Switching Circuits

Frost Alarm
Dark Activated Switch
Electronic Keypad
Light Detector Circuit
DC Motor Control Circuit
PBS Switch Debouncing Circuit
Remote Doorbell Warning Switch
Electronic Doorbell with Counter
Digital Combination Lock
Electronic Night Light
Sound Operated Switch
Voltage Comparator Switch
DC Motor Reversing Circuit
Voltage Controlled Switch using 555 Timer
Keypad Switch No.2
Electronic Door Release
Intelligent switch
Heat-Sensitive Switch
Washing Machine Motor Controller
Voltage-Based Controller For Switches
Automated Traffic Signal Controller
Automatic Switch For Audio Power Amplifier
Automatic Headlight Brightness Switch
Load Sensing Auto Switch
Solid State Switch for DC Operated Gadgets

Miscellaneous

Flashing Neons (NE-51 / NE-2)
Sequencing Neons (NE-51 / NE-2)
Touch Activated Light
Game Show Indicator Lights (Who's First)
Salt Water Battery
Transistor Schmitt Trigger Oscillator
Car parking system using Microcontroller
Electronic House
Automatic Railway Gate Control
Intelligent Train Engines
Water level indicator and controller
THE SUDOKU SOLVER
Automatic Railway Grade Crossing Flashers
Joy Stick Controlled - Modernized "Toy" Throttle
Laser Pointer Train Detector
Automatic Station Stop Circuit
Plant Watering Watcher - Version II
Water-Level Controller
Staircase Light With Auto Switch-Off
Fire Alarm Using Thermistor
Mobile Cellphone Charger
DIGITAL ENGINE TACHOMETER
Centronics port D/A converters and low-pass filter
Plant Moisture Meter
Room Noise Detector
Heating System Thermostat
Cellular Phone calling Detector
Temperature-controlled Fan
Temperature-controlled 12V dc Fan
Digital Step-Km Counter
Bicycle back Safety Light
Whistle Responder
Jogging Timer
Automatic plant Irrigation (AT89C2051)
Prepaid Energy Meter
Traffic Light Controller

Motor Speed Control

AC Motor Speed Controller
Pulse Width Modulation DC Motor Control
Simple Servo Controller
Simple Two Speed Contactor DC Motor Controller
Stepper Motor Controller
DC motor speed controller
Stepper Motor controller (2)
Auto Control of three phase Induction motor (AT89S52)

Power Supply Circuits :

12VDC To 120VAC Inverter
Automatic Load Sensing Power Switch
Car Battery Charger
Dual Polarity Power Supply
Fixed Voltage Power Supply
High Current Power Supply
High Voltage High Current Power Supply
Power Supply
Machine power loss beepter (PDF)
DC/AC inverter
Variable Dual Lab Power Supply
12v "high" or "low" battery monitor
Electric power controller
Live-line Detector
AC Current Monitor

Robotics

ROBOTIC CAR
Adam - I
Adam - II (micromouse competition entrant)
Optical Mouse Hack - Used in Adam - II
The 1381-based solar engine
555-based solar engine
90S2313 AVR Robot Board
IR Detector for Robot
RF Modem Robotics Project
Small 3-wheel ROBOT with PIC16F84 brain & InfraRed eyes
Line Follower ROBOT
Desktop Line Following Robot
Mini line follower Robot
Fire Fighting Robot (AT89S52)
Line Following Robot (AT89C2051)
PC Based Robot (AT89C2051)

Light Circuits

12V stroboscope
Analogue light controlling desk
Four channel dimmer rack
Mini pocket stroboscope
Simple light bulb flasher
Strobo controller
Stroboscope trigger circuits
12 Volt Lamp Dimmer
12 Volt Lamp Fader (Automatic)
120 VAC Lamp Dimmer (full wave SCR)
2 Wire DC Lamp Dimmer Replaces Rheostats
230 Volt Dimmer
4 Channel dimmer rack
8 Bit Digital Light Intensity Controller
A Ballast that can Be Dimmed from a Domestic (Phase Cut) Dimmer
Circuit Delivers Dimming Control for White LED Driver
8 Photo-Detector Circuit Board
Dark Activated Switch or Porch Light Switch
Dark/Light Activated Relay
Dark-activated 230V Lamp
Dark-activated LED or Lamp Flasher
Day and Night Infrared Detection
10MHz TO 20MHz LASER LIGHT DETECTOR
30KHZ LIGHT RECEIVER AMP
40KHz LASER BURST DETECTOR
40KHz Light Detector with Sunlight Immunity
3v Low Battery Voltage Flasher
9v POWERED XENON PHOTOFLASH Controller
Flashing Rear-End Device For DCC Systems
Flashing-Cum-Running Light
LASER Transmitter/Receiver
PIC Light Chaser
Battery-powered Night Lamp
Bedside Lamp Timer
Emergency Light & Alarm

Wireless Projects

Door Monitor Project
Wireless Weather Station
WMP3 - Wireless Internet Radio Player
MOBILE JAMMER
"Mobile BUG"
Wireless Auto Tachometer
Digital Remote Thermometer
Device control through Bluetooth from Symbian OS Mobiles

Audio Circuits

15 Watt Amplifier
150W MP3 Car Amplifier
24 Watt Class A Amplifier
Buffer Amplifier
Class-A//AB Amplifier
Audio Level Meter
Voice-Over Circuit
Simple 3 Transistor Audio Amp (50 milliwatt)
Improved 3 Transistor Audio Amp (80 milliwatt)
Audio Amplifier for Personal Stereo
Mosfet-Based Preamplifier for FM Radio DXing
Precision Amplifier With Digital Control
22 Watt Audio Amplifier
50 Watt Amplifier
FET Audio Mixer
Guitar Fuzz Effect
Microphone Mixer
Mono To Stereo Synthesizer
Sound Level Meter
Stereo Tube Amplifier
300W Subwoofer Power Amplifier
TDA2030 8 Watt amplifier
Single Chip 50 Watt / 8 Ohm Power Amplifier
Hi-Fi Preamplifier
MASTHEAD PREAMP
100W Guitar Amplifier Mk II
Simple Surround Sound Decoder
High Quality Audio Mixer
Simple Car Preamplifier and Artificial Earth
Loudspeaker Protection and Muting
Minimalist Discrete Hi-Fi Preamp
(Discrete Opamp)
Thermo-Fan To Keep Your Amp Cool
Active Sub-Woofer and Controller
Audio Amp Output Power Limiter
Subwoofer Amp
Audio Auto Shutoff
10W Audio Amplifier with Bass-boost
Automatic Loudness Control
Portable Mixer
Speech Amplifier Box
Mini-MosFet Audio Amplifier

Solar Circuits

Shunt-mode Solar/Wind Charge Controller
Self Powered Solar Box Furnace
Solar Powered Night Light
Solar Powered Reading Lamp
Solar Tracker
Solar Recorder
1381-based Solar Engine
555-based solar engine
Flashing LED-based Solar Engine
The "Miller" solar engine
SCC3 - 12 Volt 20 Amp Solar Charge Controller
Solar tracking System

Radio Circuits

AM Receiver
ZN414 Portable Receiver
2 Transistor FM Voice Transmitter
FM Transmitter
4 Transistor Transmitter
FM Transmitter with Opamp
Band 2 Preamplifier
Superhet AM Broadcast Receiver
AM Broadcast Loop Antenna
Micro Power AM Broadcast Transmitter
FM Beacon Transmitter (88-108 MHz)
Medium-Power FM Transmitter

LED Circuits

1.5 Volt Dual LED Flasher
40 LED Bicycle Light (555 Timer - 6 volt)
28 LED Clock
Two Transistor LED Flasher
LED Photo Sensor Circuit
Fading Red Eyes
LED Traffic Lights
16 Stage Bi-Directional LED Sequencer
AC Line powered LEDs
1.5V LED Flasher VERSION A
1.5V LED Flasher VERSION B
12v Lamp Current Indicator
LED or Lamp Pulser
Dancing LEDs
Fading LEDs
LEDs or Lamps Sequencer
Halloween Flashing-eyes Badge
Light Flasher

Relay Circuits

Relay Toggle Circuit Using a 555 Timer
Relay Toggle Circuit Using a Single Transistor and Push Button
Relay Toggle Circuit Using a MOSFET and Push Button
555 Timer Monostable Circuit Using Pushbutton
Light Activated Relay (toggled)
Photo Electric Street Light
Power-On Time Delay Relay Circuit
Power-Off Time Delay Relay Circuit
Electronic Thermostat Relay Circuit
CHARGE COUPLED BI-DIRECTIONAL POWER MOSFET RELAY
SOLID STATE RELAY REQUIRES ONLY 50uA DRIVE CURRENT
THROUGH GLASS PUSHBUTTON SWITCH
Ultra Low Power Latching Relay Circuit
Universal Flasher using Latching Relay
Water Activated Relay
Time Delay Relay
Time Delay Relay II
Temperature-controlled Fan
Bedside Lamp Timer
Clap Relay
Water Pump Relay Control

Op-Amp Circuits

Op-Amp Basics
2nd Order Opamp Filters
Bandpass Filter (Single Op-Amp)
Low Power Op-Amp - Audio Amp (Intercom)
Op Amp Radio

Timing Circuits

Basic 555 Monostable
5 to 30 Minute Timer
Periodic Timer
Asymmetric Timer
24 Hour Timer
555 Pulse Generator
Repeating Interval Timer
Repeating Timer No.2
LM555 Timers - Circuits and Calculators
Long delay Timer
Hands Off
Bike Light Flasher
Headlight Flasher

Door Bell Circuits

BASEMENT DOORBELL BEEPER
Birdie Doorbell Ringer
Ding-Dong Bell
Door Chime
Doorbell for the Deaf
Electronic Doorbell with Counter
Electronic Canary (Doorbell)
Fix Adds Door-Chime Repeater
Multi-Switch Doorbell with Indicators
Remote Doorbell Warning Switch
Self-Powered Door-Bell Watcher
Two Tone Generator

Medical Electronics / Biomedical Circuits

DS1621 pc thermometer
Electronic Stethoscope
The ESP SIM (Sound Impairment Monitor)
BIOMEDICAL MONITORING SYSTEM (AT89C2051 + TX/RX)