Various Circuits

Crystal display (LCD) tester

Crystal display (LCD) tester

Liquid crystal displays are currently available in several versions and various sizes. The wide variety of features, has resulted in there a little chaos in the provision of the pin. So that even when, after much effort, we can find a screen that fits our needs, we are rather difficult to use it. And because most likely we can not find technical manuals to describe all that remains is for us to try to locate the pins by making successive trials. For this work the circuit described below is particularly useful and convenient. An LCD consists of two thin sheets of glass are few among them. ..

Static charge-electricity detector

Static charge-electricity detector

The detector will sense static charges and free ions in the air. It can be used to indicate the presence of ion emission, high voltage, static electricity, and electrostatic fields. The ground can be an earth ground or a touching metal by your hand. the meter is 100uA range. and R3 potentiometer is by controlling the sensitivity of the detector...

Car Exhaust Meter

Car Exhaust Meter

Bridge circuit contains two resistors lOO-ohm (R3 and R4), and two thermistors (Tl and T2). At room temperature, the resistance of T1 and 1'2 is about 2000 ohms. When they are each heated to 150 ° C by an RNA 10 current, the resistance value decreases to 100 ohms. So. the four elements include a bridge circuit. CO is a characteristic that conducts heat from a thermistor at a rate different from that of air. A thermistor, TI, is exposed to automobile exhaust, while the other, 1'2, is isolated in an environment of clean air. Unlike thermal conduction bridge imbalance. A voltage difference is caused between points A and C. A differential amplifier. VI, amplifies this difference and leads to the counter with a current sufficient to read the percentage of CO and air-fuel ratio. A control panel before the balance, R5, balances the bridge and calibrates the instrument. The calibration is performed when both thermistors are exposed to outside air. ..

Km Counter / meter circuit

Km Counter / meter circuit

This circuit measures the distance covered during a walk. Hardware is located in a small box slipped in pants' pocket and the display is conceived in the following manner: the leftmost display D2 (the most significant digit) shows 0 to 9 Km. and its dot is always on to separate Km. from hm. The rightmost display D1 (the least significant digit) shows hundreds meters and its dot lights after every 50 meters of walking. A beeper (excludable), signals each count unit, which occurs every two steps. A normal step is calculated to span approx. 78 centimeters, thus the LED signaling 50 meters lights after 64 steps or 32 mercury switch's operations, the display indicates 100 meters after 128 steps and so on. For low battery consumption the display lights only on request, pushing P2...

Analogue Tachometer and Dwellmeter

Analogue Tachometer and Dwellmeter

This circuit as first published in Wireless World September 1975 and subsequently in MECRM. It's built around a TTL quad NOR gate, though CMOS could be used...

220V Mains Quality Monitor

220V Mains Quality Monitor

With this circuit you will be able to monitor the quality of the mains. There are 4 distinct sections, each supervising a parameter pertinent to the quality of the supply line. The noise section consists of a 50Hz filter and a speaker where you will hear the noise present on the line. The bicolor LED should be adjusted for the least light with the 5k pot and gives a visual indication of noise or asymmetry in the wave. The second section will detect any spike which is overimposed on the mains voltage: adjust the pot so that it will not trip if you just switch on the light, sensitivity is high enough to detect a switching operation from a close neighbor. ..

Lead Acid Battery Charger with voltmeter

Lead Acid Battery Charger with voltmeter

This simple circuit makes it posible to monitor the charging process to a higher level. If you need more information then check out the LM3914 Datasheet. Final adjustsments are simple and the only thing needed is a digital voltmeter for the necessary accuracy. Connect an input voltage of 12.65 volt between the positive and negative poles and adjust the 10K trimmer potentiometer until Led 10 lights up. Lower the voltage and in sequence all other Led's will light up. Check that Led 1 lights up at approximately 11.89 volts. ..

How to calculate toroidcoils

How to calculate toroidcoils

This side will explain how to calculate toroidcoils. I have made toroid tests with different number of turns and measured the inductance. Formula : L (nH) = N2 *AL. Where: L = inductance in nanohenrys. n = number of turns. AL = inductance factor. ..

RF probes

RF probes

An RF probe is used to directly measure the level of RF voltage present at a particular point and is one of the most useful test instrument in the hands of the home brewer. It is normally used with a digital multi meter to indicate the voltage level as dc voltage which is equivalent to the RMS value of the RF voltage being measured. However, the level of RF voltage being measured provides useful information only when the probe has been designed for use with a specific multi meter. The design of the RF probe is a function of the DC input resistance of the meter we intend to use with it. If a new meter with a different input resistance is used with the probe the reading will be inaccurate...

Negative Resistance Oscillator with Tunnel Diode

Negative Resistance Oscillator with Tunnel Diode

This circuit can be easily powered from a 1.5 volt battery. One characteristic of N type negative resistance devices is that they typically require a very low bias source resistance in order to keep the bias voltage stable within the negative resistance region. With too high of bias resistance, the voltage, as it enters the negative resistance region, will have a tendacy to suddenly jump past it. This is why a gap is seen in the curve (see photo). This homemade device, with its narrow negative resistance region, requires an even lower bias source resistance than a typical tunnel diode. A typical tunnel diode can be biased within the negative resistance region with a bias resistance of around 20 ohms. This device works best when the bias resistance is 1 ohm or less. ..

16-300 MHz Testing Colpitts oscillator

16-300 MHz Testing Colpitts oscillator

The circuit is a modified Colpitts oscillator, tuned with MV209 varactor diodes. The resonating inductor and the drain choke are selected by a rotary switch. 1N5711 Schottky diode, D, clamps the maximum positive voltage on the gate of oscillator FET, Q1 to just above ground to reduce the distortion in the wave form on the gate of Q1. Buffer Q2 provides about 1.8 volts peak-to-peak at 20 MHz to drive a frequency meter. Since the P-P voltage on the gate of Q1 is too large to be buffered by a 2N5485 without sever distortion -see the pictures further down this page), the signal is reduced by a capactitive voltage divider formed by 1 picofarad capacitor C11 and the input capacitance of Q3. This results in about 650 millivolts on the gate of Q3, and about the same on the source. ..

Scope Probe Adapter

Scope Probe Adapter

The capacitance between the wire and the probe would form a capacitive voltage divider with the probe's input capacitance, and at frequencies significantly higher than the low frequency roll off created by the probe's input capacitance and the probe's resistance, the wave form would be faithfully reproduced, although it would have a reduced amplitude. The circuit give here, presents about a 2 pf load to the circuit, and capacitively loads the circuit measurably less than the X100 voltage probe (A Stack CP-241) I often use for this sort of thing. ..

1 Khz Inductance Meter ATTINY861

1 Khz Inductance Meter ATTINY861

1 kHz is a commonly used test frequency, and I resolved to see if I could make an inductance meter that uses a 1 kHz test signal at a low level. I also wanted to use a low level test signal so that the test current would have a minimal effect on the measurement. Magnetic cores, and soft ferrites in particular, change in permeability as a function of the current through the winding. I chose 1.0 milliamps peak-to-peak as a test current. Given that I wanted to be able to measure inductance down to 100 uH, my attention turned to the problem of how to accurately measure the amplitude and the phase of as little as 63 millivolts across a 100 uH inductor. ..

µCurrent Adaptor for multimeters

µCurrent Adaptor for multimeters

The µCurrent is in many cases also able to improve upon your meters current range accuracy by using your meters more accurate mVDC or mVAC voltage ranges instead to display the DC or AC current. With AC the frequency response extends flat up to 10KHz, but THD increases substantially above 2KHz. Still a very respectable AC response range, surpassing that of many meters on current and voltage ranges. Typical accuracy of the µCurrent itself is better than 0.2% on the µA and nA ranges, and 0.5% or better on the mA range. Unfortunately it is not easy to obtain a 0.1% precision shunt resistor for the mA range, as the 10 milliohm value is too low...

RF Field Strength Probe

RF Field Strength Probe

This broadband probe has a small antenna (about a 15 cm length of insulated wire). Radio Frequency energy coupled to the antenna is detected and made available to drive millivolt level signals to the input of a DVM (Digital Volt Meter). Its battery powered for convenience with very low current drain and automatic shutdown for long battery life. I've used the circuit shown below to check the output of transmitters at 4 MHz, 35 MHz, 55 MHz, 100 MHz, 900 MHz, a cell phone, and a microwave oven. It really is broad band, though I don't make any claims for the flatness of response. Since the collectors and emitters of the detector transistor are both at RF ground, choice of transistors isn't all that critical. ..

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