Total schematics: 1063
Last updated: 16-May-2001

Alarms and security related

• Intermittent alarm generator
  
• Burglar alarm
  
• Moisture alarm
  
• Fridge door alarm
  
• Proximity alarm
  
• Electronic lock
  
• Door knob alarm (PDF)
  
• Water seepage alarm (PDF)
  
• Micro-power over temperature alarm (PDF)
  
• 5 Zone alarm circuit
  
• Miniature loop alarm
  
• Gate alarm circuit
  
• Perimeter monitor
  
• Digital combination lock
  
• Touch activated alarm system
  

Audio filters

• 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
  
• Akerberg-Mossberg (AM) Second Order Bandpass inverting
  
• Deliyannis Second Order Bandpass I inverting
  
• Deliyannis Second Order Bandpass II inverting
  
• KHN (Non-Inverting Input) Second Order Bandpass inverting
  
• Multiple Feedback (MFB) Second Order Bandpass I inverting
  
• Multiple Feedback (MFB) Second Order Bandpass II inverting
  
• Tow-Thomas (TT) Second Order Bandpass inverting
  
• Twin-T Second Order Bandpass inverting
  
• Berka-Herpy (BH) Second Order Bandpass non-inverting
  
• Fliege Second Order Bandpass non-inverting
  
• KHN (Inverting Input) Second Order Bandpass non-inverting
  
• Mikhael-Bhattacharyya (MB) Second Order Bandpass non-inverting
  
• Sallen-Key (SK) Second Order Bandpass non-inverting
  
• Akerberg-Mossberg (AM) Second Order Notch inverting
  
• KHN (Non-Inverting Input) Second Order Notch inverting
  
• Berka-Herpy (BH) Second Order Notch non-inverting
  
• Fliege Second Order Notch non-inverting
  
• KHN (Non-Inverting Input) Second Order Notch inverting
  
• Mikhael-Bhattacharyya (MB) Second Order Notch non-inverting
  
• Sallen-Key (SK) Second Order Notch non-inverting
  
• Twin-T Second Order Notch I non-inverting
  
• Twin-T Second Order Notch II non-inverting
  
• First Order Highpass III inverting
  
• First Order Highpass IV inverting
  
• First Order Highpass I non-inverting
  
• First Order Highpass II non-inverting
  
• Akerberg-Mossberg (AM) Second Order Highpass inverting
  
• KHN (Inverting Input) Second Order Highpass inverting
  
• Multiple Feedback (MFB) Second Order Highpass inverting
  
• Berka-Herpy (BH) Second Order Highpass non-inverting
  
• Fliege Second Order Highpass non-inverting
  
• KHN (Non-Inverting Input) Second Order Highpass non-inverting
  
• Mikhael-Bhattacharyya (MB) Second Order Highpass non-inverting
  
• Sallen-Key (SK) Second Order Highpass I non-inverting
  
• Sallen-Key (SK) Second Order Highpass II non-inverting
  
• Twin-T Second Order Highpass non-inverting
  
• First Order Lowpass III inverting
  
• First Order Lowpass I non-inverting
  
• First Order Lowpass II non-inverting
  
• Akerberg-Mossberg (AM) Second Order Lowpass inverting
  
• KHN (Inverting Input) Second Order Lowpass inverting
  
• Multiple Feedback (MFB) Second Order Lowpass I inverting
  
• Multiple Feedback (MFB) Second Order Lowpass II inverting
  
• Bach Second Order Lowpass non-inverting
  
• Berka-Herpy (BH) Second Order Lowpass non-inverting
  
• Fliege Second Order Lowpass non-inverting
  
• KHN (Non-Inverting Input) Second Order Lowpass non-inverting
  
• Mikhael-Bhattacharyya (MB) Second Order Lowpass non-inverting
  
• Sallen-Key (SK) Second order Lowpass I non-inverting
  
• Tow-Thomas (TT) Second Order Lowpass non-inverting
  
• Twin-T Second Order Lowpass non-inverting
  

Audio power amplifiers

• 100W Amplifier
  
• 18W Audio amplifier
  
• 25W MOSFET amplifier
  
• Headphone amplifier
  
• Portable headphone amplifier
  
• 2W amplifier
  
• 8 watt audio amp
  
• 20W Amplifier
  
• 50W Amplifier
  
• Two transistor audio amplifier
  
• Personal stereo audio amp
  
• Headphone amplifier
  
• 1.5W Audio amplifier
  
• Low-level audio amp
  
• 10W amplifier
  
• 80W amplifier
  
• LM383 12V 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
  
• Microphone amplifier
  
• RIAA phono amplifier
  
• 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

• Analog Tachometer for Gasoline Engines
  
• Headlight On reminder with Light
  
• Flashing High Intensity LED 3rd Brake Light
  
• Speed limit alert
  
• Portable CD Player Adapter For Car
  
• Car battery charger
  
• Wireless Auto Tachometer
  
• Electronic auto stethoscope
  
• Turn signal alarm
  
• Motorcycle turn-signal system
  
• Cigarette lighter 9V adaptor
  
• Headlight reminder
  
• Breath Alcohol Tester controlling a car ignition system
  
• 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

• TempSentry temperature sensor technical info and schematics
  
• Datalogger based on 68HC11
  
• Analog input section based on AD9220
  
• Digital remote thermometer
  
• Light direction sensor
  
• 12-Bit ADC interface
  
• Digital thermometer
  
• Compost temperature and moisture monitor
  
• Rain detector
  
• Air flow detector
  
• Air flow detector
  
• Strain gauge sensor
  
• 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
  
• Inclinometer using ADXL05
  
• Water-level sensor
  

Games and fun stuff

• Big Mouth
  
• GameBoy Camera Parallel Port Interface
  
• PSX controler to PC MIDI converter
  
• GameBoy Cart Programmer
  
• Pine Racecar Victory Judge
  
• Electronic coin tosser
  
• Electronic craps game
  
• First response monitor
  
• 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
  
• DIT shutterglasses controller
  

Infrared based schematics

• IR remote control system for PC
  
• IR Receiver (Amplitude Modulated IR)
  
• IR Transmitter for Audio (Amplitude Modulated IR)
  
• IR remote control
  
• Infrared body heat detector
  
• Stereo IR audio receiver
  
• General purpose IR receiver
  
• Wireless IR headphone transmitter
  
• Wireless IR headphone receiver
  
• 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
  
• Cheap 40KHz clock
  
• Stable 40KHz clock
  
• Serial driven IR remote control
  
• IR remote transponder
  
• Infrared gate detector
  
• Infrared relay with relay output
  

Laser related power supplies and data transmission

• Laser power supply
  
• Laser transmitter/receiver
  
• Pulsed double-heterostructure laser driver
  
• IR Laser light detector
  
• Light beam receiver for laser pistols
  
• 12V supply for He-Ne laser
  
• Laser diode transmitter
  
• 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

• 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
  
• Winking LEDs
  
• LED flashing light
  
• LED initials
  
• LED chaser
  
• 7 Segment LED Counter
  
• LED Flasher
  
• LED pulser with audible output
  
• IR Illuminator
  
• Flashing Christmas LED display
  
• ICL7660 LED flasher
  
• 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 Audio VU Meter
  
• LM3909 LED flasher
  

Lighting

• 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
  
• Disco style Strobe Light
  
• 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

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

Microcontroller based

• 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
  
• 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
  
• MiniLOGGER V1.0
  
• 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
  
• PIC controlled DDS VFO, 0 to 6 MHz
  
• PIC16F84 line following robot
  
• Embedded controller based on MC68HC11F1
  
• PIC16F84 mechanically scanned clock
  
• EPROM burner
  
• 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
  
• Generate video signals in real-time using a PIC16F84
  
• PIC Project #1 - RS232 to I2C Interface
  
• Talking YODA project (PIC16C84)
  
• PIC16F84/PIC16F87x-In-System-Programmer
  
• PIC16F84 Based Morse Code Reader
  
• 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
  
• PIC16C84 VT-52 Emulator for Linux
  
• Temperature controlled based on AT89CX051
  
• 2-wire LCD interface using PIC16CF84
  
• 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
  
• Picxie 2 - 8x8 Animated LED Signboard (PIC16F84) Picxie 2 - 8x8 Animated LED Signboard
  
• PIC-FC1 Frequency Counter
  

Misc audio (also see Music, Amplifiers, Preamp)

• Frequency shifter
  
• A Schottky-based Saw-to-Tri converter
  
• Saw to triangle converter
  
• Improved saw to triangle converter
  
• Voltage controllable LFO
  
• White noise generator
  
• Low Power Op-Amp - Audio Amp (Intercom)
  
• 555 Tone Generator (8 Ohm Speaker)
  
• 3 Transistor Audio Amp (50 milliwatt)
  
• Low Frequency Sinewave Generator
  
• Horror movies sound effects
  
• Sound amplifier
  
• Temperature sensitive oscillator
  
• Old-fashioned siren effect
  
• Simple VOX circuit
  
• Audio mixer circuits
  
• Audio oscillator circuits
  
• Simple 4-watt AF amplifer
  
• A self-tuning AF filter for CW
  
• SSB AF Filter
  
• Audio level indicator
  
• Room noise detector
  
• Amplifier timer
  
• Bell ring generator
  
• Amplified ear
  
• Precision audio millivoltmeter
  
• Voice record/playback using ISD 1000A
  
• Audio Graphic Equaliser
  
• FET audio mixer
  
• Microphone mixer
  
• Tone control
  
• Digital volume control
  
• Sound level meter
  
• CMOS IC audio oscillator
  
• Electronic siren
  
• Two-tone siren
  
• Underwater microphone
  
• Code practice oscillator
  
• Noise generator
  
• Electronic whistle
  
• 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
  
• Warbler
  
• 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
  

Miscellaneous schematics

• Discrete Set/Reset Flip Flop
  
• Monostable Flip Flops (one shot)
  
• Discrete Bistable Flip Flop
  
• Chaos generator
  
• Simple BFO metal detector
  
• Build Your Own Digital Setting Circles For Your Astronomical Telescope
  
• Electric field disturbance monitor
  
• CW Practice/transmission monitor
  
• A simple CW keyer for paddle keys
  
• Plant watering watcher
  
• Capacitance sensor
  
• Whistle responder
  
• Nocturnal animals whisker
  
• 12V DC electronic door chime
  
• Random noise generator
  
• Hardware random bit generator
  
• Fantastic Atom Expander
  
• Black Light
  
• Computerize Your Room/Home
  
• Flash slave trigger
  
• A Visual CW Zero Beating Aid
  
• A two-way Morse practice set
  
• Basic op-amp circuits
  
• Electronic fish lure
  
• Ultrasonic sound receiver
  
• Experimental data transmitter for fiber optics
  
• Experimental fiber optic receiver
  
• Ion detector
  
• Darkness monitor
  
• Electroscope
  
• Simple event counter
  
• Geiger counter
  
• Light detector
  
• Short-circuit beeper
  
• LM 1800 FM stereo decoder
  
• Glitch detector
  
• MAX924 bar-graph level gauge
  
• Ultrasonic generator
  
• Negative ion generator
  
• ELF Monitor
  
• 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
  
• How to build a tesla coil
  
• 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
  
• 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

• LED traffic lights
  
• R/C Receiver <-> Joystick Port Interface for Flight Simulators
  
• Proportional Radio Control of models
  
• Two-tone siren
  
• HEXBOT robot
  
• Alf: The Robotic Matchbox car
  
• PICar
  
• 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
  
• Two tone train horn
  
• Radio Control Battery Backup
  
• Glow Plug driver for model engines
  

Motor and general control circuits

• 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
  
• Light/dark detector
  
• Pulse Width Modulation DC Motor Control
  
• Stepper motor controller
  
• Touch switch
  
• 12V Sump Pump Control
  
• Transistor relay driver
  
• Latching relay driver
  
• Relay delay circuit
  
• Touch switch
  
• Low voltage DC motor speed controller
  
• Flashing neon christmas lights
  
• Three input first response monitor
  
• Switch-on delay circuit
  
• Electronic thermostat
  
• LM3911 temperature controller
  
• Programmable light-activated relay
  
• 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
  
• 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 (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
  
• Opto-isolated MIDI cable
  

PC related schematics

• I2C printer port adaptor
  
• RS232C Level Converter
  
• Isolated Full Duplex RS232C Interface
  
• PC Serial Port Receiver
  
• Parallel Port Relay Interface Circuit
  
• ISA 8-bit output card
  
• PC based 7-segment rolling display
  
• Parallel print capture system
  
• PC serial port receiver
  
• Parallel port relay interface
  
• 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
  
• Parallel port interface box
  
• 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
  
• 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
  
• SmartCard PC emulator
  
• 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
  

Personal data assistant interfaces and projects

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

Power supplies and control (see also Lighting)

• Power supply provides +5VDC regulated, +10VDC unregulated and 7.5VAC
  
• 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
  
• Basic increase in DC voltage
  
• Power Tool Torque Control
  
• DC-DC converter
  
• A Bench PSU (0-15v 0-3A)
  
• Easy bench PSU
  
• 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
  
• 12V battery capacity tester
  
• NE555 Low Voltage Battery Disconnect Circuit
  
• 13.5KV power supply
  
• Kirlian device supply
  
• LM317 adjustable power supply
  
• LTC1265 Nicad charger
  
• Single cell lithium battery charger
  
• Smart battery charger
  
• Battery charge indicator
  
• Lead acid trickle charger
  
• 12B Battery condition indicator
  
• 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
  
• 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/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
  
• Nicad Battery Discharger/Capacity Indicator
  

Radio-frequency schematics (also see Transmitters)

• Simple Op-Amp Radio
  
• TRF AM Receiver circuit
  
• Crystal radio
  
• Automatic message sender for CB
  
• RF Sensing relay driver
  
• Vibrating pocket bug detector
  
• 2MHz RF Oscillator
  
• 50-150MHz Overtone Oscillator
  
• NASA TURFTS - TDRSS User RF Test Set
  
• Remote powered antenna pre-amplifier
  
• 10K RF probe
  
• IF amplifiers
  
• VHF 144MHz to HF 14MHz Transverter
  
• VHF harmonic oscillator (or QRP VHF FM TX) LO for transverter
  
• Modify a cheap MW radio for 1.8MHz CW/SSB
  
• Direction finding system
  
• An HF (15khZ UPWARDS) DC receiver
  
• One transistor hf regen receiver.
  
• Modify a cheap MW to cover any HF band
  
• Synthesized HF receiver
  
• TBA120 NBFM/FSK/RTTY RX for HF/VHF
  
• TDA7000 VHF WB FM RX
  
• Receivers for HF and VHF USING ZN414
  
• 10W HF Power Amplifier (linear)
  
• 500W linear HF amplifier.
  
• Step VFO
  
• A wide B/W 3 watt QRP HF linear amplifier
  
• A phasing method SSB exciter
  
• 500mW HF Linear Amplifier using 2N2222
  
• Generic VHF Power Amplifiers
  
• The Baycom packet modem
  
• Simple CW filters for homebrew QRP receivers
  
• 10.7MHz (455KHz) TTL FM demodulator
  
• G8TGL RTTY Teleprinter Terminal Unit
  
• The HamComm RTTY/CW/ASCII modem/Interface
  
• CMOS AF/RF Synthesizer (37Hz - 4MHz)
  
• HF/VHF PCB VSWR bridge
  
• 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
  
• UHF oscillator
  
• Economoy short-wave radio
  
• Linearized RF detector
  
• Two-band radio
  
• Shortwave conveter for scanners
  
• FM Bug
  
• AM Radio
  
• Toroidal coil RF shortwave receiver
  
• Crystal radio
  
• 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
  
• Four Channel Wireless Transmitter and Receiver
  
• Wireless event receiver
  
• Talking receiver
  
• Wireless motion detector
  
• 418MHz Control RX/TX
  
• 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
  
• Receiver
  
• 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
  

Solar-powered schematics

• Sun tracking circuit for solar arrays
  
• Solar power recharger
  
• Solar power supply
  
• 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

• 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
  
• Phone in use circuit
  
• Digisound ring modulator
  
• Incoming call indicator
  
• Ringing Phone Light Flasher
  
• Phone Busy Indicator
  
• FM Telephone Bug
  
• Cut Phone Line Detector
  
• Simple Phone Tap
  
• Telephone Hold Button
  
• Telephone Recorder
  
• Telephone recording circuit
  
• 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
  
• Hands-free telephone
  
• Using old phones as an intercom
  
• Phone line to audio
  
• Phone recorder
  
• Telephone tap
  
• Telephone controlled night light
  

Test equipment schematics

• AC Line Current Detector
  
• Triangle and Squarewave Generator
  
• Tri-Waveform Generator
  
• JFET crystal testing oscillator
  
• Grid Dip Oscillator circuit and how to use it
  
• Voltage probe
  
• Live line 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)
  
• Audible continuity tester
  
• Wire tracer
  
• Signal generator for signal tracer
  
• Electronic level
  
• Digital volt meter
  
• Adjustable continuity tested
  
• 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
  
• 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
  
• Continuity tester 2
  
• Continuity tester
  
• Logic probe
  
• 220V wiring detector
  

Timing, oscillators etc.

• 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
  
• Staircase wave generator
  
• 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
  
• Long period timer
  
• 555 time delay circuit
  
• Low frequency clock
  
• 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)

• Micro Power AM Broadcast Transmitter
  
• FM Beacon Transmitter (88-108 MHz)
  
• Portable 40W CW transmitter
  
• Spark-gap transmitter
  
• Wireless microphone
  
• A 3m (100 MHz) small bug
  
• Basic FM Transmitter
  
• One valve CW transmitter (Battery)
  
• 250mW HF bands CW TX
  
• Two Valve CW transmitter (Mains)
  
• LM317 LF HF bands transmitter idea
  
• 5-Watt HF bands CW transmitter
  
• VHF FM Wireless Microphone (v4)
  
• VHF FM Wireless Microphone
  
• High Power VHF FM Wireless Microphone (v5)
  
• Cigar-box transmitter
  
• A simple VHF FM 2-metre transmitter
  
• 2000 watt joke transmitter (spark gap)
  
• QRP SSB HF transmitter
  
• FM transmitter
  
• Two Valve 40m CW Transmitter
  
• Frequency agile 80m CW QRP transmitter
  
• 80 metre DSB transmitter
  
• One Valve CW transmitter
  
• Wireless microphone
  
• XTAL locked tone transmitter
  
• AM oscillator for wireless microphones
  
• Wireless microphone
  
• 1W 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
  
• 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