There are 171 circuit schematics available. Last circuit added on Saturday, 30 May 2015.

CircuitCategoryDate AddedOK?
RCM710 electronic scale, technical manual including schematicTestApr 12, 2001
Sensor to display, built with thermistor, 12-bit ADC, 89S52 and LED displayTestMar 25, 2009
Thermistor Thermometer: LCD versionTestMar 25, 2009
Ground Fault IndicatorTest 
Sound pressure level meterTestSep 23, 2009
True RMS Watt MeterTestSep 23, 2009
The u-counter, a PIC based programmable frequency meter (PDF)TestOct 05, 2009
Ultra-simple Voltage ProbeTestJun 26, 2009
Wire tracerTest 
IR Remote Control TesterTestJul 05, 2012
Digital Voltmeter using ICL7107TestSep 17, 2009
Beeper to find short circuitsTestOct 19, 2009
Led display digital Voltmeter using ICL7107TestSep 17, 2009
MOSFET transistor testerTestNov 05, 2009
Oscilloscope testing module (huntron circuit)TestNov 10, 2009
Logic probeTestOct 19, 2009
Pulse Reading Logic ProbeTestOct 19, 2009
Stereo Test Tone GeneratorTestOct 21, 2009
Continuity Tester based on 4 x 2N3904 and 1 x 2N3905 transistorsTestOct 19, 2009
Audible Logic Probe based on LM339 operational amplifierTestOct 19, 2009
Single chip digital voltmeter using ICL7129TestNov 05, 2009
Latching Continuity Tester to help find intermittent faults, has quite a few innovative featuresTestOct 19, 2009
Linear Resistance MeterTestOct 19, 2009
XTal Tester for testing quartz crystals based on a pair of BC550C PNP transistorsTestOct 19, 2009
Self-powered Fast Battery-Tester - Tests 1.5 to 15 Volt cellsTestSep 17, 2009
Microphone polarity tester circuit diagranTestApr 14, 2010
Low-Drift High-Impedance JFET DC VoltmeterTestJan 08, 2014
Resistor decade boxTestAug 14, 2002
Simple test equipment to buildTest 
RF Power Meter for the QRP measures up to 25 wattsTest 
Dip Oscillator for HFTest 
High Impedance VoltmeterTestSep 10, 2006
Servo Motor Test Circuit (LM555)Test 
Frequency counter based on PIC16F628 and LCD displayTestJun 19, 2011
220V live wire-in-wall scannerTestMar 23, 2003
Test oscillator that generates sinewaves, squarewaves, and triangle wavesTestFeb 20, 2013
PPMScope DIY oscilloscope with 1MHz sampling rate and Windows softwareTestFeb 20, 2013
KD1JV Digital SWR / Power MeterTestApr 12, 2014
Low Power Antenna Analyzer and ATU Tuning AidTest 
Fixed Frequency "Tuner Dipper"Test 
Universal frequency counter & voltage meterTestOct 07, 2009
ESR MeterTestMay 17, 2002
Line Output / Flyback transformer testerTestMay 17, 2002
PCB board tester and RF detector circuir diagramsTestFeb 09, 2010
Alarm circuit to remind you to turn off your DMM (digital multimeter)TestJan 31, 2010
Function generator based on 555 timer and three 2N2222 transistorsTestFeb 05, 2010
Multi-trace scope display that allows up to 4 channels to be viewed on a single oscilloscope channelTestFeb 26, 2010
DDS from 1-60 MHz with built-in amplifier and variable output level using Analog Devices AD9851Test 
Isolated oscilloscope probeTestMay 16, 2010
Superprobe handheld test device based on a PIC16F870TestMay 24, 2010
Build an inexpensive Hall effect GaussmeterTest 
Design for a slightly more expensive GaussmeterTest 
VCR head amplifier testerTestMay 25, 2012
Conrad Electronics MM3610D multimeter cable pinoutTestSep 10, 2006
Audio MillivoltmeterTestApr 14, 2010
Microphone Circuit Test OscillatorTestApr 14, 2010
Distortion analyser circuit diagramTestApr 14, 2010
The ESP SIM (Sound Impairment Monitor)TestApr 14, 2010
Linkwitz Cosine Burst GeneratorTestApr 14, 2010
Amplified field strength meter / RF snifferTestApr 14, 2011
3 in one tester (audio, tone generator, diode/circuit tester)Test 
In-circuit electrolytic capacitor checkerTestMar 27, 2009
Logic probe with pulserTestMar 27, 2009
Electric field & leakage detectorTestAug 12, 2001
Simple Polarity TesterTestSep 01, 2009
20kV Digital High Voltage MeterTestNov 16, 2010
Eight simple power supplies for your workbench (mainly vacuum tube based)TestApr 10, 2014
Filter Choke AnalyzerTestApr 10, 2014
Vacuum Tube Grid Leak Detector: Needs an AmplifierTestApr 10, 2014
A Load Box for testing power suppliesTestApr 10, 2014
Low resistance adapter for a DMM (digital multimeter)TestApr 10, 2014
Vacuum Tube Plate Detector: Needs an AmplifierTestApr 10, 2014
Miniature SWR / RF power meter circuitTestFeb 15, 2014
Schematics and C code for a PIC frequency counter operating up to about 50 MHz (7 segment)Test 
Schematics and C code for a 0-5V PIC LCD volt meterTest 
Schematics and C code for a PIC frequency counter operating up to about 50 MHz (LCD)Test 
Not So Tiny Power Meter - Measures power consumption for entire apartment Not So Tiny Power MeterTestFeb 21, 2013
LED based transistor tester LED based transistor testerTestOct 05, 2012
TTL pulse counter/logic probeTest 
Quickie servo tester for testing servo motors (based on Atmel AT90S2343)TestAug 17, 2009
Frequency and capacitance meterTestJan 26, 2001
Transistor TesterTestNov 13, 2010
Wire Tracer (Receiver)TestNov 13, 2010
Wire Tracer (Transmitter)TestNov 13, 2010
Elecraft XG2 receiver test oscillator (PDF)TestSep 13, 2006
Contactless Mains Voltage IndicatorTest 
Mini tester: Handles continuity testing, resistor testing, capacitor testing and diode testingTest 
Precision audio millivoltmeterTestFeb 21, 2005
PIC16F84 based diode testerTestFeb 21, 2005
Continuity tester using transistorsTestFeb 21, 2005
Latching continuity tester using 4093TestFeb 21, 2005
Linear Resistance MeterTestFeb 21, 2005
Crystal tester circuit diagramTestFeb 21, 2005
Capacitance meterTestFeb 21, 2005
Digital voltmeter (DVM)TestFeb 21, 2005
Transistor tester using 555 timer and 4027TestFeb 21, 2005
Function generator based upon 8038 waveform generator ICTestFeb 21, 2005
Picoammeter circuit schematic with 4 ranges using CA3420TestFeb 21, 2005
Beeper to find short circuits (continuity tester)TestFeb 21, 2005
MOSFET tester for N-type MOSFET transistorsTestFeb 21, 2005
Inductive meter adapter to measure inductance using a frequency counterTestFeb 21, 2005
Crystal tester that covers a range of 32kHz to 24MHzTestFeb 21, 2005
Oscilloscope testing module (Huntron circuit) that shows Lissajous patternsTestFeb 21, 2005
Logic probe with 7-segment display based on 74LS00 and 74LS47TestFeb 21, 2005
Simple light sensor adapter for oscilloscopeTestJan 26, 2001
TDR cable reflection tester (Time Domain Reflectometer)TestSep 21, 2006
Soft Power On Tester for AmplifiersTestJan 29, 2010
TXTVb - 70cm ATV Test Generator (PDF)Test 
BCD readout frequency counterTestAug 18, 2009
LCD Frequency CounterTestAug 18, 2009
Miniscope - simple all-valve 1-inch CRT oscilloscopeTestOct 25, 2009
Panel Mounting Radio Frequency CounterTestAug 18, 2009
Simple Frequency CounterTestAug 18, 2009
Heathkit signal generator user manual and circuit diagramTestOct 25, 2009
Spectrum analyzer Mk 1TestAug 18, 2009
Spectrum analyzer Mk 2TestAug 18, 2009
TinyScope - simple all-valve 1-inch CRT oscilloscopeTestOct 25, 2009
Z80 controlled Viscometer projectTestAug 18, 2009
Field Strength Meter (FSM) covers 2Mhz - 1Ghz with peak reception at 3-200MhzTest 
UHF signal generatorTest 
VHF signal generatorTest 
-20 dB Couplers for use with a with a spectrum analyzer or other sensitive detectorTest 
-20 dBm, 14.060 MHz Precision Signal SourceTest 
Precision VXO for Crystal Characterization & MatchingTest 
Return Loss BridgeTest 
Digital pH MeterTestMay 19, 2015
PIC Harmonic Distortion Meter for measuring the quality of AC supplyTestMay 19, 2015
Cheap oscilloscope and sensor probes for physics experiment in schoolTestMay 19, 2015
DigiThermo - a laboratory instrument that measures time and temperatureTestApr 22, 2014
Mini oscilloscope based on PIC18F4620 and standard 16x2 text LCD display moduleTestJun 27, 2010
Mini DDS (direct digital synthesizer) using an Analog Devices AD9832 (12MHz maximum frequency)TestNov 27, 2002
AD9850 DDS daughterboardTestSep 21, 2006
Signal Tracer and InjectorTestSep 13, 2006
TDS/PPM Meter for measuring of the amount of salts in a solutionTestMar 29, 2009
Homebrew signal generator tunable from 3 to 30 MhzTestOct 08, 2009
Oscilloscope / Logic Analyzer based on an ArduinoTestJun 20, 2010
Precision Frequency MarkerTest 
Simple Inductance MeterTest 
VCR Tuner Based RF Spectrum Analyzer SchematicTestSep 21, 2006
LCD frequency counter (PIC16F84)TestNov 29, 2002
Simple electronic S meterTest 
Standalone LED testerTestNov 02, 2010
Fluke 8010 / 8012 InterfaceTestSep 25, 2009
UTP Cable TesterTestSep 25, 2009
10Hz - 100KHz D.D.S. Function GeneratorTestSep 21, 2006
555 Timer IC Tester circuit diagramTestJan 26, 2001
555 go / no-go tester circuit diagramTestJan 08, 2002
Battery Tester for 1.5 and 9VTest 
Continuity tester V2 circuit diagramTestJan 26, 2001
Continuity tester circuit diagramTestJan 26, 2001
Logic probeTestJan 26, 2001
Simple pH Meter Circuit, A Low Cost Adapter for Your Digital VoltmeterTestNov 02, 2010
Magic Eye Tube WavemeterTestMay 19, 2015
TTL Pulse Reading Logic ProbeTestSep 21, 2006
Stereo Test Tone GeneratorTestSep 21, 2006
Octopus Curve TracerTestMay 19, 2015
Pulse Reading Logic ProbeTestJan 26, 2001
LC meter with LCD display for readoutTest 
Highly sensitive and selective Field Strength Meter systemTestApr 14, 2011
Wide dynamic range Field Strength Meter mark ITestApr 14, 2011
Wide dynamic range Field Strength Meter mark IITestApr 14, 2011
Digital Wattmeter, measures from nanowatts to kilowatts using AD8307, PIC16F876, LCD DisplayTest 
SWR Bridge 1 to 1000 Mhz (1GHz)Test 
Field strength meter for the 137 kHz bandTestMay 01, 2004
Multi wire cable tester that handles up to eight conductorsTestNov 27, 2002
Connection tester for checking solder joints and other connectionsTestNov 27, 2002
EMF field probe (electromagnetic field probe) covering up to 100kHzTestJan 26, 2001
Function generator based on 8038PCD function generator ICTestJan 26, 2001
Logic probe based on CMOS 4001 chipTestJan 26, 2001
Zener diode tester based on a 555 timerTestJan 26, 2001
Accurate Digital LC Meter based on a PIC16F84TestFeb 20, 2013