2013 00:02:00 MST

This circuit is useful for signal-processing sonar data recorded on an instrumentation-quality analog tape recorder. The envelope detector utilizes ready available parts, and furnishes accuracy beyond 100 kHz. Two LM301 op amps connected as precision absolute-value circuits use 2-pole frequency compensation for increased slew rate.

Product detector

Fri, 15 Feb 2013 00:02:00 MST

The MC1596/MC1496 makes an excellent SSB product detector. This product detector has a sensitivity of 3 microvolts and a dynamic range of 90 dB when operating at an intermediate frequency of S MHz. The detector is broadband for the entire high frequency range. For operation at very low intermediate frequencies down to 50 kHz the 0 /aF capacitors on pins 7 and 8 should be increased to 1 /aF. Also, the output filter at pin 9 can be tailored to a specific intermediate frequency and audio amplifier input impedance. The emitter resistance between pins 2 and 3 may be increased or decreased to adjust circuit gain, sensitivity, and dynamic range

Phase-detector

Fri, 08 Feb 2013 00:02:00 MST

The output of the detector contains a term related to the cosine of the phase angle. Two signals of equal frequency are applied to the inputs. The frequencies are multiplied together, producing the sum and difference frequencies. Equal frequencies cause the difference component to become de, while the undesired sum component is filtered out. The de component is related to the phase angle by the graph of Fig. 70-2B. At 90Â°, the cosine becomes zero, while being at maximum positive or maximum negative at 0Â° and 180Â°, respectively.

Undervoltage Detector

Thu, 07 Feb 2013 00:02:00 MST

The output goes high when the supply falls below a value determined by zener diode Dl. If Dl is a 5.6-V zener, the op

Detector And Controller

Tue, 05 Feb 2013 00:02:00 MST

Many applications require analog signals to be sensed and digital signals to be controlled. A way to detect these p

Sound AC switch

Mon, 04 Feb 2013 00:02:00 MST

The circuit uses a 741 op amp operating as an inverting amplifier to amplify the voltage produced by an 8-ohm speaker used to detect any sounds. The feedback resistor R3, a 1-megohm potentiometer used to vary the gain of the amplifier determines the sensitivity of the circuit. When Si is closed in the (SET)-position and a sound is applied to the speaker, SCR1 is turned on.

Thermometer For 5V Operation Circuit

Mon, 04 Feb 2013 00:02:00 MST

At the heart of this simple circuit is the well-known type KTY10 temperature sensor from Siemens. This silicon sensor is essentially a temperature-dependent resistor that is connected as one arm in a bridge circuit here. Preset PI functions to balance the bridge at 0C. At that temperature, moving coil meter Ml should not deflect, i.e., the needle is in the center position. Temperature variations cause the bridge to be unbalanced, and hencc produce a proportional indication on the meter. Calibration at, say, 20C is carried out with the aid of P2. The bridge is fed from a stabilized 5.1-V supply, based on a temperature-compensated zener-diode.

Edge-detector

Sun, 03 Feb 2013 00:02:00 MST

The 555 is a monostable that wants a negativegoing trigger. If the pulse you"re feeding it with is positive-going, you can run it through an inverter made up of either an inverting gate or, if you"re tight on space, a single transistor. Both ways are shown. The circuits shown in Fig. 25-9b are edge detectors as well, and are usually referred to as half monostables, since they can"t be used in every application.

Ir Detector

Mon, 07 Jan 2013 00:01:00 MST

Useful for checking TV remote controls, IR-based alarm systems, and IR sources, this circuit causes LED1 to turn on for two sec

Ssb/Cw Product Detectors

Sat, 05 Jan 2013 00:01:00 MST

These circuits are used for product detection of single-sidebound (SSB) and CW signals. BFO injection is typically

Balanced-modulator

Fri, 28 Dec 2012 00:12:00 MST

This circuit passes the input signal at unity gain, either unchanged or inverted, depending on the digital control input. A buffered input is shown, since low-source impedance is essential. Gain can be added by modifications to the feedback networks. Signals up to 100kHz can be handled with 20.0-V pk-pk, output. The circuit becomes a phase detector when driving the digital control input with a reference phase at the same frequency as the input signal;

Window-detector

Wed, 26 Dec 2012 00:12:00 MST

This circuit de-energizes a normally energized relay if the input voltage goes above or below two individually set voltages. The transistor driving the relay is normally turned on by R4, so the relay is normally energized. Ifthe cathode of Dl or D2 is taken negative, Ql will turn off and the relay will de-energize. The IC is a 72747 dual op amp used without feedback, so the full gain of about lOOdB is available. The amplifier output will thus swing from full positive to fullÂ· negative for a few m V change at the input.

Frequency-boundary-detector

Mon, 24 Dec 2012 00:12:00 MST

The circuit can be used to tell whether or not an input signal is within a certain frequency range. The device consists of three !Cs, a dual monostable multivibrator, and two dual D-type flip-flops. The signal whose frequency is in question is fed to the clock input of one of the flip-flops. The Q output of that flipflop (IC1a) is cross coupled to its data input so that it acts like a divide-by-two counter. The trailing edge of the Q output is used to trigger the one shots formed by IC2.

Current sensing in supply rails

Tue, 18 Dec 2012 00:12:00 MST

This capability has wide application in battery and solar-powered systems. If the ground-referred voltage output is unloaded by an amplifier, the shunt can operate with very little voltage drop across it, minimizing losses.

Phase detector with 10-bit accuracy

Mon, 10 Dec 2012 00:12:00 MST

Signals of identical frequency are applied to sync input (Pin 6) and to the demodulator input (Pin 4), respectively, the demodulator functions as a phase detector with output dc component being proportional to phase difference between the two inputs. The signals must be referenced to 0 V for dual supply operation or to VR/2 for single supply operation. At Â± 5-V supplies, the demodulator can easily handle 7-V peak-to-peak signals. The low-pass network configured with the uncommitted amplifier dc output at Pin 1 of the device.

Fast Pulse Detector Circuit

Mon, 10 Dec 2012 00:12:00 MST

A fast pulse detector can be made with this circuit. A very fast input pulse will exceed the amplifier slew rate and cause a long overload recovery time.

Phase sequence detector

Fri, 07 Dec 2012 00:12:00 MST

This circuit prevents damage to the load due to incorrect phasing. The three power SSR's are only permitted to turn-on for a phase sequence of phase A leading phase B. If phase A lags phase the input currents will cancel, causing the SCR and the inhibit SSR to remain off until the sequence is reversed.

One-chip radar detection circuit

Tue, 04 Dec 2012 00:12:00 MST

A simple X-band radar detector is capable of indicating changes in rf radiation strength at levels down to 2 mW/cm2. Radiation falling on the detector diode, produces a voltage at the input of an amplifier whose gain may be adjusted to vary the range at which the warning is given. The amplifier output drives a voltage comparator with a variable threshold set to a level that avoids false alarms. The comparator output is connected in the wired-OR configuration with the open collector output of an oscillator running at a frequency of 2 Hz.

Two-Sheets Detector

Sun, 02 Dec 2012 00:12:00 MST

Using the principle of capacitance between two plates this circuit senses when more than one sheet of paper goes betwee

Battery-powered-ground-noise-probe

Fri, 23 Nov 2012 00:11:00 MST

Oscilloscope measurements of ground noise can be unreliable because noise can enter your circuit via the scope"s three-pronged power plug. You can avoid this problem by using the ground-noise tester shown. Powered by two 9-V batteries, the circuit dissipates power only while push-to-test switch Sl is depressed. Noise pulses that reach IC2A"s switching threshold of about 1.5 to 1.8 V create a logic transition that triggers the monostable multivibrator IC3, which stretches the pulse to produce a visible blink from LED Dl.

Closed-Loop Peak Detector Circuit

Fri, 23 Nov 2012 00:11:00 MST

This closed-loop peak detector circuit uses a Schottky diode inside feedback loop to obtain good accuracy. The 20- resistance RQ isolates the 0.01- load and prevents oscillation. The dc value is read with a DVM. At a low frequency, the error is small and dominated by the decay of the detector capacitor between cycles. As the frequency rises, the error increases because capacitor charging time decreases. During this time, the overdrive becomes a very small portion of a sine-wave cycle.

Simple Full-Wave Envelope Detector Circuit

Tue, 20 Nov 2012 00:11:00 MST

Simple, yet sensitive, this amplifying full-wave detector circuit has an almost zero rectification threshold. It presents a highly linear RF load to the final IF stage.

Tracer-receiver

Thu, 15 Nov 2012 00:11:00 MST

The tracer receiver is a stereo audio amplifier/detector circuit operating near 1 kHz. Inductors Ll and 12-hand-wound coils, consisting of 200 turns of #26 wire on 2-inch ferrite cores-are tunea to the operating frequency of the amplifier/detector. The received signal strength of each individual receiver is indicated by an LED. The audio output of the receiver is fed to a stereo headphone. That dual-receiver scheme helps in locating and tracking the hidden wire or cable by giving a directional output that indicates the cable"s path.

Peak detector II

Fri, 09 Nov 2012 00:11:00 MST

If subsequent input voltage exceeds that stored in Cl, the comparator voltage will go high and charge Cl to new higher peak voltage.

Angle of rotation detector

Thu, 08 Nov 2012 00:11:00 MST

The figure shows two TL3103 linear Hall-effect devices used for detecting the angle of rotation. The TL3103s are centered in the gap of a U-shaped permanent magnet. The angle that the south pole makes with the chip face of unit #1 is defined as angle 0. Angle 0 is set to 0Â° when the chip face of unit #1 is perpendicular to the south pole of the magnet. As the south pole of the magnet sweeps through a 0Â° to 90Â° angle, the output of the sensor increases from 0Â°.

Open-Loop Peak Detector Circuit

Fri, 05 Oct 2012 00:10:00 MST

In this open-loop design, the detector diode is Dl, and a level shifting or compensating diode is D2. Load resistor RL is connected to -5 V, and an identical bias resistor RL is connected to -5 V, and identical bias resistor RB is used to bias the compensating diode. Resistors with equal values ensure that the diode drops are equal. Low values of RL and RB (1 kU to 10 kf2) provide fast response, but at the expense of poor low-frequency accuracy. High values of RL and Rn provide good low-frequency accuracy, but cause the amplifier to slew rate limit, resulting in poor high-frequency accuracy.

Peak Detector

Tue, 02 Oct 2012 00:10:00 MST

A 0-to-5 V input drives the negative input of LM392 comparator if reset (pin 12) if DC4060BE is pulled high then low, all out

Frequency limit detector

Mon, 01 Oct 2012 00:10:00 MST

Simple frequency limit detectors providing a GO/NO-GO output for use with varying amplitude input signals may be conveniently implemented with the ICL8211/8212. In the application shown, the first ICL8212 is used as a zero-crossing detector. The output circuit consisting of R3, R4 and C2 results in a slow output positive ramp. The negative range is much faster than the positive range. R5 and Rg provide hysteresis so that under all circumstances the second ICL8212 is turned on for sufficient time to discharge C3. The time constant of R7C3 is much greater than R4C2. Depending upon the desired output polarities for low and high input frequencies, either an ICL8211 or an ICL8212 may be used as the output driver.

True rms detector

Wed, 19 Sep 2012 00:09:00 MST

The circuit will provide a dc output equal to the rms value of the input. Accuracy is typically 2% for a 20 Vpp input signal from 50 Hz to 100 kHz, although it"s usable to about 500 kHz. The lower frequency is limited by the size of the filter capacitor

Out-of-bounds-pulse-width-detector

Tue, 18 Sep 2012 00:09:00 MST

Requiring only two ICs to monitor a train of positive pulses, this circuit produces a single positive output pulse for each input pulse whose duration is either too long or too short. You specify the minimum and maximum limits by adjusting the trimming potentiometers, R1 aod R2. You cao set the value of the acceptable pulse width from approximately 50 ns to 10 f-!S, for a 74123 monostable multivibrator. The leading edge of ao input pulse triggers one shots IClA and IClB as you cao see from the timing diagram.

Proximity alarm

Mon, 17 Sep 2012 00:09:00 MST

Inverters Ula and Ulb are connected in a simple RC oscillator circuit. The frequency is determined by the values of Rl, Cl, C2; and the internal characteristics of the integrated circuit. As long as the circuit is oscillating, a positive dc voltage is developed at the output of the voltage-coupler circuit: C3, Dl, D2 and C4. The dc voltage is applied to the input of Ulcâ€”the third inverter amplifierâ€”keeping its output in a low state, which keeps Ql turned off so that no sound is produced by BZ1. With Cl and C2 adjusted to the most sensitive point, the pickup plate will detect a hand 3 to_5-inches away and sound an alert.

Sleep Mode Circuit Circuit

Mon, 10 Sep 2012 00:09:00 MST

The HA7210 oscillator 10 combines with an IOL7642 quad CMOS op amp to produce a sleep-mode control circuit. The circuit is put into the sleep mode with a logic high applied to the Reset input or with an RC timer for automatic reset.

Pulse coincidence detector

Thu, 06 Sep 2012 00:09:00 MST

Unless inputs A and (2- to 3-V amplitude) occur simultaneously no voltage exists across Rl. Less than 1 microsecond overlap is sufficient to trigger the scs.

High frequency peak detector

Fri, 31 Aug 2012 00:08:00 MST

National Semiconductor's DP8464B is primarily intended for use in disk systems as a pulse detector. However it can be easily used as a general purpose peak detector for analogue signals up to 5 MHz. The chip can handle signals between 20 and 66 mV peak-to-peak. The circuit includes a filter with constant group delay characteristics to band limit the signal. Typically the -3 dB point for this filter will be at about 1.5 times the highest frequency of interest.

Duty-Cycle Detector

Mon, 27 Aug 2012 00:08:00 MST

This circuit looks at the time an incoming pulse is high. If the incoming pulse is shorter than the adjusted (VAR1) pul

Sound Sensor

Wed, 25 Jul 2012 00:07:00 MST

By using a microphone, high-gain amplifier (Fig. 37-10(b)), and detector-relay driver (Fig. 37-10(a)) a sound-detecting alarm

Hook Sensor Loop Circuit

Mon, 23 Jul 2012 00:07:00 MST

Here`s an effective for a temperature sensor to receive power from a 4-to-20 mA loop without actually affecting the loop current (see the figure). This particular temperature sensor IC (AD590F) conducts 1 / when powered by a supply in the range of 4 V to 40 Vdc. The scheme uses a 5-V Zener diode (Dl) to regulate the power source for AD590F. Most of the current flows through the Zener diode and a small current flows through AD590F.

Missing-pulse-detector

Sun, 08 Jul 2012 00:07:00 MST

This circuit will detect a missing pulse or abnormally long spacing between consecutive pulses in a train of pulses. The timer is connected in the monostable mode. The time delay should be set slightly longer than the timing of the input pulses. The timing interval of the monostable circuit is continuously retriggered by the input pulse train, 1-J. The pulse spacing is less than the timing interval, which prevents Vc from rising high enough to end the timing cycle. A longer pulse spacing, a missing pulse, or a terminated pulse train will permit the timing interval to be completed.

Infrared approach detector / sensor

Fri, 06 Jul 2012 00:07:00 MST

Basic operation of the monitor attached to the circuit is to detect objects (obstacles), at distances ranging from a few millimeters to and a few centimeters. Depending circuits used in industry and hospitals. The position sensor IC2 optoapomonotis used a type of Siemens SFH900 someone similar. The sign shows, led to a phase locked circuit (contained in IC1), which compares with signal frequency an oscillator which is also located within the same chip. For as long as the frequencies of two signals coincide, the pin output of IC1 (pin 8) is still reasonable 'O'.

Ic Product Detectors

Thu, 05 Jul 2012 00:07:00 MST

These product detectors use IC devices. SSB and CW signals can be detected with them. The circuits should be useful up

Simple-window-detector

Wed, 04 Jul 2012 00:07:00 MST

This simple window detector uses only half of a 7400 quad NAND gate plus four resistors, chosen so that the voltage at point A exc.,eds the voltage at point B for any input voltage. With no input applied or when VIN is at ground, the output of gate Gl is one; hence G2"s output is also one. As the input voltage increases, VA rises faster than JOB.

Zero-crossing detector

Fri, 29 Jun 2012 00:06:00 MST

This zero-crossing detector uses a dual LM393 comparator, and easily controls hysteresis by the reference levels which are set on the comparator inputs. The circuit illustrated is powered by +10-V power supplies. The input signal can be an ac signal level up to + 8 V. The output will be a positive going pulse of about 4*4 V at the zero-crossover point. These parameters are compatible with TTL logic levels. The input signal is simultaneously applied to the non-inverting input of comparator A and the inverting input of comparator B. The inverting input of comparator A has a +10 mV reference with respect to ground, while the non-inverting input of comparator has a -10 mV reference with respect to ground.

Double-ended limit detector

Fri, 29 Jun 2012 00:06:00 MST

Detector uses three sections of an L144 and a CMOS NAND gate to make a very low power voltage monitor. The 1 MO resistors Rl, R2, R3, and R4 translate the bipolar Â±10 V swing of the op amps to a 0 to 10 V swing acceptable to the ground-referenced CMOS logic

Digital-frequency-window

Sun, 17 Jun 2012 00:06:00 MST

This circuit detects frequency variation above or below preset limits. IC1 is a binary counter docked at FcLKÂ· The outputs are comparea with switch preset values by IC2 and IC3. The input signal, which must be a positive-going pulse, is used to reset IC1. The P greater than Q output of the comparators is at logic 0 for input frequencies below the preset values. Above the preset count, a pulse train is output.

Edge detector

Wed, 13 Jun 2012 00:06:00 MST

This circuit provides a short negative-going output pulse for every positive-going edge at the input. The input waveform is coupled to the input by capacitor C; the pulse length depends, as before, on R and C

Precision-threshold-detector

Wed, 13 Jun 2012 00:06:00 MST

This circuit requires low noise, low and stable offset voltages, high open loop gain, and high speed. These requirements are met by the HA514 7. The standard variations of this circuit can easily be implemented using the HA-5147. For example, hysteresis can be generated by adding R1 to provide small amounts of positive feedback.

Zero crossing detector

Sat, 02 Jun 2012 00:06:00 MST

This detector is useful in sine wave squaring circuits and A/D converters. The positive input may either be grounded or con-output nected a nulling voltage which cancels input offsets and enables accuracy to within microvolts of ground

Noaa Weather Alert Decoder

Wed, 30 May 2012 00:05:00 MST

This circuit detects the 1050-Hz tone sent by the NOAA (National Oceanic and Atmospheric Administration) Weather

Digital-peak-detector

Thu, 24 May 2012 00:05:00 MST

The peak detector tracks and holds, using the charge-storing ability of a capacitor, the highest output voltage from a transducer. Initially, the voltage on the inverting input of the comparator is at ground level. As a small voltage (0-5 V) is captured by the peak detector and presented to the comparator"s noninvertÂ· ing input, the output will swing high, which asserts the bilateral switch; clock pulses now pass through the switch to clock both the BCD and binary counters. The outputs of the binary counters are connected to an R2R ladder network, which functions as a digital-to-analog converter.

Null-detector

Tue, 22 May 2012 00:05:00 MST

In this indicating comparator circuit, R2 sets the hysteresis. If the 741 saturates at Â± 12 V, the current in R1 will be approximately Â± 10 mA if 0.1 V hysteresis is desired.

Data Line Remote Short Sensor

Wed, 16 May 2012 00:05:00 MST

Sensing short circuits in equipment that performs under water is especially critical, but Fig. 20-4"s wet-mat

Capacitive-sensor-alarm

Wed, 09 May 2012 00:05:00 MST

The unit is constructed around a balanced-bridge circuit. using both capacitance and inductance. The bridge consists of capacitors C2 and C3, and the center-tapped winding of Tl. One end of the bridge is coupled to ground by C4, while capacitance changes are introduced through Cl. A small capacitance change unbalances the bridge and produces an ac signal at the base of Ql. Transistors Q1 and Q2 are connected to form a modified-Darlington amplifier.

Window-detector

Thu, 03 May 2012 00:05:00 MST

This novel window detector uses only two op amps.

Phase-sequence detector II

Thu, 26 Apr 2012 00:04:00 MST

This circuit derives its supply voltage, Vcc and Vdd from <Â£c. This factor, together with the neon lamps and zener diodes in the phase inputs, establishes 50% threshold that detects low voltage or absence of one or more phases.

Pulse sequence detector

Wed, 25 Apr 2012 00:04:00 MST

The resistor divider connected between Ql and Q2 supplies IH to Ql after input A triggers it. It also prevents input from triggering Q2 until Ql conducts.

Sonic Kaleidoscope Circuit

Wed, 25 Apr 2012 00:04:00 MST

The microphone input, MIC1, is fed through C3 and R4 to inverting amplifier U2-a; the gain of U2-a is controlled by potentiometer R5. The output of U2-a is fed through C4 to the remaining op-amps (U2-b, U2-c, U2-d), which are all configured as band-pass.filters. Each filter is tuned to pass a different range of frequencies by its resistor/capacitor combination. With the values shown, U2-b, U2-c, and U2-d have center frequencies of roughly 100, 1000 and 1500 Hz, respectively. Resistors R6, R9, R12 control the bandwidth and gain of their respective filter circuits, and can range in value from 10 to 15 kO. The output of U2-b is capacitively coupled via Cl 1 to the input of U3, with R15 serving as the load resistor for U2-b.

Window-detector

Mon, 23 Apr 2012 00:04:00 MST

The detector circuit compares the output voltage of two separate voltage dividers with a fixed reference voltage.

Peak detector

Thu, 12 Apr 2012 00:04:00 MST

Circuits are easily implemented using the CA3130 BiMOS op amp. For large-signal inputs the bandwidth of the peak-negative circuit is less than that of the peak-positive circuit.

peak detector

Sun, 08 Apr 2012 00:04:00 MST

The purpose of the circuit is to hold the peak of the input voltage on capacitor Cl, and read the value, V0, at the output of U2. Op amps Ul and U2 are connected as voltage followers. When a signal is applied to Vj, Cl will charge to this same voltage through diode Dl. This positive peak voltage on Cl will maintain V0 at this level until the capacitor is reset (shorted). Of course, higher positive peaks will raise this level while lower power peaks will be ignored. Cl can be reset manually with a switch, or electronically with an FET that is normally off.

Peak Detector

Fri, 06 Apr 2012 00:04:00 MST

An analog signal requires about 100 ns to propagate through the HA-5320. For time-varying signals, this assures a voltage dif

Low-drift-peak-detector

Wed, 04 Apr 2012 00:04:00 MST

This circuit uses op amp Ul to compensate for the offset in peak detector diode Dl. Across c. is the exact peak voltage;

Tone detector

Sun, 01 Apr 2012 00:04:00 MST

The detector circuit is made up a two-amplifier multiple feedback bandpass filter followed by an ac-to-dc detector section and a Schmitt Trigger. The bandpass filter (with a Q of greater than 100) passes only 5Q0 Hz inputs whch are in turn rectified by Dl and filtered by R9 and Ca

Shock-sensor circuit prevents data corruption

Sun, 31 Mar 2013 00:03:00 MST

Hard-disk drives for laptop and other portable applications need to withstand significant g-force shocks when operating. A typical 1.8-in. drive writes servo information over less than 15% of the disk`s active area, which means that the read/write head spends more than 85% of the time outside the servo loop`s control. A g-force shock during this time could cause the read/write arm and head to move away from the current write track and to permanently write corrupting data on an adjacent track or elsewhere.

Human Traffic Footstep Alarm

Thu, 28 Mar 2013 00:03:00 MST

This circuit processes the amplified signals from the footstep detector circuit and activates a microprocessor when the circuit detects footsteps. At has an adjustable sensitivity.

UL GROUND RESISTANCE TESTER

Wed, 27 Mar 2013 00:03:00 MST

UL requires that an electrical system using a metal chassis earth ground connection have a resistance of less than 0.1 ohms. This resistance must be tested with actual line current in excess or 10 amps. The circuit shown uses a couple of LEDs to indicate if in fact the resistance is less than 0.1 ohms. It uses a modified transformer to produce a 2.5vac output with at least 10 amps of supply current.

Pump Motor Monitor

Tue, 26 Mar 2013 00:03:00 MST

This circuit can turn on a light or sound a beeper, whenever an AC line powered pump motor turns on. It is designed to detect the motor current using a small inductor placed on the outside of the motors power cable. No direct wire contact is needed.

disco lighting

Tue, 26 Mar 2013 00:03:00 MST

This project is intended for controlling mains powered disco lighting, although there are many other possible uses for controlling almost any mains appliance. It will control five seperate channels at up to 3 Amp per channel. This could be increased by designing another PCB with wider tracks than the PCB included with this design. I could have used relays to control my lights, but triacs seemed like a more sensible solution as they react quicker and are totally silent as they contain no mechanical parts.

Home Made Geophone Detects Foot Stomp

Mon, 25 Mar 2013 00:03:00 MST

A home made geophone is made from a strong magnet, a coil of wire and a rubber band. The circuit is sensitive enough to detect the vibrations of a nearby foot stomp. It could be used as an earthquake detector.

Home Made Geophone Detects Foot Stomp

Mon, 18 Mar 2013 00:03:00 MST

Ultrasonic / Bat detector

Mon, 18 Mar 2013 00:03:00 MST

I have found this circuit to have better sensitivity, both in distance to a visible bat and in audio frequency, than some other published circuits using a 40kHz transducer with 4000x gain amplification, though the 40kHz transducer I used for the comparison may have a bearing on these results. The high-pass filter is included purely to help eliminate the circuit being triggered by ambient noise. The filter is a 4-pole Chebychev with a very steep roll-off below 15kHz. There is virtually zero response at 10kHz and below. This type of circuit relies on the wanted signal being loud enough to trigger the CMOS counter, so the less unwanted signal that reaches the circuit the better.

Magnetic proximity sensors

Mon, 11 Mar 2013 00:03:00 MST

Here is an interesting circuit for a magnetic proximity switch which can be used in various applications. The magnetic proximity switch circuit, in principle, consists of a reed switch at its heart. When a magnet is brought in the vicinity of the sensor (reed switch), it operates and controls the rest of the switching circuit. In place of the reed switch, one may, as well, use a general-purpose electromagnetic reed relay (by making use of the reed switch contacts) as the sensor, if required.

Mounting Considerations for ADXL Series Accelerometers

Sun, 10 Mar 2013 00:03:00 MST

As with all accelerometers, optimum performance depends on proper mounting of the device. It must be mounted so that the sensor is properly coupled to the object for which acceleration is to be measured. Also the effects of mechanical resonances must be minimized.

Dew sensor circuit

Sat, 09 Mar 2013 00:03:00 MST

Dew (condensed moisture) ad- versely affects the normal per- formance of sensitive electronic devices. A low-cost circuit described here can be used to switch off any gadget automatically in case of excessive humidity. At the heart of the circuit is an inexpensive (resistor type) dew sensor element. Although dew sensor elements are widely used in video cassette players and recorders, these may not be easily available in local market. However, the same can be procured from authorised service centres of reputed companies. The author used the dew sensor for FUNAI VCP model No. V.I.P. 3000A (Part No: 6808-08-04, reference no. 336) in his prototype.

Fan Failure Detector circuit

Wed, 06 Mar 2013 00:03:00 MST

The cooling is not only a PC using a small fan with an electronic commutator [1]. A special feature of these fans is that their removal is less dependent on the load. Indicators monitoring the DC component of current may therefore be very reliable. Interesting connection indicator I found in Electronic Design magazine [2]. The indicator in Figure 1, the only change in passing current. Measured current waveform is the fan in Figure 2 The voltage at the base of the transistor is filtered by resistor R1 and capacitor C1. The immediate changes in the supply current (during the fall) opens the transistor and discharges the capacitor C2.

Acceleration to Frequency Circuits

Mon, 04 Mar 2013 00:03:00 MST

Low cost monolithic accelerometers may be paired with a circuit whose output changes with frequency (V/F) to provide a TTL level frequency output. A microprocessor can be easily programmed to read this signal and directly compute the applied acceleration, and the output of a V/F circuit can be sent down a long transmission line and still be reliably recovered at the other end.

current-sensing instrumentation amplifier

Sun, 03 Mar 2013 00:03:00 MST

High-speed current sensing presents a designer with some significant challenges. Most techniques for sensing current involve measuring the differential voltage the current produces as it flows through a sense element, such as a resistor or a Hall-effect device. The differential voltage across the sense element is generally small and is often riding on a common-mode voltage that is considerably larger than the differential voltage itself.

Practical UltraSonic Radar

Sat, 02 Mar 2013 00:03:00 MST

This is a very interesting project with many practical applications in security and alarm systems for homes, shops and cars. It consists of a set of ultrasonic receiver and transmitter which operate at the same frequency. When something moves in the area covered by the circuit the circuit�s fine balance is disturbed and the alarm is triggered. The circuit is very sensitive and can be adjusted to reset itself automatically or to stay triggered till it is reset manually after an alarm.

Auto Stud Sensor

Sat, 02 Mar 2013 00:03:00 MST

This thing is a very nifty capacitive sensor. For you europeans, this little gem is used in north america mostly for detecting wooden beams behind drywall or plaster. I`ll take one of these over the new design any day, because these ones don`t error out every time you try to use them in a non-standard way.

Measure open-circuited cables using a multimeter

Fri, 01 Mar 2013 00:03:00 MST

You can use a multimeter with capacitance-measurement capability to measure the length of wire or cable to an open circuit. The capacitance of a pair of wires (or a wire to a shield) is directly proportional to the length of the wire. If you know the capacitance per foot of wire, then you can calculate how far it is to the open circuit.

Circuit senses high-side current

Thu, 28 Feb 2013 00:02:00 MST

The accurate, high-side, current-sense circuit in Figure 1 does not use a dedicated, isolated supply voltage, as some schemes do. Only the selected transistors limit the common-mode range. The circuit measures the voltage across a small current-sense resistor, RS. The operation of the circuit revolves around the high-side current mirror comprising Q1 and Q2. All the circuit components have one overall function: to make the collector currents equal in Q1 and Q2.

Wireless Auto Tachometer

Tue, 26 Feb 2013 00:02:00 MST

Anyone performing their own automobile tune-ups knows how important it is to know your engines speed. With this tachometer, you can measure your engines speed without any connections or annoying timing lights.

Infra-red Level Detector

Sun, 24 Feb 2013 00:02:00 MST

This circuit is useful in liquids level or proximity detection. It operates detecting the distance from the target by reflection of an infra-red beam. It can safely detect the level of a liquid in a tank without any contact with the liquid itself. The device`s range can be set from a couple of cm. to about 50 cm. by means of a trimmer. Range can vary, depending on infra-red transmitting and receiving LEDs used and is mostly affected by the color of the reflecting surface. Black surfaces lower greatly the device`s sensitivity.

Color Sensor circuit

Sun, 24 Feb 2013 00:02:00 MST

Colour sensor is an interesting project for hobbyists. The cir- cuit can sense eight colours, i.e. blue, green and red (primary colours); magenta, yellow and cyan (secondary colours); and black and white. The circuit is based on the fundamentals of optics and digital electronics. The object whose colour is required to be detected should be placed in front of the system. The light rays reflected from the object will fall on the three convex lenses which are fixed in front of the three LDRs. The convex lenses are used to converge light rays. This helps to increase the sensitivity of LDRs. Blue, green and red glass plates (filters) are fixed in front of LDR1, LDR2 and LDR3 respectively. When reflected light rays from the object fall on the gadget, the coloured filter glass plates determine which of the LDRs would get triggered.

High-side current sensor monitors negative rail

Wed, 20 Feb 2013 00:02:00 MST

All dedicated current-sense amplifiers provide high-side sensing on a positive supply, but you can adapt such circuits for monitoring a negative supply (Figure 1). The positive-supply pin, V+, connects to the system`s positive supply, and the ground pin, GND, connects to the negative supply, VEE. That arrangement monitors the negative supply and provides a positive output voltage for the external interfacetypically, an A/D converter.

high-side current sensing

Thu, 07 Feb 2013 00:02:00 MST

White LEDs find wide use in backlighting color-LCD screens in most portable devices, such as cellular phones, PDAs, and MP3 players. Multiple LEDs often connect in series to ensure that the same current flows through every LED. To forward-bias these LEDs, a voltage of 10 to 16V comes from an inductor-based boost regulator, such as an SP6690. However, white LEDs are behind the display, whereas boost regulators are on the main pc board, and it is important to minimize the number of interconnects.

Versatile digital speedometer uses few components

Wed, 06 Feb 2013 00:02:00 MST

A speedometer measures a wheel`s rotational speed. Unlike conventional mechanical and moving-magnet designs that use analog moving-pointer displays, the electronic speedometer in this Design Idea features a digital readout and a power-saving device that uses few components. Figure 1 shows the digital speedometer`s circuit design. An Atmel AVR AT90S2313 microcontroller, IC1, drives IC3, a 16-character, two-row LCD.

MAGNETIC LEVITATION DEVICE

Mon, 04 Feb 2013 00:02:00 MST

Here`s the schematic of the device depicted in the photo. Each of the ten coil-assemblies has its own copy of the above circuit. The SS41 is a Microswitch Hall Effect magnetic field sensor IC that I found in Surplus catalog for $.50 each. Any similar hall IC should work, as long as it is fairly sensitive and is magnetically bipolar. All Electronics currently has one for $.50, HESW-5, but it is a surface-mount package with tiny, hard-to-solder leads. The professional supplier for hall-effect devices is Allegro Micro.

Voltage reference improves JFET

Sun, 03 Feb 2013 00:02:00 MST

The common JFET current-source in Figure 1a has average output impedance and depends heavily on the JFET`s VP and IDSS variations. These manufacturing variations limit the initial accuracy of the current setpoint that the circuit can obtain with a fixed R1. Most users of JFET current-sources sample VP and IDSS for each lot of JFETs and then select R1 by first solving the quadratic equation ID=IDSS(1VGS/VP)2 for VGS and then solving the current-setpoint equation ISOURCE=VGS/R1.

Use RS-232C port to measure pressure

Sat, 02 Feb 2013 00:02:00 MST

A simple circuit (Figure 1) and accompanying software turn a pressure sensor into an accurate and cheap pressure digitizer that works with any PC`s RS-232C COM port. Many manufacturers make micromachined silicon piezoresistive pressure sensors. Sensors are available with full-scale sensitivities ranging from inches of water to hundreds of pounds per square inch.

Earthquake Sensor/Alarm

Sat, 02 Feb 2013 00:02:00 MST

Here is a simple sensor which can detect the seismic vibrations caused by a person or large animal walking nearby. A representative application for the sensor is a deer repellent for the vegetable garden. When a deer steps near the sensor a loud buzzer or beeper sounds for a few seconds startling the would-be vegetable thief away. The sensor also makes an effective intruder detector to catch trespassers as soon as they step on the property!

Circuit measures currents in dc servo motor

Sat, 26 Jan 2013 00:01:00 MST

The simple circuit design in Figure 1 lets you measure all components of a current flowing in a dc servo motor. The rectified output of the circuit uses ground as a reference, so you can measure the output by using a single-ended A/D converter. The current-sense resistor, R1, has a value of 0.1. The Zetex (www.zetex.com) ZXCT1010 IC converts the differential signal across R1 to a single-ended signal. Two of these ICs form a signal rectifier.

Magnetic Proximity Switch

Tue, 22 Jan 2013 00:01:00 MST

There is practically no house without an overhead tank (OHT). People who use electrically-operated water pumps for filling the OHT find it very inconvenient to switch off the pump when their overhead tank starts overflowing, specially when they are busy. So there is plenty of water wastage as well as wastage of power (consumed by the pump). However, there is a solution to get rid of this headache.

Accelerometer Scale Factor and Offset Adjustments

Thu, 17 Jan 2013 00:01:00 MST

The ADXL50 and ADXL05 accelerometers are small, low cost, easy to use devices. These modern integrated circuits have an onboard buffer amplifier that allows the user to change the output scale factor and 0 g bias level.

Capacitance Meter III

Mon, 14 Jan 2013 00:01:00 MST

This simple add-on capacitance meter has been specially designed to help you identify capacitors from 1p to 10u. There has always been a problem identifying capacitors, due to the enormous variety in size, shape and coding. Most of the time it is impossible to identify them by size due to the different forms of construction. So you have to be able to read and interpret the codes on the body. But if the numbers are missing or microscopic in size, you have a problem. The only solution is to have a piece of test equipment to identify them for you.

Car lamp failure detector

Sat, 12 Jan 2013 00:01:00 MST

In Fig.1 see a DC current ? sensing switch, in which the current is applied from an 8 to 16 Volt supply. The R1 value is chosen so that it generates roughly 100 mV at the required trip current. In Fig. 2 shows how the above circuit can be made to act as a car lamp ? failure switch which turns on if any of the monitored lamps burn out. R is wired in series with the wiring harness feed to a selected ??cluster? of up to four similarly rated lamps.

Current-sense amplifier handles high voltages

Mon, 07 Jan 2013 00:01:00 MST

High-side current-sense amplifiers, such as IC1 in Figure 1, monitor current from a battery or dc power line in systems for which the ground-return continuity is crucial. IC1`s 36V maximum operating voltage, however, excludes some applications, including traction-motor batteries and central-exchange power supplies, both of which require operation at voltages exceeding 72V.

Magnetic Gun

Sat, 05 Jan 2013 00:01:00 MST

IC1 is a 555 timer in astable mode, sending approx. 10 ms pulses to decade counter IC2. IC2 is continually reset through R3, until pin 15 is taken low through the "Fire" button. IC2 then sequences through outputs Q1 to Q7, to feed power transistors TR1 to TR4, which fire electromagnets L1 to L4 in rapid sequence.

Power-Saving Pedometer Also Measures Speed

Thu, 03 Jan 2013 00:01:00 MST

A pedometer is a device that counts the number of steps taken by a person and calculates the distance traveled by multiplying the number of steps by the length of the step. Here`s a design solution for building a pedometer using the AVR MCU. The circuit not only combines all of the features of the traditional pedometer, it saves power (low power consumption is a must for a portable device) as well. The design also includes instantaneous speed measurement.

Digital position encoder does away with ADC

Mon, 31 Dec 2012 00:12:00 MST

The position encoder in Figure 1 is a simple yet powerful circuit that converts the change in resistance of a potentiometer into a digital value without using an expensive A/D converter. The working principle is a resistance-to-PWM converter built around the common 555 timer IC. A change in the potentiometer`s resistance causes a proportional change in the duty cycle of the timer`s output, which essentially encodes the resistance values as a PWM signal.

Radio Wave Alarm

Thu, 27 Dec 2012 00:12:00 MST

This simple circuit is sure to have the police beating a path to your door - however, it has the added advantage of alerting you to their presence even before their footsteps fall on the doormat. The circuit transmits on Medium Wave (this is the small problem with the police). IC1a, together with a sensor (try a 20cm x 20cm sheet of tin foil) oscillates at just over 1MHz. This is modulated by an audio frequency (a continuous beep) produced by IC1b.

Geomagnetic Field Detector circuit

Wed, 26 Dec 2012 00:12:00 MST

This basic oscillator will detect the Earth magnetic field. The ferrite rod and coil are taken from an old Medium Wave receiver and a small magnet is glued at one end. Tune to a medium wave commercial station until you hear a beat note. Any movement of the ferrite rod will produce an audible note that depends on the prevailing Earth magnetic field. Screening is essential. Use a plastic box padded, on the inside, with copper wires running parallel to the rod and grounded in one place only. A small hole is made in the box in order to adjust the trimmer capacitor with a plastic screwdriver. An American equivalent to the BC337 could be the 2N2369A but I did not try it out.

Position detectors provide motor-control logic

Mon, 24 Dec 2012 00:12:00 MST

In the circuit of Figure 1, assume that a brush-type dc motor must drive a load back and forth between two endpoints on a lead screw. Optical sensors determine end of travel, and an SPDT switch selects to which end to send the load. The sensors themselves supply all the necessary directional logic, and a triac powers the motor with the necessary polarity of half-wave pulses from the 13.5V-ac input.

Peak Level Indicator

Sun, 23 Dec 2012 00:12:00 MST

This circuit was designed to provide a valuable test equipment tool for sound reinforcement systems like guitar amplifiers and the like. Used in conjunction with a signal generator it can be of considerable help in setting and controlling levels through any amplifying chain.

Signal and Tone Activated Relay Switch

Fri, 14 Dec 2012 00:12:00 MST

In the Fig.1, exist a circuit, which is a sensitive switch that corresponds in AC signals of input, for signals above 5mV. Corresponds in all the signals from 50 HZ until 3KHZ, region in which found the human voice. The RV1 is regulated so much what RL1 it?s in situation OFF, when the input is it has null signal. In the Fig.2, exist a band - pass filter, coordinated in the 1KHZ, which can be placed in line in the bronchus of negative feedback, in points A, B, C, making sensitive the circuit only in this frequency.

Hand Clap Lamp Control

Wed, 12 Dec 2012 00:12:00 MST

What a way to drive a triac! This was a mass-produced consumer item so I guess it must be OK though.

HONEYBEE COUNTER

Mon, 03 Dec 2012 00:12:00 MST

I designed a circuit similar to this one a long time ago to help a beekeeper count the number of bees going into or out of a hive. The low power circuit uses a slotted opto-sensor to detect the passing bees. The circuit advances an electronic counting module whenever a honeybee passes through the sensor. The device only counts the number of bees going through the sensor. A different circuit would be needed to count the number of bees only going out or only coming into the hive.

Fast Audio Peak Limiter

Sun, 02 Dec 2012 00:12:00 MST

The circuit devised by Phil Allison still has some input voltage limitations, since it is based on a FET. Junction FET VCAs also create considerable distortion, with the worst of it appearing when the signal is attenuated by 6dB. The common way to fix this problem is to apply 1/2 of the drain voltage to the gate, along with the control voltage. Figure 1 shows the conventional way this is done. The predominantly second harmonic distortion is converted by this technique, to become a very much reduced amount of third harmonic distortion.

Electrical Current Indicator

Thu, 29 Nov 2012 00:11:00 MST

I designed this circuit as a simple current indicator for any load ranging from 40 watts to 250 watts. The circuit turns on a small LED, whenever it detects current flowing to a remote load.

High-isolation converters use off-the-shelf magnetics

Wed, 28 Nov 2012 00:11:00 MST

Isolated flyback converters usually evoke thoughts-or bitter memories-of custom transformers, slipped delivery schedules, and agency-approval problems. Off-the-shelf flyback transformers carry isolation ratings of only 300 to 500V and rarely of as much as 1 kV. Gate-drive transformers are readily available from stock with high isolation ratings and low cost, but they are wound on ungapped cores, have high inductance (500 µH to 2 mH), and quickly saturate in a normal flyback-converter circuit.

MACHINE VIBRATION TRIGGERS HOUR METER

Tue, 27 Nov 2012 00:11:00 MST

This circuit allows an off-the-shelf battery powered digital hour meter to be turned on and off, according to a machine`s operation, without requiring a direct electrical connection to the machine. Machine vibrations are detected by an off-the-shelf piezoelectric wafer. The wafer is normally used as a sound generator. The 3v power could be tapped from the hour meter`s own lithium battery or from a separate 3v lithium battery. The circuit only draws about 1.5uA, so a 250mA-hr battery would power the circuit for about 10 years.

InfraRed Detector (PIC12F629)

Mon, 26 Nov 2012 00:11:00 MST

This unit uses one TSAL6100 IR/LED emitter from Digi-Key. This IR diode has a narrow (10 degree) radiation pattern at 940 NM. It is driven via 2n2904 transistor for maximum current pulses. The detector is a Vishay TSOP4838 38Khz integrated receiver module. The 38Khz signal for the emitter is generated in software. Here is the idea: Send out a 38Khz IR signal and look for its reflection off a nearby object. Both the emitter and detector are optically and electrically isolated from each other to minimize self actuation. Additionally, the pulses are sent out only at certain intervals and the PIC only looks for the signal at the end of the output burst.

IR distance ranger covers 1 to 20 cm

Mon, 19 Nov 2012 00:11:00 MST

Commercially available IR distance rangers typically handle a 3- to 30-in. detection distance. Many times, it is necessary to determine smaller distances. The circuit in Figure 1 is useful for measuring small distances to reflective surfaces. Its measurement range is from less than 1 cm to approximately 20 cm for a flat, white surface. The output of the circuit is an active-high pulse at connector P1.

High-voltage current-feedback amplifier is speedy

Wed, 14 Nov 2012 00:11:00 MST

The circuit in Figure 1 powers a microparticle and nanoparticle ion trap through a 1-to-5-turns-ratio, high-voltage transformer. It also works successfully as a driver for a piezo-tube scanner and in a near-field scanning optical microscope. The circuit is robust and works with supplies ranging from ±50 to ±230V.

Acceleration to Frequency Circuits

Tue, 13 Nov 2012 00:11:00 MST

High-side current sensor has period output

Sat, 10 Nov 2012 00:11:00 MST

You use high-side current monitoring in many battery-powered products that require accurate monitoring of load current, charger current, or both. In applications for nonportable designs, high-side-current monitoring serves as a power-supply watchdog that can flag a failure in downstream devices. The monitoring can also eliminate hazardous conditions by preventing power-supply overloads.

5V CAPACITANCE TOUCH ACTIVATED MOMENTARY SWITCH

Fri, 09 Nov 2012 00:11:00 MST

This circuit is discussed in more detail in the section on Capacitance Proximity Switch Technology. The circuit is powered from a standard +5v supply. It has both a source and sink output that change state whenever a metal button connected to the circuit is touched. An earth ground reference is required.

5 VOLT MOMENTARY OPERATION TOUCH SWITCH

Fri, 09 Nov 2012 00:11:00 MST

This simple circuit uses a single IC to form a nice touch switch circuit. A single transistor forms the remote active switch sensor. Multiple switches can be wired in parallel. The switch circuit can be located about 500 feet from the control circuit.

Dual-polarity peak detector operates from single supply

Fri, 09 Nov 2012 00:11:00 MST

The circuit inFig 1 can detect the peak of either positive or negative inputs, yet it operates from a single supply. The circuit uses two unity-gain amplifiers to monitor the input signal, one an inverting amplifier and the other a noninverting amplifier. A typical application is driving a VU meter. The design takes advantage of a characteristic of the LMC662, IC1. Although the op amps data sheet warns against pulling inputs below ground, the op amp can withstand negative inputs if you limit the input current. In this circuit, R1 limits input current to a very small amount.

Accelerometer Schematic

Sun, 04 Nov 2012 00:11:00 MST

Below is a rough schematic of the layout of the accelerometer PC board looking from the component side. The microcontroller is an Atmel AT89S8252, an 8051 clone. This microcontroller is in-circuit programmable using an SPI interface. The SPI pins are also used to drive the MMC. To permit the dual use there is a jumper block (located below the 74AHC244, marked "P" and "R") that allows the pins to be connected for programming (P) or running the code (R).

High-speed peak detector uses ECL comparator

Tue, 30 Oct 2012 00:10:00 MST

Professional electronics designers often use peak-detector circuit sin such applications as amplitude measurement, automatic gain control, and data regeneration. You can build a simple and fast peak detector from a serial diode and a shunt capacitor, but it suffers from serious inaccuracy that stems from the diode`s forward-voltage drop. On the other hand, precise detectors based on op amps are rather slow. They are therefore not well-suited for measuring pulses of a few nanoseconds` duration.

Acceleration sensing USB interface

Mon, 22 Oct 2012 00:10:00 MST

The TiltStick is a small acceleration sensing device in form of a USB stick. It's using a two axis acceleration sensor to measure acceleration (caused e.g. by motion and tilt). The device is emulating a USB joystick and can thus be used in conjunction with any USB equipped host (e.g. a standard PC or the Nokia N8XX family) without any special drivers. The TiltStick is the successor of the Tilt Dongle for Palm OS. Two versions of the TiltStick have been designed based on different 2D accelerometer chips. The slightly smaller one is based on the Analog Devices XL203 (the XL202 may also be used).

Peak detector maximizes CCD-sensor range

Wed, 17 Oct 2012 00:10:00 MST

To get the maximum performance from an optical instrument that uses a laser source and a CCD linear-array sensor (Figure 1a), an A/D converter should perform over the maximum possible range. You can maximize this range by stretching the upper reference of the flash A/D converter to coincide with the highest lit pixel in the CCD array. Most flash A/D converters allow you to control the extremities of the reference-resistor array. To compensate for optical-path variations, you can use the signal from the peak detector to control the light-source intensity.

Current-sense IC prevents overcurrent damage

Tue, 16 Oct 2012 00:10:00 MST

CMOS-interface ICs serve as gateways to the wired connections in electronic systems. Mishandling those external connections can damage the interface ICs by causing shorts to ground or by applying voltages that result in latch-up. The circuit in Figure 1 protects CMOS interface circuitry by sensing excessive currents. IC1 monitors the supply current (IS) to the interface circuitry and quickly removes current and voltage from the interface if IS exceeds a programmed threshold.

OPTICAL INTERRUPTER DRAWS MICROAMPS

Mon, 15 Oct 2012 00:10:00 MST

This circuit is great for battery-powered systems that use slotted type optical interrupters. It draws only 10uA from a 3v battery that should allow up to 5 years of operation from a lithium battery.

Sampling peak detector has shutdown feature

Thu, 11 Oct 2012 00:10:00 MST

You face a serious problem in using a slow ADC with a fast peak detector. The circuit in Figure 1 allows a slow ADC to measure a fast, sampled signal peak. The 100-MHz peak detector for ultrasonic-pulse sampling uses a fast MAX4231 amplifier from Maxim (www.maxim-ic.com). This amplifier has a shutdown feature that facilitates power savings without losing the sampled information. When the circuit samples a peak with a low-TTL-control input, the output of the peak-detector amplifier shuts off, and the output amplifier switches on to measure the output signal.

Cat / Dog Detector

Thu, 11 Oct 2012 00:10:00 MST

This can be used to control entry on a Cat or Dog Door" NOTE: There may be some changes and improvements coming. However this circuit does work and you can build it as shown. The PCB Shown below is Available from me, or make it yourself. It Measures 2.75" by 1.1". This circuit uses one tuned coil for on the door and just a single wire loop on the animals collar. When the two coils come close together, it produces a signal that can cause a an LED to light and also trips a solenoid to unlock the door so it can open. Since all these doors are somewhat different, I leave The Solenoid and Mechanical Parts of this design for you to figure out.

Reducing the Average Power Consumption of Accelerometers

Tue, 09 Oct 2012 00:10:00 MST

The use of a simple power cycling circuit provides a dramatic reduction in the average current consumption of the ADXL50 and ADXL05 devices.

remote-diode temperature-sensor

Mon, 08 Oct 2012 00:10:00 MST

Most remote-diode temperature-sensor data sheets recommend 10-mil PC board trace widths, and 10- mil spacing between traces for connecting the sensor to the thermal diode. However, narrower traces and closer spacing may be used, as illustrated in this application note. Though Maxim data sheets generally recommend 10-mil trace width and 10-mil spacing between traces, 5-mil traces and 5-mil spacing have been demonstrated to give equivalent results, but with higher series resistance. Because the measurement errors induced by the higher series resistance are predictable with Maxim temperature sensors and can be compensated, 5-mil traces and spacing may be used with good results.

Detection for trains on model railway

Mon, 01 Oct 2012 00:10:00 MST

This light valve can be used for example to detect trains on model railway or a lap counter at the close racing. D3 receives a constant stream of power built around T1. When the light beam from D3 to T3 is not interrupted, led T3 and T2 is the basis of practically grounded. T2 not conduct and the LED is not lit. When the beam is interrupted, spert T3 and T2 conducts and the LED will light. Of course listen to other things like LED control between plus and the collector of T2. Please note the maximum load of 100 mA. The supply voltage may be between 4.5 and 12 volts.

Peak detector lowers frequency-dependent errors

Fri, 28 Sep 2012 00:09:00 MST

The classic peak detector in Figure 1a lacks the necessary performance to drive an audio-level indicator. Because of the amplifiers slew-rate limitations, this circuit suffers a reduction in detected output with increasing frequency. The amplifier acts as a comparator. The output is low most of the time but slews up to "catch" the peak of the input signal when the voltage at the positive input exceeds that at the negative input. The amplifier output is, thus, a slew-rate-limited voltage spike. As frequency increases, this catch point occurs after the peak has passed; as a result, the held output demonstrates a frequency-dependent error.

Doorknob Proximity Alarm for wooden door

Mon, 24 Sep 2012 00:09:00 MST

Reverse engineered circuit diagram of a popular retail doorknob alarm. It contains a small transmitter and the doorknob acts as an antenna so it will not work on a metal door. When a person comes close to the doorknob this loads down the oscillator and the alarm sounds. The proximity sensor circuitry is perfectly capable of driving 74HCT series CMOS logic in place of of the sound effect IC`s shown in the circuit diagram.

Infrared beam barrier/ proximity sensor

Wed, 19 Sep 2012 00:09:00 MST

This circuit can be used as an Infrared beam barrier as well as a proximity detector. The circuit uses the very popular Sharp IR module (Vishay module can also be used). The pin nos. shown in the circuit are for the Sharp & VIshay modules. For other modules please refer to their respective datasheets. The receiver consists of a 555 timer IC working as an oscillator at about 38Khz (also works from 36kHz to 40kHz) which has to be adjusted using the 10K preset. The duty cycle of the IR beam is about 10%. This allows us to pass more current through the LEDS thus achieving a longer range.

Digital Capacitance Meter

Fri, 14 Sep 2012 00:09:00 MST

This is a simple capacitance meter which can measure capacitance value easy. There are some measurement methods for capacitance, at one time the capacitance was measured with a impedance bridge or a dip meter. Recently typical capacitance meters can measure capacitance and some additional characteristics from current vector by applying AC voltage to the Cx. Some simple capacitance meter use integration method that measureing transient response of the R-C network.

Tachometer demodulator has fast response time

Wed, 12 Sep 2012 00:09:00 MST

When a tachometer is a critical part of overspeed-shutdown circuitry, the response time of conventional demodulators may be too long. The circuit in the block diagram in Figure 1 provides updated speed data. The circuit provides corrections for variations in excitation amplitude and frequency at every excitation half-cycle. The circuit is independent of processors and, therefore, immune to software- and bus-related failures.

Infra-red detector circuit

Sat, 08 Sep 2012 00:09:00 MST

This circuit is a simple IR detector for testing IR remote controllers. The circuit is based on one phototransistor which receives the IR beam. The NPN transistor works as an amplifier which feeds current to the led. When this circuit detects IR or light, the LED is on. So you need to shield the phototransistor from ambient light if you don't want to do your tests in the dark. The best way is to fit the phototransistor in a small black tube. I used 2 cm long piece of insulating tube and fitted the phototransistor into the middle of the tube.

Integrator forms picoammeter

Wed, 05 Sep 2012 00:09:00 MST

The analog circuitry necessary to precisely resolve picoamperes can challenge even the best designer. At these minute current levels, noisy and nonreproducible circuit topologies are common. A current-to-voltage (I/V) converter that uses an op amp and large feedback resistor is the obvious first design choice to acquire a small current. However, the component errors that this method induces can swamp the measurable current (and can amount to throwing out the baby with the bath water).

Weather station

Wed, 05 Sep 2012 00:09:00 MST

This 1-Wire MicroLAN [1] uses a capacitor and diode half-wave rectifier to provide parasitic power from the data line for the station's various sensors and to transfer data (see Figure 1). Each sensor has a unique serial number that identifies it to the bus. The station is controlled by a PC or microprocessor executing Touch Memory Executive (TMEX) software. Data transfers are half-duplex and bit sequential over a single twisted pair using short and long time slots to encode the binary 1s and 0s.

Inexpensive peak detector requires few components

Wed, 29 Aug 2012 00:08:00 MST

Requiring no rectifier diodes, the positive peak-detector circuits in figures 1 and 2 exploit the open-drain output of a Texas Instruments TLC372 fast comparator, IC1. Both versions of the detector are simple and inexpensive and provide a buffered, low-impedance output at VOUT. In addition, the TLC372`s high typical input impedance of 1012 eliminates any need for an input buffer stage. As Figure 1 shows, the detector`s output voltage at the output of op amp IC2A applies a feedback signal for the comparator and acts as a reference level for comparison with the input signal`s amplitude. Upon first application of input signal VIN, the voltage on the hold capacitor, C1, is 0V, and VOUT is also 0V.

Pressure gauge responds linearly to altitude

Tue, 28 Aug 2012 00:08:00 MST

You can use a common pressure transducer as an altimeter if you employ a special technique to make the transducer respond linearly. If you were to simply amplify the output of a pressure gauge`s bridge (VB in Fig 1) by a gain of 32.7 and an offset of 3.2V, such a circuit would produce an output of 0V at sea level and 1V at 10,000 ft. However, this simple design would read 38.5 mV (385 ft), which is too high at 5000 ft. The nonlinear relationship between atmospheric pressure and altitude causes the error, which peaks at 3.85% of full scale.

Resistance calculator yields precise values

Mon, 27 Aug 2012 00:08:00 MST

For times when the nearest preferred resistor value isn`t close enough to the desired value, a program comes in handy. (You`ll find the executable ZIPfile and several source-code files for the program in EDN BBS /DI_SIG #1740.) The program finds all combinations of two series or parallel connected resistors, within a specified tolerance of the required value, using only preferred values from the E6, E12, E24, and E96 ranges (6, 12, 24, and 96 different values per decade).

Audio signal Indicator

Mon, 27 Aug 2012 00:08:00 MST

This circuit can be used to remotely monitor a loudspeaker, alarm, or audio source for presence of an audio waveform. It can also be directly connected across loudspeaker terminals used as a peak indicator. If you need to monitor some audio signal at a location that is either soundproof are too far away to actually hear the signal then you can use a circuit similar to this one. A remote indication that the audio source is active is provided visually, here in the form of a LED. Referring to the above circuit, the 10k preset is a level control which should be adjusted so that when the source ( audio signal or alarm ) is producing the desired amount of noise, the LED lights.

RS-232C link monitors animal activity

Sun, 26 Aug 2012 00:08:00 MST

The circuit in Figure 1 allows you to effect long-term, unattended collection of animal-behavior data using any standard PC with an RS-232C port. The circuit detects changes in the proximity of the animal subjects to a capacitive sensor electrode. The multivibrator comprising IC1D, IC1E, and IC1F drives the electrode with a 5V p-p, 200-kHz square wave.

Current sensor measures 0 to 500A

Sat, 25 Aug 2012 00:08:00 MST

The simple circuit in Figure 1a can sense both low and high current levels without low sensitivities or loss of accuracy either at the low or the high end of the scale. The circuit is useful for discerning either low or high currents in noisy environments.

sound detector tone decoder

Thu, 23 Aug 2012 00:08:00 MST

This circuit is designed to trigger on a 1 khz tone. to change this frequency - refer to the table below, then change the resistor and capacitor values accordingly.

Machine vibration activates hour meter

Wed, 22 Aug 2012 00:08:00 MST

Battery-powered digital hour meters commonly monitor how long a machine is in operation by detecting when the machine is supplied with power. However, it is often difficult or dangerous to connect a battery-powered hour meter to a line-powered machine. When the machine being monitored produces de-tectable vibrations, you can use the circuit in Figure 1, which doesn`t require any power-line connections. The circuit uses just one IC and allows you to turn a battery-powered hour meter on and off according to a machine`s vibration.

How to Build an Inexpensive Seismometer

Mon, 20 Aug 2012 00:08:00 MST

These pages describe my project to build simpler and less expensive amateur seismometers by using microprocessors and other new chips, such as switched capacitor filters. I have tried to provide links to much of the excellent information that is already on the web. And I have tried to fill in some of the gaps in the existing information.

Current-sense amplifier precisely measures low side

Wed, 15 Aug 2012 00:08:00 MST

Several integrated high-side current-sense amplifiers, such as the MAX4172 (Maxim Integrated Products, www.maxim-ic.com), make it easy to measure the current from a positive power supply. With a couple of resistors, these devices provide a ground-referenced voltage output that is proportional to the delivered current (Figure 1a).

Peak Reading Audio Level Meter

Tue, 14 Aug 2012 00:08:00 MST

Using minimum component count; this simple circuit will indicate peak audio response on an analogue meter, similar to a tape recorders meter. The circuit uses an opamp as a non inverting amplifier, but with one addition - a diode in the feedback loop. The circuit has a fast response time and slow decay time to indicate peak readings. The 1N4148 diode provides half wave rectification of the input signal, the dc output being smoothed by the 22u capacitor.

Tactile sensors Motor controller

Sat, 11 Aug 2012 00:08:00 MST

It's basically a photovore with a couple tactile sensors. It's rather complex but can give neat behaviors with modifications to the circuit. At this point I don't have any plans to give more information on this circuit so your on your own. C1 and C2 values C1 and C2 are the capacitors that control how long each motor will reverse after the tactile sensor is triggered. Increasing the value will cause your bot to turn more after bumping an object. Decrease and it will turn less. The layout All resistors are 1M unless labeled otherwise. All capacitors are .22uF unless labeled otherwise. This circuit is more for advanced BEAMers so if your a newbie to BEAM I would recommend the iVore circuit. I may get some more info on the circuit on the web but no plans yet.

Electronic Distance Meter

Thu, 09 Aug 2012 00:08:00 MST

This project demonstrates the use of 16x1 line LCD module to interface with Nitron 16-pin MCU, 68HC908QY4. The original idea came from one evening I went out with my son to the park near my home in Korat. The park has a nice walking way for people to exercise.

sound detector switch

Thu, 09 Aug 2012 00:08:00 MST

When the 555 ic goes into timing mode (triggered by an output signal from the sound detector amplifier,) the timer`s output (pin 3) is set into HIGH for a duration set by C2, and R2. adjusting R1 will adjust how long it listens, from 10 seconds all the way down to 2/10ths of a second. this could be used to listen for hand claps.

Ultrasound Detector with 567PLL and LM386 ICs

Mon, 06 Aug 2012 00:08:00 MST

The bat ultrasounds are picked up by the microphone SPKR1 and go through two stages of amplification at Q1 and Q2. Separately, a tunable (R12) single frequency is produced by the LM567 oscillator U1. The LM567 is a tone decoder but here its input is grounded and its voltage controlled oscillator is used as a precision oscillator.

AccelR8

Sat, 04 Aug 2012 00:08:00 MST

The schematic show that the AccelR8 only uses 3 IC`s. An AVR 8515 microcontroller do the calculation work and controls the other circuits. An MAX603 controls voltage and power-on/power-off. And the chip that makes it all possible, the ADXL202 from Analog Devices measures the acceleration.

High-side current monitor operates at high voltage

Wed, 01 Aug 2012 00:08:00 MST

The simplest technique for measuring current in an actuator or a motor is to monitor the ground current with a resistive element between the load and the ground. Because the device and its associated electronics share a ground potential, you need to amplify only the ground-current signal. This approach, however, does not detect device short circuits to ground, which can overload the high-side drive circuitry.

EMF radiation Sleeping Aid

Mon, 30 Jul 2012 00:07:00 MST

Many people experienced sleeping well in natural surroundings, into a tent or a wooden hut. This fact is due not only to the healthy atmosphere but also from our unconscious ability to perceive natural Earth`s magnetic-fields. The circuit generates this type of Geo-magnetic-fields and lets us perceive them: in this manner our brain is surrounded by an ideal environment for a sound sleep. Generates a natural electromagnetic-field. Makes easier to fall asleep. Induces a prolonged and sound sleep without drugs. No side effects.

Audio Signal Detector Switch

Tue, 24 Jul 2012 00:07:00 MST

This circuit will activate a transistor switch when it detects at least 50mv peak to peak of an audio signal. It could be used to turn on a relay, routing the signal to were it is needed.

MOSFET current sensing

Sun, 15 Jul 2012 00:07:00 MST

The circuit shows the method of `mirror` current sensing a MOSFET. A fully conducting MOSFET is resistive and behaves exactly as a resistor. It therefore you limit the voltage across the MOSFET when it is conducting you automatically limit the current flowing through it. In addition the MOSFET``s on resistance has a positive temperature coefficient so as it warms up, keeping the voltage across it limited will automatically reduce the limited current flowing through it, keeping it within its safe region over a wide range of junction temperatures.

RS-232C link monitors animal activity

Tue, 10 Jul 2012 00:07:00 MST

A common need in biological experimentation is the ability to unobtrusively monitor the activity of small caged animals, such as mice, rats, and rabbits, as they move about their enclosures. This monitoring must be over long periods and around the clock. The circuit in Figure 1 allows you to effect long-term, unattended collection of animal-behavior data using any standard PC with an RS-232C port.

A 4- to 20-mA loop needs no external power source

Mon, 09 Jul 2012 00:07:00 MST

The simple circuit in Figure 1 uses a low-current-drain MAX4073H amplifier to sense the current flowing through a 4- to 20-mA loop. The circuit senses the current through a 1 resistor with a fixed gain of 100 and uses no battery or dc power supply. The low current drain of the amplifier (0.5 mA) enables the circuit to tap its power from the 4- to 20-mA loop to power the amplifier chip. Note that the current flowing in the amplifier`s power-supply Pin 3 (nominally 0.5 mA but may vary slightly) is not part of the sensing loop.

Video Activated Relay

Sun, 08 Jul 2012 00:07:00 MST

This simple circuit from the May 1996 Think Tank column of Popular Electronics activates a relay when it senses a composite video signal. This allows you to use the tuner built into your VCR to turn on and off older TVs that are not equipped with a remote. It can also be used to activate surround sound equipment, turn off the room lights, turn on video game consoles, etc. For such a simple circuit, it is very versatile.

Toy Train rail detector circuit

Sun, 24 Jun 2012 00:06:00 MST

This circuit must be used between the drive voltage of such a transformer and track. On JP1, the transformer is connected to JP2, the rails are connected to JP3, is a TTL "High" position when there is a tax on the trail is more of 2mA, but given the average LED more consumption, this should not be a problem. Works through a circuit voltage of 1.4 volts over the diodes, which are anti-parallel so that the circuit in both directions to use.

Increasing the Frequency Response of the ADXL Series Accelerometers

Fri, 22 Jun 2012 00:06:00 MST

The ADXL series of accelerometers are specified and tested for operation over the range from dc to 1 kHz typically. However, in many applications, such as vibration monitoring, a wider bandwidth is required. The bandwidth of these accelerometers can be increased by decreasing the demodulator capacitance.

Audio acquires the "write" touch

Tue, 19 Jun 2012 00:06:00 MST

This power-stingy combination of an audio codec and touchscreen-interface controller now comprises a differential or two-channel microphone input with automatic level control, a two-channel audio-line input, a separate monophonic-audio input, a PC-"beep" input, and an audio DAC that connects to the AC`97 Version 2.2 system interface.

Toy Train rail detector circuit II

Mon, 18 Jun 2012 00:06:00 MST

This circuit can detect whether a train in a particular drive. The output is TTL and CMOS compatible and can be processed by such a computer. The simple circuit works. The driving voltage is connected to the two terminals left. When the locomotive of the interrupted line is, the flow leading to the locomotive goes through the triac T1. This is then a voltage of about 1 V, which is conducting T3 or T4. Therefore, the LED D1 on and the output is logical zero.

Audio Detector switch

Sun, 17 Jun 2012 00:06:00 MST

The following circuit can be used to detect those annoying piezo whistles that one can get from Radio Shack. For the Trinity Home Fire Fighting Contest, additional points accrue when the robot is started by a sound similar to a fire alarm. The actual whistle is specified as a particular Radio Shack piezo element, but the following circuit should be tunable across a wide range of pitches.

Low Value Capacitance Meter

Sat, 16 Jun 2012 00:06:00 MST

This circuit was originally designed to measure the volume of fluid inside a medical syringe. As designed, it produces a zero to 5 volt output, corresponding to a capacitance change of about 10 picofarads. With a digital voltmeter, at its output, it can resolve a capacitance change of 0.002 picofarads or 2 femtofarads.

Using Accelerometers in Low g Applications

Thu, 14 Jun 2012 00:06:00 MST

Accelerometers can be used in a wide variety of low g applications such as tilt and orientation, vibration analysis, motion detection, etc. This application note explains how to best apply the ADXL50 (50 g) and ADXL05 (5 g) accelerometers when measuring signals at the low end of their respective full-scale ranges.

ISOLATED AC CURRENT MONITOR

Mon, 11 Jun 2012 00:06:00 MST

This circuit uses a small AC current transformer from Magnetek to produce an isolated voltage proportional to the AC current in the primary winding. The transformer contains a single turn primary with a low 0.001-ohm resistance. It can easily handle 30 amps of AC current and provides at least 500vac of isolation. With the components shown, the output AC voltage is scaled so 1 amp of current produces 100mv of AC voltage.

Human Traffic Footstep Detector

Fri, 08 Jun 2012 00:06:00 MST

This circuit uses a surplus geophone to detect human footsteps from 100 feet away. It was designed for monitoring the Mexico/USA border. This preamp part of the system draws about 50 microamps from a 12 volt supply.

Infra-red Level Detector with 555

Mon, 04 Jun 2012 00:06:00 MST

Useful for liquids level detection and proximity devices Up to 50 cm. range, optional relay operation. This circuit is useful in liquids level or proximity detection. It operates detecting the distance from the target by reflection of an infra-red beam. It can safely detect the level of a liquid in a tank without any contact with the liquid itself. The device`s range can be set from a couple of cm. to about 50 cm. by means of a trimmer. Range can vary, depending on infra-red transmitting and receiving LEDs used and is mostly affected by the color of the reflecting surface. Black surfaces lower greatly the device`s sensitivity.

Transistor Pin Identifier

Mon, 04 Jun 2012 00:06:00 MST

Tests transistors and diodes for polarity. A three-phase wave form is derived from the 350Hz ring-of-three oscillator formed by IC1A, IC1B and IC1C, and applied to the device under test via the LEDs. The oscillator wave form enables each pair of device terminals to be forward, reverse and unbiased for one third of a cycle. Simple circuitry - 9V Battery operation.

Method offers fail-safe variable-reluctance sensors

Fri, 01 Jun 2012 00:06:00 MST

Variable-reluctance sensors are preferred for industrial and automotive environments, because they sustain mechanical vibration and operation to 300°C. In most applications, they sense a steel target that is part of a rotating assembly. Because the unprocessed signal amplitude is proportional to target speed, a sensor whose signal-processing circuitry is designed for high speed ceases to function at some lower rate of rotation. Hall-effect sensors are preferable for speeds of several pulses per second, but they require the attachment of a magnet to the rotating assembly.

Current Loop Sensor Interface

Fri, 01 Jun 2012 00:06:00 MST

This is a very simple circuit to interface a current loop sensor to an input which is designed for a voltage, such as that from a standard potentiometer. This page is technical so that interested persons can build the circuit themselves, but 4QD can also supply the interface on a 'postage stamp' sized (22mm x 27mm) board as shown in the first diagram. It is a relatively trivial circuit! This circuit was developed to interface one of the new type contactless (inductive) throttle sensors to 4QD's motor controllers for use in a conversion to an Eze-Go golf car.

Analog-input circuit serves any microcontroller

Thu, 31 May 2012 00:05:00 MST

The simple ADC in Figure 1 is perfect for getting analog signals into a purely digital microcontroller. Using just five surface-mount parts, you can assemble it for less than 50 cents (1000), which is approximately half the cost of a single-chip-ADC approach in the same volume. Moreover, this design takes only one pin from the microcontroller to operate. Although you can purchase many microcontrollers with built-in ADCs, in some circumstances, this solution is impractical. For example, you might have an all-digital microcontroller already designed in.

Battery Current Sensor

Tue, 29 May 2012 00:05:00 MST

These controllers have an inhibit input and the effect of shorting this down to ground is to turn down the internal demand speed. So with the battery current limiter fitted, the internal demand speed can only ramp up to a value which engages the limit. Some enthusiasts of electrically assisted cycles believe constant power acceleration is the ideal response. Although personally I am not convinced that constant power acceleration is the ideal, limiting the battery current gives constant power acceleration whenever the limit is engaged.

AC Current Monitor

Fri, 25 May 2012 00:05:00 MST

This circuit was designed on request, to remotely monitor when a couple of electric heaters have been left on. Its sensor must be placed in contact with the feeder to be able to monitor when the power cable is drawing current, thus causing the circuit to switch-on a LED.

CAPACITANCE TYPE LIQUID LEVEL MONITOR

Thu, 24 May 2012 00:05:00 MST

This circuit was originally designed to monitor the level of liquid natural gas in a tank but it can be used to also measure almost any liquid. Two custom insulated metal tubes form a capacitor plate. The capacitance between the two tubes increases as the level of the liquid rises. The circuit converts an increase of capacitance into a positive voltage change. The circuit could be changed to handle almost any scale factor needed.

Optocoupler extends high-side current sensor to 1 kV

Wed, 23 May 2012 00:05:00 MST

The task of sensing dc current at high voltage is often problematic. Most high-side current-sensing ICs available off the shelf are good only to 30 or 40V. Combining an optocoupler with such an IC yields a sensing circuit in which the only limitation of the high-side voltage is the optocoupler`s standoff voltage (Figure 1).

IR distance ranger covers 1 to 20 cm

Wed, 23 May 2012 00:05:00 MST

Touch Switches Collection

Sun, 20 May 2012 00:05:00 MST

Touch operated switches are an attractive project for DIY electronics but they are not so common in commercial products. The reason for this is that, although there are many different ways of implementing a touch switch (leakage, hum pickup, capacitance, albedo) all of them rely on body parameters which vary a lot with the person's body, age and environment so that a circuit which gives reliable operation with one development engineer may cause problems in use with, for instance, old folks living in arid areas. Nevertheless touch switches can give excellent results.

Optical tachometer provides bidirectional info

Sat, 19 May 2012 00:05:00 MST

Optical tachometers have many advantages in precision servo applications. Compared with dc-generator types, optical tachs are relatively inexpensive and, because they lack wear-prone commutator brushes, they`re long-lived. Frequency-to-voltage conversion circuits provide a convenient means to integrate the output of optical tachs into analog, unidirectional motion-control loops. However, for bidirectional servos, where you need a bipolar angular-velocity readout, you need a more unconventional solution, such as the circuit in Figure 1.

Limit Temperature Buzzer

Sat, 19 May 2012 00:05:00 MST

The circuit is small regulatorof temperature, us warns for the increase of temperature. The control of temperature becomes from the thermistor TH1, that is negative factor. His resistance is altered between in the 10K in temperature 25° C and roughly in the 1K in their 94° C. The trimmer TR1 regulates the precise temperature in which the Q1-2, connected as darlington, conduct, making him relay K1 close also the buzzer BZ, sound. The alarm is activated when the temperature becomes bigger than predetermining. The thermistor it should he is placed far from the remainder circuit, in order that this is not in danger from the temperature.

Embedded Shock and Temperature Recorder

Wed, 16 May 2012 00:05:00 MST

Whenever a package is shipped, whether it contains an expensive piece of equipment or perishable food items, shocks and extreme temperatures can adversely affect its contents. Many types of equipment, no matter how ruggedly designed or carefully packaged, can be susceptible to mishandling.

Leak Detector

Sat, 12 May 2012 00:05:00 MST

High sensitivity, portable temperature comparator. This sensitive circuit is basically a comparator, detecting very slight temperature changes in respect to the ambient temperature. It was primarily intended to detect draughts around doors and windows that cause energy leaks but can be used in many other ways, when a sensitive temperature change detector is needed. Two LEDs are used to signal if the temperature change is pointing above (Red LED) or below (Green LED) the ambient temperature. Detects draughts around doors, windows, etc.

Magnetic proximity sensors

Wed, 09 May 2012 00:05:00 MST

Tone detector / Sound Activated switch

Wed, 09 May 2012 00:05:00 MST

The detector (below) is a bit more complex. It amplifies a microphone and sends the resulting signal to an NE567 tone decoder. The amplifier is half of a 1458 opamp. The two 120K resistors attached to pin 3 keep the opamp's average output at about halfway between the 5 vdc source and ground. These resistor values are non-critical, but should be equal. The 120K feedback resistor from pin 1 to 2 establishes the gain of the amplifier and the sensitivity of the detector to a generated tone. I found that 120K gave me pretty reliable operation at about with the generator about 3 feet from the microphone. You can vary this resistor to make the detector more or less sensitive if you wish. More resistance makes it more sensitive.

Circuit senses high-side current

Tue, 08 May 2012 00:05:00 MST

infrared beam proximity detector

Fri, 04 May 2012 00:05:00 MST

his circuit can be used as an Infrared beam barrier as well as a proximity detector. The circuit uses the very popular Sharp IR module (Vishay module can also be used). The pin nos. shown in the circuit are for the Sharp & VIshay modules. For other modules please refer to their respective datasheets. The receiver consists of a 555 timer IC working as an oscillator at about 38Khz (also works from 36kHz to 40kHz) which has to be adjusted using the 10K preset. The duty cycle of the IR beam is about 10%. This allows us to pass more current through the LEDS thus achieving a longer range.

Rain Detector

Fri, 27 Apr 2012 00:04:00 MST

This circuit uses a sensor made of a small piece of etched PC board and a simple SCR circuit to detect rain and sound a buzzer. The SCR could also be used to activate a relay, turn on a lamp, or send a signal to a security system.

Digital Engine/Race Computer Board

Thu, 26 Apr 2012 00:04:00 MST

After (years) of mucking about with this, I finally put together a really slick tach that I`ve had in use for a long time. PCBs are available to experiment with, the source code and schematics are open, the code is well tested and mature, so what are you waiting for?

Circuit breaker monitors leakage current

Tue, 24 Apr 2012 00:04:00 MST

The residual-current circuit breaker in Figure 1 continuously monitors the supply lines for any leakage current and immediately disconnects the supply if necessary. Load-supply wires, both live and neutral, pass through the magnetic core of the CR4311-5 transducer (http://www.crmagnetics.com), which monitors the supply current. Under normal circumstances, because the current flowing in both conductors is equal and opposite, no flux is generated in the transducer core.

Mains-operated Capacitive Sensor

Sun, 22 Apr 2012 00:04:00 MST

This very simple circuit acts as a high sensitivity capacitive sensor. Lamps and/or Buzzers are operated at half the mains supply voltage when a part of the human body comes in contact with the sensor or approaches it at a close distance. The circuit can be used as an alternative to the Door Alarm or Capacitive Sensor circuits, already available on this website.

Heating System Thermostat

Sat, 21 Apr 2012 00:04:00 MST

This circuit is intended to control a heating system or central heating plan, keeping constant indoor temperature in spite of wide range changes in the outdoor one. Two sensors are needed: one placed outdoors, in order to sense the external temperature; the other placed on the water-pipe returning from heating system circuit, short before its input to the boiler. The Relay contact wiring must be connected to the boiler`s start-stop control input.Controlled by indoor and outdoor temperature Simple, high reliability design.

Room Noise Detector

Fri, 20 Apr 2012 00:04:00 MST

One LED monitors three levels: 50, 70 & 85 dB Useful to detect too noisy environments. This circuit is intended to signal, through a flashing LED, the exceeding of a fixed threshold in room noise, chosen from three fixed levels, namely 50, 70 & 85 dB. Two Op-amps provide the necessary circuit gain for sounds picked-up by a miniature electret microphone to drive a LED. With SW1 in the first position the circuit is off. Second, third and fourth positions power the circuit and set the input sensitivity threshold to 85, 70 & 50 dB respectively.

Peak-Reading Meters

Sun, 15 Apr 2012 00:04:00 MST

Peak reading meters, popular in Europe for years, are just now coming into greater favor in America, and for good reason. The main purpose for having a VU meter is obviously to monitor signal levels going to a tape recorder, reverb unit, or some other level-sensitive device, to help optimize the signal to noise ratio of the audio sent to the device. Too much level will produce distortion, and too little results in the inherent noise of the medium becoming a problem. Unfortunately, a conventional VU meter responds to the average level of the program material and not to the peaks; yet it is these momentary bursts of higher level that become distorted first.

PRECISION AC PEAK DETECTOR

Wed, 11 Apr 2012 00:04:00 MST

This unique circuit uses a very inexpensive voltage comparator to form a peak detector. The DC voltage produced tracks the positive peak of the input signal. It works from about ten millivolts to about 10 volts peak to peak. The maximum frequency is about 150KHz.

Precision peak detector uses no precision components

Sat, 07 Apr 2012 00:04:00 MST

When you need a precision peak detector, you would usually implement it with one or several op amps and a few other associated components. This technique usually works well unless your design requires operation higher than a few kilohertz. In designs requiring such operation, the accuracy of the circuit severely deteriorates unless at least one of the amplifiers has a high slew rate and frequency response extending to tens or even hundreds of megahertz. Performance depends on the desired frequency response and peak-to-peak input-voltage range of the peak detector (Reference 1).

Two diodes change demagnetization-signal polarity

Wed, 04 Apr 2012 00:04:00 MST

Power-supply designers usually like flyback converters to operate in DCM (discontinuous-conduction mode) rather than in CCM (continuous-conduction mode). In DCM, the flyback converter is a first-order system at low frequencies, which eases the feedback-loop compensation. You can use a low-cost secondary rectifier, thanks to soft blocking conditions. In DCM, IP goes to zero, and the diode stops conducting, whereas the power-switch turn-on event in CCM forces the diode to brutally stop conducting.

shock and vibration detector

Sun, 01 Apr 2012 00:04:00 MST

This circuit outputs a positive pulse upon sensing vibration. It can drive high impedance CMOS logic input having a threshold of approximately VDD/2