Vacuum Tubes Valves
Musical & effects
Yagi Uda Antennas
Metal Detector Circuits
Liquid Sensing Circuits
Light Sensing Circuits
Voltage Detector Circuits
Air-Gas Detection Circuits
Human Sensing Circuits
RF & Radiation
Optical Sensing Circuits
Free Energy Circuits
AC to DC & DC to DC
Solar Cell Circuits
Micro Power Circuits
Switching Power Supplies
Light Laser LED
Digital to Analog
Analog to Digital
Data Bus Circuits
Voltage to Pulse
Current to Voltage
Frequency to Voltage
RF Converter Circuits
Sine to Square Wave
Voltage to Current
voltage to frequency
Period to Voltage
Video Wall circuits
TV Video Circuits
Motor Control Circuits
8051 / 8052
PCB CAD Software
Car bike Circuits
555 Timer Circuits
Remote Control Toy
H Bridge Circuit
Interconnection & Timing
Digital Signal Integrity
Digital & Bipolars
Sensors & Detectors
Regulated Power Supply
4 Band Resistor
5 Band resistor
6 Band resistor
Meter Counter Circuits
Working on live telephone circuits can be a problem. You just can't connect a normal scope probe to the circuit while it is tied to the phone line. Neather side of a phone line is ground. When a phone or other device is 'offhook', one side floats at about -22 volts and the other side about -30 volts. This probe allows connecting to such...
Dual-trace, triggered oscilloscope
This site contains public-domain schematics for a dual-trace, triggered oscilloscope, and some theory. Click on the topic in the table below to see the schematic for that block. I designed and built this oscilloscope in 1986 using the chassis of a non-working vacuum tube oscilloscope, keeping only the original high voltage vacuum tube supply and...
Horizontal Deflection Amplifier for Oscilloscope
The circuit below provides the horizontal drive voltage. The supply voltage on one end, +135 to +165, is made variable for the horizontal position control.
Blanking Circuit for Oscilloscope
This circuit blanks the CRT starting just before retrace begins. Since the CRT sits at a -1200 volt potential, the blanking circuit must also be based at -1200 volts. Note the capacitors, C40, C41, and C43 which allow the gates that drive the intensity grid of the CRT to be isolated from the other electronics within the oscilloscope.
CRT and Power Supply for Oscilloscope
The high voltage section of the CRT is unchanged from the original vacuum tube oscilloscope used as the basis of this design. The CRT requires shielding from the main power transformer. Cold roll steel around the CRT does not provide enough shielding from the 60Hz magnetic field. There are certain nickel alloys, such as mu-metal, that provide...
Vertical Deflection Amplifier for Oscilloscope
The vertical deflection amplifier uses a 180 degree phase splitter to generate a differential signal. The CRT requires large drive voltages, but almost no current. The oscilloscope bandwidth is limited by the amplifier chain as almost all electrostatic CRTs have a bandwidth extending to several hundred megahertz.
Analog Switch for Oscilloscope
The analog switch multiplexes between channel 1 and channel 2 at the end of each sweep. Controls include Dual Trace/Single Trace mode, sync polarity, sync level, and sync on + or - (rise or falling) edges.
DC-10Mhz Amplifier for Oscilloscope
The DC-10 MHz amplifier shown below is identical for both scope channels. The input FET should be mounted directly on the adjustable attenuator switch for best frequency response. The vertical position pots, R27 and R51, change the dc level of the traces, but do not affect the ac signal. There is no fine (variable) gain adjustment in this...
Adjustable Attenuator for Oscilloscope
The input attenuator uses a commutating capacitor to cancel the input capacitance of the FET buffer (see DC-10 MHz amp schematic). The commutating capacitors are absolutely necessary to cancel the effect of the input capacitance to the DC-10MHz amplifier. The theory of the commutating capacitors will not be discussed here. The input resistance...
Function Generator, capacitance and inductance meter
This site contains complete schematics and code for a 68HC11 based frequency counter, square wave synthesizer, sine wave synthesizer, programmable filter, capacitance and inductance meter, with a digitalker speech synthesizer output. Project specifications are given below.
Two channel frequency synthesizer
This instrument is a one or two channel frequency synthesizer. DC to 35 MHz frequency with 0.1 Hz resolution. +16 to -48 dBm signal level with 0.1 dB resolution. adjustable phase between the 2 channels with 11.25 degree resolution. pushbutton and knob control over user settings; knob acceleration for frequency adjustment. TTL-into-50-ohm sync...
Zener Diode checker
Many times we have found itself in the necessity to use a Zener diode and cannot to know the voltage of operation. Many times we cannot read the characteristics or the type that is written on her. In this case, but in different we can also use the circuit of Fig.1. The T1, D1 and C1 they constitute a system of half-wave rectification. If push...
Transistor and diode tester
The design shown will test PNP and NPN transistors, diodes and SCRs both "in-situ" (equipment of course de-energised) and also by direct connection to a stand-alone component. It is a simple GO/NOGO test which can identify diode and transistor action and will indicate diode polarity and transistor type PNP/NPN, if this is unknown. The CD4093...
Servo tester with PIC12F675
This is a simple servo tester which will comprehensively test the capabilities of almost any modern servo. It has two pushbuttons, CENTRE and SWEEP and a potentiometer which works as follows: - CENTRE Does exactly that, centers the servo, afterwards the potentiometer determines position. - SWEEP Sweeps the servo back and forth at a rate...
Decade resistor box
This device was designed to use two generic-patterned, pre-made, pre-drilled circuit boards that are available from Radio Shack, and other places. Parts consist of: two generic pre-etched and pre-drilled PCBs (printed circuit boards), 136 precision 1%, 1/2-Watt metal-film resistors (46 values), seven 1P10T rotary switches, seven knobs, two...
A simple SWR meter first needs a calibration to Uv = 100 % (forward power). When switching over to Ur (reflected power) the SWR is indicated. This procedure has to be repeated every time a change is made to the transmit power, antenna tuner or frequency etc. With the help of the following circuit one can read the SWR directly without repeating...
Thermal Power Meter
After one has built a QRP transmitter, it would be interesting to know the exact amount of output power. Without a power meter the peak to peak voltage Vss is measured at an 50 ohm resistance (dummy load) with the available oscilloscope. Now the power rate can be calculated according to the formula P = V x V / R. For V the effective voltage...
AGC / S-Meter
You can build an automatic gain control AGC for the superhet receiver with only a few additional components. The first AGC circuit is more universal. It is suitable for audio amplifiers with dual op amps like TL072, TL082, NE5532 and the broadband amp NE592 too. The second circuit is only suitable for AF amplifiers with dual op amps because it...
RF power and VSWR meter
The Inter-Power SWR-5 - upper right - "isn't worth a penny". Got it from a mate to use with a beacon, but I burnt it out with only 3.5-4W morse signal on 70cm. Removed the bridge and installed my own pick-up line (suggested by LA8OJ) and now it is fb for VHF/UHF. The old Hansen, Reace or whatever make "SWR-meter from 1968 (from J. B. Lowe) or...
Decibel-o-meter and white noise generator
Noise level measured into 75ohm 3.1kHz BW using Siemens D2006 level meter: -80dBU (77.5mV) from zero to 1MHz and drops 3dB on 17MHz. Decrease the first coupling capacitor (68nF) to 10nF to increase the lower limit to 50kHz. The amplifier is copied from one of LA7MI's constructions, combined with a general audio amplifier. A noise level was...
Audible Milliohmmeter with 555
This project uses a four-point resistance measurement process also known as the Kelvin method. This procedure uses a current source to determine the value of an unidentified resistance. A constant current flows through the unknown resistance and the voltage drop across it is measured. Note that the current source and voltage measurement wires...
LCD Car Accelerometer
The circuit is drawn for measurement of acceleration from 1000 mg until + 1000 mg. It can be placed in kantra'n the car and be supplied from the sheath of electric lighter. The circuit includes one indicative LED and a screen LCD. The measurement of acceleration becomes with the use of IC from Analog Devices, the ADXL202. The particular element...
AVR LCD Microcontrolled Oscilloscope
A few months ago as I was surfing on the net, I saw an oscilloscope based on PIC18F2550 microcontroller and a KS0108 controller based graphical LCD. That was Steven Cholewiak's web site. I had never seen before so amazing microcontroller-only oscilloscope. That was realy impressive circuit, so I decided to design something like that but in C...
The circuit is powered by the receiver's pack, the current drain is low, specially if compared to drain of servos. U1a VZ2 and Q1 are the CURRENT source of the sensor VZ2 is temperature compensated, use the listed component except for Q1 there you can use any pnp silicon transistor, resistor must be metal oxide 2%(better) or 5%. R4 must be...
Mini Oscilloscope schematic
Probably the best advantage is its very small size and the fact that it can run off the power supply of the circuit being tested. Although it has a low frequency range, it can still be used for most circuits. Its poor resolution will still allow for most waveforms to be visualized. This was pretty much the judges' own assesment of Katz's...
Barometer with Sensor Motorola MPX4115
This design uses a Motorola MPX4115 Silicon Pressure Sensor, a Dallas Semiconductor DS2438 Smart Battery Monitor (to perform 1-Wire analog to digital conversion), an operational amplifier, a voltage regulator, a diode, and several resistors and capacitors. The circuit requires an additional power source other than that of the 1-Wire network. The...
Telephone call meter circuit
In this circuit, a simple calculator, in conjunction with a COB (chip-on-board) from an analogue quartz clock, is used to make a telephone call meter. The calculator enables conversion of STD/ISD calls to local call equivalents and always displays current local call-meter reading. The circuit is simple and presents an elegant look, with...
A simple test circuit to fault find audio and radio equipment. Can be used to inject a square wave signal, rich in harmonics, or used with headphones as an audio tracer. A single pole double throw sitch is used to switch between inject and trace modes. The diagram is drawn in trace mode, the earpiece being connected to the collector of the last...
MIDI tester circuit
Sometimes when experimenting with different soundcards and MIDI interfaces it is useful to see if there is some data going in MIDI interface. This can be easily tested with this adapter, which converts the midi signals to visible light pulses. Just the circuit and plug it to the MIDI output of your computer. When computer sends any midi data...
Capacitor internal resistor meter
The design presented here works by applying a 50kHz, 200mV square wave to the capacitor under test, in series with a 10 Ohm resistor. The AC voltage appearing across that resistor is measured and displayed on a meter. So the whole thing is nothing else than a simple ohmmeter that uses ultrasonic AC for measurement instead of the usual DC used by...
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)...
Digital Volt and Amp Meter
The PIC Microchip Processor must be programmed before it will function as a Volt & Amp meter. There are many internet sites and PIC programmers that you can use. I used a Microchip MPLAB ICD 2 during the project. You might need to made changes to the circuit to accommodate a different type of programmer, do read the programmers instructions...
Frequency Meter Circuits
VU Meter Circuits
Ultrasonic distance finder circuit
The circuit described here uses ultrasonic oscillations and operates based on the propagation velocity of these oscillations in the air. Thus, we can easily determine the distance of two points if the time within which the wave travels this distance is measured. There are three main categories of distance measurement methods in use: a) By...
Simple Metal detector circuit with CD4030
Sometimes the precious metals are hidden too deep and are not detected except with complicated devices. In many cases, however, small pieces of precious metal buried near the surface can be detected by relatively simple means. Everyone is very attractive to find something potentially valuable, hidden a few centimeters below the soil. So many...
Fully automatic watering circuit for flower pots
Many times for various reasons we forget or can not water the plants that we have in our homes. And many humidity sensors units just notify us with a beeping sound or with a flashing light, that the pot needs watering. But what if we are away from home? This circuit comes as a solution to this problem. Depending on humidity of the pot at...
Simple deep searching metal detector circuit
The principle behind a metal detector is really very simple. Proof of this is the circuit that follows, in which it proves that the construction of a metal detector can be done in the minute, with few components that we find very easily everywhere. With the circuit of this metal detector, it is possible to detect a metal coin in depth of 90 to...
Sub-Harmonic Bass Converter for Electric Guitars
The sub-harmonic bass generator is a sound producing unit for guitars. The sound it produces looks very much like that of the bass guitar. The octave generator is sometimes quite unusual since it does not produce any of the usual ways of coloring the sound, such as filtering or distortion. Instead, a frequency division system produces outputs...
Echo Depth Sounding Sonar for Boats
In the past the sounding (sea bottom measurement) was done with the "bullet", that is, with a heavy lead object that the seamen plucked into the sea hung from a calibrated rope. As soon as the "bullet" reached the bottom, the depth appeared directly from the calibration of the rope. This arrangement still exists in some yachts. The big...
100W HiFi Audio Amplifier Circuit
This Amplifier was designed to have the following specifications: Distortion less than 0.1% at full power of 100W even at 20KHz. Power has to be attributed to an extended bandwidth. The output transistors must be protected against short circuits. The power supply must be symmetrical so that no electrolytic capacitors are needed at the outlet....
Plant-Pot Water Level Indicator Circuit
A series of LEDs serve to alert the gardener when plants need water. Using two conventional digital integrated LEDs and a series of LEDs, we make a very useful device for gardening. The device detects the amount of water in the pot and alerts the grower. The circuit of the device is shown in Figure 2. The water detection is made from the bottom...
Analogue Sound Preasure dB-Meter Circuit
The best human ear can capture sounds from 20Hz to 20KHz. These limits are known to be the broadest that can exist. Normally the normal limits range from 100Hz to about 13KHz and depend on the age and health of the individual. We for our measurements and to have a good accuracy we will get the limits of 20Hz to 20KHz. A sound to be heard does...
Digital Signal Integrity
Interconnection and Timing of Digital Circuits
CMOS Circuits Tutorial