Alarms and security related schematics

Intermittent alarm generator Burglar alarm Moisture alarm
Fridge door alarm
Ultrasonic remote control & alarm system
Door knob alarm (PDF)
Water seepage alarm (PDF)
Micro-power over temperature alarm (PDF)
Personal silent alarm system
5 Zone alarm circuit
Miniature loop alarm
Gate alarm circuit
Perimeter monitor
Digital combination lock
Touch activated alarm system

Audio filter schematics

Active 2nd Order Filters
RC Notch Filter (Twin T)
3KHz low-pass filter plus audio amp (PDF)
"A" Weighting Filter For Audio Measurements
Multiple Feedback Bandpass Filter

Audio power amplifier schematics

100W Amplifier
18W Audio amplifier
25W MOSFET amplifier
Headphone amplifier
Portable headphone amplifier
2W amplifier
8 watt audio amp
20W Amplifier
50W Amplifier
100W Audio amplifier
100W RMS Amplifier
2-Channel Power Amplifier
Push-Pull Class A Amp using type 5687 dual triodes
Push-Pull Class A 2A3 Stereo Amp
Single Ended Class A2 SV811-10 Stereo Amp
Audio amplifier output relay delay
HeadBanger Headphone Amp
2W Amplifier
TDA2030 8 Watt amplifier
16 Watt amplifier
8 Watt amplifier
20 Watt Class-A Power Amplifier
El-Cheapo - A Really Simple Power Amplifier
Single Chip 50 Watt / 8 Ohm Power Amplifier
Hi-Fi Headphone Amplifier
100W Guitar Amplifier
Death of Zen (DoZ) - A New Class-A Power Amp
Soft-Start Circuit For Power Amps
Thermo-Fan To Keep Your Amp Cool
Audio Amp Output Power Limiter
55W (Originally 75W) Power Amplifier
300W Subwoofer Power Amplifier
20 Watt / Channel Stereo Power Amplifier

Audio preamp circuits

Phono preamp
Simple microphone preamplifier
Phono Preamp
Simple microphone preamplifier
ECM Mic preamp
Hi Fi preamp
Electret mic amplifier
Audio preamplifier
Audio preamp
Low impedance microphone amplifier

Automative, car and motorcycle schematics

Analog Tachometer for Gasoline Engines
Headlight On reminder with Light
Flashing High Intensity LED 3rd Brake Light
Car clock
Car message display
Car interval wiper
Safety indicator light
Speed limit alert
Portable CD Player Adapter For Car
Car battery charger
Wireless Auto Tachometer
Headlight reminder
Breath Alcohol Tester controlling a car ignition system
Parking sonar
Simple Car Preamplifier and Artificial Earth
Interface between GM's 5 Volt 8192 baud ALDL data stream and a PC serial port
3rd brake light
12V to 9V car coverter
Car Nicad charger
Economy radar detector

Data acquisition and data logging schematics

TempSentry temperature sensor technical info and schematics
Datalogger based on 68HC11
Analog input section based on AD9220
Light direction sensor
12-Bit ADC interface
Digital thermometer
Compost temperature and moisture monitor
Rain detector
Web-based thermometer project
Honey Bee counter (PDF)
Capacitance type liquid level measurement (PDF)
Digital PC Oscilloscope
Serial Port A/D-converter
Centronics port D/A converters and low-pass filter
Water-level sensor

Games and fun stuff (schematics)

Big Mouth
GameBoy Camera Parallel Port Interface
PSX controler to PC MIDI converter
GameBoy Cart Programmer
Memory game
Project: NES to Atari 2600 controller interface
Pine Racecar Victory Judge
PowerGlove Interface
GameBoy Schematic
GameBoy LCD schematic
GameBoy Power & Cartridge schematic
GameBoy ROM+RAM+MBC1 Cart Schematic
GameBoy MBC1 circuit equivalent
Super GameBoy schematic
Quiz show indicator
Bingo!!! (on your tv)
Slot car TV cronograph
DIT shutterglasses controller

Infrared based schematics

IR remote control system for PC
IR Receiver (Amplitude Modulated IR)
IR Transmitter for Audio (Amplitude Modulated IR)
Universal IR-Remote Lamp Controller
IR remote control
40KHz light receiver (PDF)
40KHz TV-VCR repeater (PDF)
Infrared remote transponder
Build an Infrared night scope
Decoding IR Remote Controls
IR detector
PC IR Remote Control
An Ambient-Light-Ignoring Infrared Active Motion Detector
IR Ranging
Pyroelectric Infrared Sensor
Simple IR transmitter circuit
Simple infra-red detector
IR remote control extender
IR remote control tester
Infrared repeater
40khz IR Tester
555 timer 40khz IR Oscillator
IR detector / emitter
Implementing Infrared Object Detection
Infrared gate detector
Infrared relay with relay output

Laser related power supplies and data transmission

Laser power supply
Laser transmitter/receiver
20MHz VCSEL 3mW laser test circuit (PDF)
10MHz to 20MHz laser light detector (PDF)
Micro-power 40KHz burst laser diode driver (PDF)
40KHz laser burst detector (PDF)
Modulated laser diode tester (PDF)
Experimental laser data link

LED related schematics

Winking LEDs
LED flashing light
LED initials
1.5 Volt LED Flashers
AC Line Powered LEDs
Astable Multivibrator
9 Second Digital Readout Timer
9 Second LED Relay Timer
16 Stage Bi-Directional LED Sequencer, other sequencer and flaser circuits
10 Stage LED Sequencer
28 LED Clock Timer
Fading Red Eyes
Two Transistor LED Flasher
16 Stage Bi-Directional LED Sequencer
Expandable 16 Stage LED Sequencer
LED Photo Sensor Circuit
LED chaser
7 Segment LED Counter
1.5V LED flasher B (PDF)
Low current LED flasher (PDF)
1.5V LED flasher A (PDF)
Flashing LED advertising badge (PDF)
Pulsed LED test circuit (PDF)
Low battery voltage flasher (PDF)
Adjustable flashing LED
LED Mood Light
LED Audio VU Meter
LM3909 LED flasher
Picxie 2 - 8x8 Animated LED Signboard

Lighting schematics

Disco style Strobe Light
Varying Brightness AC Lamp
12 Volt Lamp Dimmer
120VAC Lamp Chaser Using Solid State Relays
Flashing Neons (NE-51 / NE-2)
Sequencing Neons (NE-51 / NE-2)
Touch Activated Lamp
220V Flashing lights
Coutesy lamp
Bedside lamp timer
TRIAC light dimmer
12VDC Fluorescent Lamp Driver
Strobe light
Adjustable Strobe Light
5W Fluorescent light intensity modulator (PDF)
1W Fluorescent lamp night light (PDF)
Electronic night light
LED Mood Light
LX-800 Lighting system
Xenon Strobe Light
Lamp flasher/dimmer
PWM light bulb regulator

Medical and health related schematics

Radiation Dosage-Rate Meter
Heartbeat monitor
Cranial Electrotherapy Stimulator
Automated crib lights
Joigging timer
Tan timer
Muscular Bio-stimulator
Simple lie detector
The ESP SIM (Sound Impairment Monitor)

Microcontroller based schematics

Z80 core #1- Z80 CPU and memory (PDF)
Z80 core #2- Z80 CTC and SIO
Z80 core #3- RS-232 drivers for the SIO
RS485-Version of the SAB80C535-Microcontrollerboard
PC IR receiver based on PIC16F84
AT89C2051/4051scanning 7-segment display and keypad
AT89C2051/4051 Driving dot LED
AT89C2051/4051stepper motor interface
AT89C2051/4051connecting dumb terminal
Simple RS232C Level Converter using Transistors
C-52 EVB Robot Controller
Mains clock controller using AT89C2051
AT89C2051/4051 Easy-Downloader
AT89C51/52/55 Easy-Downloader
PIC16F84 programmer
PIC16F84 miniature real-time controller
Isolated RS232 for PIC16F84
PIC16F84 debugging terminal
Atmel 89C Series Flash Microcontroller Programmer
AT89C2051 real-time controller
PIC12C508 Night-light saver
AT89C2051 Night light saver
Atmel 8051 Flash Based-Microcontroller Programmer
AT89C2051 Digital thermometer and clock
12C508 Smart Lock
Build a PIC controlled DDS VFO, 0 to 6 MHz
PIC controlled DDS VFO, 0 to 6 MHz
TCP/IP stack and WWW server in a PIC16F84
PIC16F84 line following robot
50 MHz frequency counter, voltage meter & SWR/PWR indicator
Embedded controller based on MC68HC11F1
RDS Encoder - digital part
Freign vocabulary recollector
Embedded system to send e-mails (small TCP/IP stack)
Speaking clock using PIC & ISD device
Speaking doorbell using PIC & ISD device
Whistle detector using 8-pin PIC
PIC16F84 mechanically scanned clock
68HC11 stepper motor control
Serial to parallel converter using the AT89C2051
AT89C2051 serial COMs to LED driver
101 AT Keyboard to ASCII Decoder using 68HC705J1A MCU
DTMF tone decoder using Basic Stamp
A Scenix (and PIC) Programmer
Long-period watchdog timer
PIC16F84 Range Finder Project
Generate video signals in real-time using a PIC16F84
PIC Project #1 - RS232 to I2C Interface
Dual PIC16C84 prototype board
Talking YODA project (PIC16C84)
Microcontroller interface for 5KW microwave oven
PIC16F84 Based Morse Code Reader
Interfacing piezo elements to a microcontroller
PICADC - a free, PIC based "intelligent" A/D converter
AT89C2051 line-follower robot
PIC16F84 sound controlled Christmas lights
Convenient PIC module
Spread spectrum transceiver controlled by PIC
68HC11 based RDS decoder
PIC16C84 VT-52 Emulator for Linux
Temperature controlled based on AT89CX051
2-wire LCD interface using PIC16CF84
PIC16F84 Serial I/O-expander with PicBasic
PIC R/C Servo Controller
Microprocessor RS-232 Reset
A PIC-Based Keyboard Emulator
ScanMate audio activated recorded
Remote control encoder/decoder with PIC16C620 & PIC12C508
Electronic door codelock with PIC16F84
Automatic door opener with PIC12C508
Infra/radio remote control transmitter/receiver with PIC
Automatic door opener (PIC)
Picxie 2 - 8x8 Animated LED Signboard (PIC16F84) Picxie 2 - 8x8 Animated LED Signboard
PIC-FC1 Frequency Counter
10 tricks for interfacing to the PIC16C508
Interfacing the PIC16C508
PIC 5x7 display
Analog to digital conversion notes
Multi-chip programmer

Misc audio (also see Music, Amplifiers, Preamp)

A Schottky-based Saw-to-Tri converter
Saw to triangle converter
Improved saw to triangle converter
Voltage controllable LFO
White noise generator
Horror movies sound effects
Sound amplifier
Temperature sensitive oscillator
Old-fashioned siren effect
Simple VOX circuit
Low Power Op-Amp - Audio Amp (Intercom)
555 Tone Generator (8 Ohm Speaker)
3 Transistor Audio Amp (50 milliwatt)
Low Frequency Sinewave Generator
Audio level indicator
Room noise detector
Amplifier timer
Bell ring generator
Amplified ear
Precision audio millivoltmeter
A Stereo Digital Volume Control based on the CS3310
Voice record/playback using ISD 1000A
Audio Graphic Equaliser
Analog VU meter
Voltage controlled amplifier
Audio graphic equaliser
Intercom preamp
FET audio mixer
Microphone mixer
Tone control
Digital volume control
Sound level meter
CMOS IC audio oscillator
Very loud beeper (PDF)
Digital noise generator (PDF)
Condenser microphone hookup
Phase shifter
Paradoxical Sound Syntheizer
Audio line isolator
Dynamic microphone to electret microphone input
Line level signal to microphone input adapter
Simple two line output combiner
Electret microphone powering circuits
Use amplifier phono input as line level input
Speaker signals to line level inputs
Spring reverb unit
Sine wave generator
3-Band equalizer
6-Input mixer
Doorphone intercom
Stereo line driver
Audio notch filer
Peak reading audio level meter
Tone control
Electronic canary
Improved PL tone decoder
Magnetic cartridge amplifier
LM358 preamp
Sound detector
Tone detector
Tone generator
Voltage Controlled Panner
Low Noise Microphone Preamplifier
Bridging Adapter For Power Amplifiers
Simple Surround Sound Decoder
Simplest Ever Amplifier Bridging
Stereo Width Controllers
Power Amplifier Clipping Indicator
Phono Preamps For All
Digital Delay Unit For Surround Sound
Parametric And Sub-Woofer Equaliser
High Quality Sound Mixer
Loudspeaker Protection and Muting
Direct Injection Box for Recording & PA Systems
Minimalist Discrete Hi-Fi Preamp
Signal Detecting Auto Power-On Unit
Load Sensing Automatic Switch
Amplifier thermal protection
Active Sub-Woofer and Controller
Balanced Line Driver & Receiver
VU And PPM Audio Metering
Variable Amplifier Impedance
Linkwitz Cosine Burst Generator
Low Noise Balanced Microphone Preamp
Fast Audio Peak Limiter
Subwoofer Equaliser
Audio output level meter

Miscellaneous schematics

Chaos generator
Simple BFO metal detector
Electromagnetic Levitator
Build Your Own Digital Setting Circles For Your Astronomical Telescope
Electric field disturbance monitor
Discrete Set/Reset Flip Flop
Monostable Flip Flops (one shot)
Discrete Bistable Flip Flop
Plant watering watcher
Capacitance sensor
Whistle responder
Nocturnal animals whisker
12V DC electronic door chime
Random noise generator
Hardware random bit generator
Analog pulse counter
Analog opto-isolator
Pulse width modulators (PWM)
Pulse width to voltage converter
Fantastic Atom Expander
Black Light
Computerize Your Room/Home
Flash slave trigger
A Visual CW Zero Beating Aid
A two-way Morse practice set
Tesla power receiver
Basic op-amp circuits
Supervisory Control And Data Aquisition project (for Home Automation and Security)
Ion detector
1uS light pulse descriminator plus F to V converter (PDF)
Broadband 2MHz optical fiber receiver (PDF)
Modulated light received (PDF)
1uS light pulse receiver plus post amp (MISC)
Broadband 5MHz optical fiber receiver (PDF)
High-speed light receiver (PDF)
Basement doorbell beeper (PDF)
Time to dust indicator (PDF)
Low-power optical interrupter (PDF)
Simple nitrogen spark generator (PDF)
Ultrasonic transducer oscillator circuit
Build logic gates using discrete parts
Jacob's Ladder
Variety of quick designs
Fogger smoke machine
Electric field disturbance monitor
Dual comparator forms temperature-compensated proximity detector
Electromagnetic field detector
Ultrasonic dog whistle
An Inexpensive X-ray Machine
Magnetic levitation circuit
Ultrasonic switch
Very basic circuits
Bat detector
FCTS Project
Morse Code Beacon Keyer
Lightning Activated Camera Shutter Trigger
Electronic Dazer
Morse Code Practice Keyer 1
Morse Code Practice Keyer 2
741 Light Sensor
Fluid level detector
Full-duplex doorphone
Scaling ADXL50 accelerometer output

Model and remote control schematics

R/C Receiver <-> Joystick Port Interface for Flight Simulators
LED traffic lights
Two-tone siren
HEXBOT robot
Alf: The Robotic Matchbox car
A Low Cost Thermal Peak Detection Charger
A Miniature High-Rate Speed Control with Brake
An On/Off Motor Control with Brake
0-10V control for RC servos
Simple flashing light circuit
Simple flashing light circuit
A dual alternating flashing light circuit
Simple flashing light circuit
A dual tandem flashing light circuit powered by a 9 volt battery
Simulate the Gyralite (dual flashing headlights).
Simple train detector using ambient light and a photocell
Simple charge rate monitor
Deluxe charge rate monitor
"CLONEPAC" memory module for Futaba 8UAF/8UAP
Battery pack discharger
Plane locator
Plane locator 2
Battery low voltage alarm
Battery low voltage alarm 2
Ultimate battery low voltage alarm
Building an RF Remote Control System
Two tone train horn
Radio Control Battery Backup
Glow Plug driver for model engines

Motor and general control schematics

Electronic Thermostat Relay Circuit
Interfacing 5 volt CMOS to 12 volt loads
Light Activated Relay
CMOS Toggle Flip Flop With Relay(CD4013)
555 Timer Monostable Circuit Using Pushbutton
Current loop interface
Switching solenoid driver
Modular relay system
Light/dark detector
Pulse Width Modulation DC Motor Control
Stepper motor controller
Touch switch
12V Sump Pump Control
Pushbutton one-shot and latch (PDF)
Charge coupled bi-directional power MOSFET relay (PDF)
Finger touch activated switch (PDF)
Machine vibration triggers hour meter (PDF)
Solid state relay (PDF)
Line-powered Xenon flash transmitter (PDF)
9V Xenon photoflash controller (PDF)
AC switching with TRIAC from TTL
Control 120VAC relay with TTL
Driving a relay with a CPU
Power-line Appliance Controller
Combination-controlled, fully customizable RF remote control
Thermoelectic controller (scriptable thermometer)
Stepper motor positioner
SN754410 Dual Motor Driver Board
Temperature monitor
Cold activated switch
Voltage comparator switch
Dark activated switch
DC Push Button Motor Control Circuit
Light detector
Sound operated switch
Touch Switches
Detect fan failure with a single transistor
Constant Temperature Circuit
PWM DC Motor Speed Control
Solenoid starter
CO2 controller for planted tanks
Light activated relay

Music related schematics (also see Audio)

Drum machine
Simple MIDI-to-CV converter
Sounds effects unit
ETI 603 Sequencer
Synthesizer schematics
Peak-reading meters
Octave screamer
Optical Theremin - electronic musical instrument
Spring reverb unit
Metronome and pitch generator
Mini metronome
Simple colour organ
Guitar fuzz effect
8 note tune player
Colour (Sound) Organ
Transisor organ
Audible metronome
Visual metronome
Simple line mixer
Simple MIDI tester
Electronic metronome
Guitar Reverb Pedal
Guitar Tremolo Unit
Spring Reverb Unit For Guitar
Ultra Simple Bass Guitar Compressor
Vox AC30 Guitar Amplifier Simulator
Guitar Vibrato Unit
Musical Instrument (Expandable) Graphic Equaliser
D.C. Mixer for music synthesizers

PC related schematics

I2C printer port adaptor
RS232C Level Converter
Isolated Full Duplex RS232C Interface
ISA 8-bit output card
PC based 7-segment rolling display
Parallel print capture system
Modem Rockwell RCV336/ACF model V1433VQR ext.
Genius Mouse schematics
PC serial port receiver
Parallel port relay interface
ISA 48 I/O digital card
Parallel (Printer) Port Interface
RS-232 line monitor and loopback cables
A Serial Infrared Remote Controller
Interfacing 16x2 character :LCD to parallel port
8254 Timer and Counter Board
Serial to ECP interface
A PC-Based LowFER Frequency Synthesizer
General purpose 48-bit ISA parallel I/O card
4-channel 8-bit analog-to-digital converter for PC
Printer port ADC
Parallel port ADC based on MAX147
Analog Signal Acquisition for PC Printer Port
More accurate PC/AT clock
Getting power from RS-232 interface
Barcode scanner
PC thermometer
Parallel port servo controller
Connect two CD-ROM drives to one soundcard
Headphone driving circuit for soundcards
Get power out of PC parallel port
Null Printer Adapter
PC speaker volume control circuit
How to get power from PC to your circuits
RS-232 surge protection
Simple RS-232 serial port buffer circuit
Get power out of PC RS-232 port
Sound Blaster Microphone Preamplifier
Sega 3D glass interfacing circuits
Convert Atari-style joystick to PC joystick port
Fake Joystick circuit
Using the joystick port as general purpose input
Connect other circuits to PC joystick port
Schematic of a standard PC joystick
Simple PC SmartCard reader
Fax to modem interface
DC-DC Power Supply from car 12V battery to PC motherboard
Linux Infra-red Remote Control (LIRC)
Compter microphone
Laptop Computer Serial Port Power Booster
HamComm Interface
Hi-Fi PC Speaker System
IDE hard-disk interface for Amiga 500
Parallel port ADC/DAC
Parallel port ADC using ADC0804
High speed 20MSPS ADC interface
9-pin null modem cable
24-bit parallel port interface with 8255 for Commodore computer
24-line PC digital interface (PDF)
SPDIF-interface to AudioPCI

PDA interfaces and related schematics

SHARP palm-top/hand-held to RS232 serial converter
Casio organiser hardware
Casio datalogger

Power supplies and control schematics

Power supply provides +5VDC regulated, +10VDC unregulated and 7.5VAC
Basic increase in DC voltage
Power Tool Torque Control
Generating Negative 5 Volts from 9 Volt Battery
LED Battery Condition Indicator
LM317 Variable Voltage Regulator
LM317 Regulator With Pass Transistor
High Current Regulated Power Supply
Simple Variable Voltage Source
Variable 3 - 24 Volt / 3 Amp Power Supply
2 watt switching power supply
Variable Voltage and Current Power Supply
Low Power DC to DC Converter
Constant Current Battery Charger
Variable DC power supply
Using the 78xx Series Voltage Regulators
6V to 12V Converter
Tesla coil / HV generator
12VDC To 120VAC Inverter
High Current Power Supply
Dual Polarity Power Supply
High Voltage High Current Power Supply
Transformerless Power Supply
Fixed Voltage Power Supply
Voltage Inverter
Voltage Inverter
1A Variable Regulated Power Supply
Negative voltage generator
12V battery capacity tester
NE555 Low Voltage Battery Disconnect Circuit
Power reminder beeper (PDF)
Unplugged power cord alarm
Machine power loss beepter (PDF)
HV supply: 12VDC in, 12KV out
Generating -5VDC from +5VDC
Filtering PC bus POWER
Bidirectionall power inverter
Adjustable power supply using LM317
Simple +5V power supply circuit
12V 30A power supply
Dual regulated power supply
Fuse blown indicator
Gyrator circuit
Variable power supply
Nicad battery charger
Regulated 12V supply
Unregulated power supply
12 volt battery monitor
12 volt power supply
5 volt power supply
Battery voltage monitor
LM3914 battery monitor
Multiple voltage power supply
Voltage doubler
Voltage inverter
PWM Motor Speed Controller / DC Light Dimmer
PWM Motor/Light Controller
Low Power LED Voltmeter
PWM Motor/Light Controller
PWM Motor/Light Controller variants
Low Power LED Voltmeter
Temperature Controlled NICD Charger
Simple Capacitance Multiplier Power Supply For Class-A Amplifiers
Simple DC Adapter Power Supply
Variable Dual Lab Power Supply
Charger for gel lead acid batteries
12V to 120VAC inverter
Nicad Battery Discharger/Capacity Indicator

Radio-frequency schematics (also see Transmitters)

CW RECEIVER 40/80 meter CW receiver
TRF AM Receiver circuit
Receiver building blocks
Crystal radio
Automatic message sender for CB
RF Sensing relay driver
Vibrating pocket bug detector
2MHz RF Oscillator
50-150MHz Overtone Oscillator
Simple Op-Amp Radio
HF Linear RF power amplifier
100W HF Linear AMP
3W FM Transmitter
Crystal radio
Op-Amp Radio
Car radio tunes the Amateur Bands
Crystal set that requires no antenna
80m Direct Conversion Receiver
A compact L-match ATU for portable use
Morse Adaptor for your VHF/UHF FM rig
An end-fed antenna, L-match coupler and resistive bridge for HF
AM Broadcast Band Regenerative Receiver
50 MHz to 146 MHz Converter
Hear Amateurs on your Shortwave Radio!
Compact 20 14 MHz direct conversion receiver
Hear Amateurs on your FM Radio!
RF actuated CW monitor
LF to HF Converter
Super 80 ultra-simple SSB receiver for 3.5 MHz
The MRX-40 Mini Receiver
Phase Shift Radio Direction Finder
Bug detector
175KHz inductive pulse receiver (PDF)
200-400 MHz voltage controlled oscillator
Icom CT-17 Logging & Control Interface Level Converter
AM/FM/SW active antenna
RF Sniffer <.5 to >500 MHz
Frequency Synthesizer
Four Channel Wireless Transmitter and Receiver
Wireless event receiver
Talking receiver
Wireless motion detector
418MHz Control RX/TX
2N2222 40 Meter CW/DSB Transceiver
AM receiver
Field strength meter
MW preamplifier
Simple field strength meter
4 band double-tuned preselector
ZN414 AM receiver
ZN414 shortwave receiver
Phased lock loop schematic
SOP direct conversion receiver
Simple UHF dummy load
30m direct conversion receiver
Popcorn direct conversion receiver
40m direct conversion receiver
80m direct conversion receiver
R-399-A Communications Receiver
136 kHz direct conversion receiver
How to Build a 300MHz AM, RF Remote Control System
RF Modem Robotics Project
Smooth Tone Clickless CW Sidetone Generator
Variety of receiver converter projects
One transistor FM receiver
42 Mc Band to 88 Mc Band (retrofit converter) Project
50MHz Assistant (Preamp & Power Amp.)
Bug detector
Basic RF oscillator
Superregenerative 27MHz receiver
Radio Control Electric Switch
56K RF Modem
80M ARDF direction finder

Solar-powered schematics

AA battery solar charger
Solar Panel Charge Controller / Low Voltage Disconnect Circuit
Solar Panel Current Meter
Solar Charged LED Flashlight
AA battery solar charger
Solar Panel Charge Controller / Low Voltage Disconnect Circuit
Solar Panel Current Meter
Solar cell Nicad charger

Telephone and intercom related schematics

Phone in use circuit
Digisound ring modulator
Incoming call indicator
Telephone Ring Generator Using 60Hz Power Transformer
Telephone Ring Generator Using Switching Power Supply
Telephone In-Use LED Indicator
Telephone In-Use Relay Circuit
Telephone Audio Interface
Ringing Phone Light Flasher
Phone Busy Indicator
FM Telephone Bug
Cut Phone Line Detector
Simple Phone Tap
Telephone Hold Button
Telephone Recorder
1-line telephone status indicator (PDF)
Line in use indicator (PDF)
4-line telephone status indicator (PDF)
Caller ID decoder
Telephone in use light
Detecting a telephone RING
Phone In-Use Light
Phone to audio interface
Phone Off-Hook Indicator
'phone rang' indicator light
Phone Line to Audio
Phone in-use
Telephone Line Monitor
Use old phones as an intercom
Phone-In-Use indicator
Hold function for Telephone
Digital/Standard Phone Line Tester
Universal telephone hold
Talking phone dial monitor
Telephone line simulator
Telephone privacy adapter
Telephone ringing circuits
Simple circuit to connect telephone equipment to audio mixer
Cut phone line detector

Test equipment schematics

Tri-Waveform Generator
JFET crystal testing oscillator
ESR Meter
Line Output / Flyback transformer tester
AC Line Current Detector
Triangle and Squarewave Generator
Voltage probe
Live line detector
Electric field & leakage detector
Simple polarity detector
RCM710 Electronic Scale
3 - 12 MHz Signal Generator
Some simple test equipment to build
RF Power Meter for the QRPer
Dip Oscillator for HF
Two Tone Audio Oscillator (use for SSB tests)
Simple pH meter
Temperature compensated pH meter
pH meter with calibration
LASER/LED light output intensity meter (PDF)
Frequency and capacitance meter
Simple light sensor adapter for oscilloscope
Time Domain Reflectometer (TDR)
EMF field probe
Function generator
Logic probe
Zener diode tester
Signal tracer & injector
Pulse Reading Logic Probe
Pink Noise Generator for Audio Testing
Audio Millivoltmeter
Audio Test Oscillator
Full Featured Transistor Tester
Opamp Design and Test Board
Microphone Circuit Test Oscillator
Distortion Analyser
Self Oscillating Amplifier for Distortion Testing
Build a Magnetic Field Immunity Tester
555 Timer IC Tester
555 go / no-go tester
12V Lead-Acid Battery Monitor
Continuity tester 2
Continuity tester
Logic probe
220V wiring detector
In-circuit electrolytic tester
PIC logic probe with pulser

Timing, oscillators etc. (schematics)

Staircase wave generator
1 Second Time Base From Crystal Osc.
Power-On Time Delay Relay Circuit
Low Voltage , High Current Time Delay Circuit
Power-Off Time Delay Relay Circuit
Generating a Delayed Pulse With a dual 555 Timer
1KHz Sinewave generator
Timed beeper
Weign Bridge generator
Time Delay Relay
Time Delay Relay
Wide-swing Variable Crystal Oscillator
Circuit that momentarily closes a pair of contacts at long intervals
Line powered 60Hz clock generator (PDF)
Micro-power pulse generator (PDF)
Darkroom camera shutter timer
Divide by 1.5 counter (PFD)
High-output square wave generator (PDF)
D Flip-flot one-shot circuits (PDF)
Clock divider
Clock doubler
CMOS oscillator
Crystal 32.768KHz CMOS Oscillator
Crystal oscillator
Cheap 40KHz clock
Stable 40KHz clock
'Rounding Off' a square wave
Switch debounce using 555
Square wave to sine wave converter
Micropower pulse generator (PDF)
Push Button Switch Debouncer
Square wave oscillator
Clock generator
555 Timer Tutorial + Circuits

Transmitter schematics (also see RF)

Portable 40W CW transmitter
Spark-gap transmitter
Wireless microphone
A 3m (100 MHz) small bug
Basic FM Transmitter
Micro Power AM Broadcast Transmitter
FM Beacon Transmitter (88-108 MHz)
FM transmitter
Two Valve 40m CW Transmitter
Frequency agile 80m CW QRP transmitter
80 metre DSB transmitter
One Valve CW transmitter
175KHz inductive pulse transmitter (PDF)
Small Radio Transmitter
FM Telephone Transmitter
Micropower Event Transmitter
FM transmitter
4 transistor transmitter
FM transmitter
Op-amp based FM transmitter
Miniature FM transmitter
Sensitive FM transmitter
Simple RF transmitter
1.5 volt tracking transmitter
Tracking transmitter
Micro Power FM Broadcasting Circuits
Low Power FM Transmitter
30-Meter QRP Transmitter for Morse Code
Miniature FM Transmitter #1
Miniature FM Transmitter #2
Miniature FM Transmitter #3
Light sensing RF transmitter
Micro-Spy with FETs
Micro-Spy with USW
Micro-Spy with TTL

Video related schematics

Audio / video distribution amplifier
Driver for multiple VGA monitors
Closed-Caption Decoder
PIC-Tock video clock
Video signal amplifier
MC1374 based TV transmitter
TV transmitter
Simple TV transmitter
Video signal edge enhancement
Video amplifier
Digital volt meter with video output
Video switcher (PDF)
Video switcher
TV/Radio antenna cable galvanic isolator
S-video to composite video adapter
VGA converter for video projectors and fixed frequency monitors
VGA to TV converter
VGA to PAL and NTSC converter
Do-it-Yourself VGA ro PPrPb Cable
Many video amplifier circuits includiing transmission over UTP (PDF)
Mark II video digitiser
Video digitiser
Audio-video switch