There are 175 circuit schematics available in this category. Click here for all circuit diagrams. Last circuit added on Thursday, 30 July 2015.

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CircuitCategoryDate AddedOK?Votes 
RCM710 electronic scale, technical manual including schematicTestApr 12, 20011
Sensor to display, built with thermistor, 12-bit ADC, 89S52 and LED displayTestMar 25, 2009-2
Thermistor Thermometer: LCD versionTestMar 25, 20090
Ground Fault IndicatorTest 0
Sound pressure level meterTestSep 23, 20090
True RMS Watt MeterTestSep 23, 20090
The u-counter, a PIC based programmable frequency meter (PDF)TestOct 05, 20090
Ultra-simple Voltage ProbeTestJun 26, 20090
Wire tracerTest -1
IR Remote Control TesterTestJul 05, 20121
Digital Voltmeter using ICL7107TestSep 17, 20090
Beeper to find short circuitsTestOct 19, 20090
Led display digital Voltmeter using ICL7107TestSep 17, 20090
MOSFET transistor testerTestNov 05, 20090
Oscilloscope testing module (huntron circuit)TestNov 10, 20090
Logic probeTestOct 19, 20090
Pulse Reading Logic ProbeTestOct 19, 20090
Stereo Test Tone GeneratorTestOct 21, 20090
Continuity Tester based on 4 x 2N3904 and 1 x 2N3905 transistorsTestOct 19, 20090
Audible Logic Probe based on LM339 operational amplifierTestOct 19, 20090
Single chip digital voltmeter using ICL7129TestNov 05, 20090
Latching Continuity Tester to help find intermittent faults, has quite a few innovative featuresTestOct 19, 20090
Linear Resistance MeterTestOct 19, 20090
XTal Tester for testing quartz crystals based on a pair of BC550C PNP transistorsTestOct 19, 20090
Self-powered Fast Battery-Tester - Tests 1.5 to 15 Volt cellsTestSep 17, 20091
Microphone polarity tester circuit diagranTestApr 14, 2010-1
Low-Drift High-Impedance JFET DC VoltmeterTestJan 08, 20140
Resistor decade boxTestAug 14, 20020
Simple test equipment to buildTest 0
RF Power Meter for the QRP measures up to 25 wattsTest 1
Dip Oscillator for HFTest 0
High Impedance VoltmeterTestSep 10, 20060
Servo Motor Test Circuit (LM555)Test 0
Frequency counter based on PIC16F628 and LCD displayTestJun 19, 20110
220V live wire-in-wall scannerTestMar 23, 20030
Test oscillator that generates sinewaves, squarewaves, and triangle wavesTestFeb 20, 2013-1
PPMScope DIY oscilloscope with 1MHz sampling rate and Windows softwareTestFeb 20, 20130
KD1JV Digital SWR / Power MeterTestApr 12, 20140
Low Power Antenna Analyzer and ATU Tuning AidTest 0
Fixed Frequency "Tuner Dipper"Test 0
Universal frequency counter & voltage meterTestOct 07, 20090
ESR MeterTestMay 17, 20021
Line Output / Flyback transformer testerTestMay 17, 20020
PCB board tester and RF detector circuir diagramsTestFeb 09, 20100
Alarm circuit to remind you to turn off your DMM (digital multimeter)TestJan 31, 20100
Function generator based on 555 timer and three 2N2222 transistorsTestFeb 05, 20100
Multi-trace scope display that allows up to 4 channels to be viewed on a single oscilloscope channelTestFeb 26, 20100
DDS from 1-60 MHz with built-in amplifier and variable output level using Analog Devices AD9851Test 0
Isolated oscilloscope probeTestMay 16, 20100
Superprobe handheld test device based on a PIC16F870TestMay 24, 20100
Build an inexpensive Hall effect GaussmeterTest 0
Design for a slightly more expensive GaussmeterTest 0
VCR head amplifier testerTestMay 25, 20120
Conrad Electronics MM3610D multimeter cable pinoutTestSep 10, 20060
Audio MillivoltmeterTestApr 14, 20100
Microphone Circuit Test OscillatorTestApr 14, 20100
Distortion analyser circuit diagramTestApr 14, 20100
The ESP SIM (Sound Impairment Monitor)TestApr 14, 20100
Linkwitz Cosine Burst GeneratorTestApr 14, 20100
Amplified field strength meter / RF snifferTestApr 14, 20110
3 in one tester (audio, tone generator, diode/circuit tester)Test 0
In-circuit electrolytic capacitor checkerTestMar 27, 20090
Logic probe with pulserTestMar 27, 2009-1
Electric field & leakage detectorTestAug 12, 20010
Simple Polarity TesterTestSep 01, 20090
20kV Digital High Voltage MeterTestNov 16, 20100
Eight simple power supplies for your workbench (mainly vacuum tube based)TestApr 10, 20140
Filter Choke AnalyzerTestApr 10, 20140
Vacuum Tube Grid Leak Detector: Needs an AmplifierTestApr 10, 20140
A Load Box for testing power suppliesTestApr 10, 20140
Low resistance adapter for a DMM (digital multimeter)TestApr 10, 20140
Vacuum Tube Plate Detector: Needs an AmplifierTestApr 10, 20140
Miniature SWR / RF power meter circuitTestFeb 15, 20140
Schematics and C code for a PIC frequency counter operating up to about 50 MHz (7 segment)Test 0
Schematics and C code for a 0-5V PIC LCD volt meterTest 0
Schematics and C code for a PIC frequency counter operating up to about 50 MHz (LCD)Test 0
Not So Tiny Power Meter - Measures power consumption for entire apartment Not So Tiny Power MeterTestFeb 21, 20130
LED based transistor tester LED based transistor testerTestOct 05, 20120
TTL pulse counter/logic probeTest 0
Quickie servo tester for testing servo motors (based on Atmel AT90S2343)TestAug 17, 2009-1
Frequency and capacitance meterTestJan 26, 20010
Transistor TesterTestNov 13, 20101
Wire Tracer (Receiver)TestNov 13, 20100
Wire Tracer (Transmitter)TestNov 13, 20100
Elecraft XG2 receiver test oscillator (PDF)TestSep 13, 20060
Contactless Mains Voltage IndicatorTest 0
Mini tester: Handles continuity testing, resistor testing, capacitor testing and diode testingTest 0
Precision audio millivoltmeterTestFeb 21, 20050
PIC16F84 based diode testerTestFeb 21, 20050
Continuity tester using transistorsTestFeb 21, 20050
Latching continuity tester using 4093TestFeb 21, 20050
Linear Resistance MeterTestFeb 21, 20050
Crystal tester circuit diagramTestFeb 21, 20050
Capacitance meterTestFeb 21, 20050
Digital voltmeter (DVM)TestFeb 21, 20050
Transistor tester using 555 timer and 4027TestFeb 21, 20050
Function generator based upon 8038 waveform generator ICTestFeb 21, 20050
Picoammeter circuit schematic with 4 ranges using CA3420TestFeb 21, 20050
Beeper to find short circuits (continuity tester)TestFeb 21, 20052
MOSFET tester for N-type MOSFET transistorsTestFeb 21, 20050
Inductive meter adapter to measure inductance using a frequency counterTestFeb 21, 20050
Crystal tester that covers a range of 32kHz to 24MHzTestFeb 21, 20050
Oscilloscope testing module (Huntron circuit) that shows Lissajous patternsTestFeb 21, 20050
Logic probe with 7-segment display based on 74LS00 and 74LS47TestFeb 21, 20050
Simple light sensor adapter for oscilloscopeTestJan 26, 20010
TDR cable reflection tester (Time Domain Reflectometer)TestSep 21, 20060
Soft Power On Tester for AmplifiersTestJan 29, 20100
TXTVb - 70cm ATV Test Generator (PDF)Test 0
BCD readout frequency counterTestAug 18, 20090
LCD Frequency CounterTestAug 18, 20090
Miniscope - simple all-valve 1-inch CRT oscilloscopeTestOct 25, 20090
Panel Mounting Radio Frequency CounterTestAug 18, 20090
Simple Frequency CounterTestAug 18, 20090
Heathkit signal generator user manual and circuit diagramTestOct 25, 20090
Spectrum analyzer Mk 1TestAug 18, 20090
Spectrum analyzer Mk 2TestAug 18, 20090
TinyScope - simple all-valve 1-inch CRT oscilloscopeTestOct 25, 20090
Z80 controlled Viscometer projectTestAug 18, 20090
Field Strength Meter (FSM) covers 2Mhz - 1Ghz with peak reception at 3-200MhzTest 0
UHF signal generatorTest 0
VHF signal generatorTest 0
-20 dB Couplers for use with a with a spectrum analyzer or other sensitive detectorTest 0
-20 dBm, 14.060 MHz Precision Signal SourceTest 0
Precision VXO for Crystal Characterization & MatchingTest 0
Return Loss BridgeTest 0
Digital pH MeterTestMay 19, 20150
PIC Harmonic Distortion Meter for measuring the quality of AC supplyTestMay 19, 20150
Cheap oscilloscope and sensor probes for physics experiment in schoolTestMay 19, 20150
DigiThermo - a laboratory instrument that measures time and temperatureTestApr 22, 20140
Mini oscilloscope based on PIC18F4620 and standard 16x2 text LCD display moduleTestJun 27, 20100
AD9850 DDS daughterboardTestSep 21, 20060
Signal Tracer and InjectorTestSep 13, 20060
TDS/PPM Meter for measuring of the amount of salts in a solutionTestMar 29, 20090
Homebrew signal generator tunable from 3 to 30 MhzTestOct 08, 20090
Precision Frequency MarkerTest 0
Simple Inductance MeterTest 0
VCR Tuner Based RF Spectrum Analyzer SchematicTestSep 21, 20060
LCD frequency counter (PIC16F84)TestNov 29, 20020
Simple electronic S meterTest 0
Standalone LED testerTestNov 02, 20100
Fluke 8010 / 8012 InterfaceTestSep 25, 20090
UTP Cable TesterTestSep 25, 20090
10Hz - 100KHz D.D.S. Function GeneratorTestSep 21, 20060
555 Timer IC Tester circuit diagramTestJan 26, 20011
555 go / no-go tester circuit diagramTestJan 08, 20020
Battery Tester for 1.5 and 9VTest 0
Continuity tester V2 circuit diagramTestJan 26, 20010
Continuity tester circuit diagramTestJan 26, 2001-1
Logic probeTestJan 26, 20010
Simple pH Meter Circuit, A Low Cost Adapter for Your Digital VoltmeterTestNov 02, 20100
Magic Eye Tube WavemeterTestMay 19, 20150
TTL Pulse Reading Logic ProbeTestSep 21, 20060
Stereo Test Tone GeneratorTestSep 21, 20060
Octopus Curve TracerTestMay 19, 20150
Pulse Reading Logic ProbeTestJan 26, 20010
LC meter with LCD display for readoutTest 0
An ESR Meter For Electrolytic Capacitors (and Low Ohms Meter)TestJun 24, 20150
Build your own Q Meter projectTestJun 24, 20150
A Simple RF Probe For Your DVMTestJun 24, 20151
An RF Voltmeter for Transceiver ServicingTestJun 24, 20150
Medium and Very High Quality Two Tone Generators for Transceiver TestingTestJun 24, 20150
Highly sensitive and selective Field Strength Meter systemTestApr 14, 20110
Wide dynamic range Field Strength Meter mark ITestApr 14, 20110
Wide dynamic range Field Strength Meter mark IITestApr 14, 20110
Digital Wattmeter, measures from nanowatts to kilowatts using AD8307, PIC16F876, LCD DisplayTest 0
SWR Bridge 1 to 1000 Mhz (1GHz)Test 0
Field strength meter for the 137 kHz bandTestMay 01, 20040
Multi wire cable tester that handles up to eight conductorsTestNov 27, 20020
Connection tester for checking solder joints and other connectionsTestNov 27, 20020
EMF field probe (electromagnetic field probe) covering up to 100kHzTestJan 26, 20010
Function generator based on 8038PCD function generator ICTestJan 26, 20010
Logic probe based on CMOS 4001 chipTestJan 26, 20010
Zener diode tester based on a 555 timerTestJan 26, 20010
Accurate Digital LC Meter based on a PIC16F84TestFeb 20, 20130
Pulse Generator And Signal Tracer Circuit DiagramTestJul 22, 20150