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Circuits designed by David Johnson, P.E.
Last Updated on: Tuesday, October 24, 2017 06:54 AM

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David Johnson's Circuits

from Dave's Circuits, Hobby Circuits & Circuit Solutions

+5v Powered Charge Pump Battery Charger

0.5v Negative Supply

1 Amp Current Injector

1 Watt Fluorescent Lamp Night Light

1.5v LED Flasher Version A

1.5V Touch Activated Switch

10 Amp UL Ground Resistance Tester

10 LED Sequential Flasher using Low Power

10 Second Ultra Lower Power Oscillator

10 Turn Pot Forms Frequency Readout

100ma Current Source

10mhz to 20mhz Laser Light Detector

10Mhz to 20Mhz Light Receiver

120 VAC Low Voltage Alarm

120 VAC Touch Switch

120VAC Under Voltage Tester

125Khz LC Oscillator

125Khz Oscillator from CMOS Inverters

125khz Wireless Smart Key Detector

12kv Power Supply

12v Battery Load Cutout Circuit

12v Battery Voltage Monitor-Expanded Scale 

12v Cooling Fan Thermostat

12v Lamp Current Indicator

12v Light/Dark Lamp Switch

12v to 19v Laptop Power Supply (Concept)

12v Touch Switch Exciter Circuit

12v-24v AC & DC Day/Night Switch

175Khz Inductive Pulse Receiver

175Khz Inductive Pulse Transmitter

18v AC to DC Power Supply

1us Light Pulse Receiver

1uS Light Pulse Receiver + Post Amp

1w Solar Cob LED Light

1W Solar Path Light with COB

2 Line Telephone Line Status Indicator

2 Transistor Oscillators

2.45ghz RF Signal Detector

20 LED Night Light

200Mhz-400Mhz Voltage Controlled Oscillator (VCO)

20ma Current Loop Tester

20Mhz VCSEL 3mw Laser Test Circuit

2-12v Battery Isolator Circuit with a LTC4412

240VAC to 5VDC Power Supply

240VAC Touch Switch

24v NiMH
Battery Charger using a 12v Solar Panel 

2uS Light Pulse Receiver

3 Minute LED Closet Light

3 Volt Low Battery Voltage Flasher

30 LED Night Light

300v Peak to Peak Signal Generator

30Khz Light Receiver Amp

32Khz Ultra Low Power Crystal Oscillator

36-Hour Watchdog Timer

3Khz Low Pass Filter Plus Audio Amp

3-Minute Closet Light

3-Minute Closet Light #2

3v 2hz Oscillator

3v Battery Powered White LED Driver

3v Capacitance Proximity Switch

3v Powered Loud Beeper

3v Sweeping Siren Alarm

4 Line Telephone Line Status Indicator

40Khz Laser Burst Detector

40Khz LED Test Signal Generator

40Khz Light Detector with High Ambient Light Immunity

40KHz Light Detector with Sunlight Immunity

40Khz Light Receiver Amp

40KHz Light Receiver Front-End Circuit

40KHz Limiting Amp

40KHz Modulated Light Detector

40khz TV-VCR Light Source Repeater

40Khz Ultrasound Receiver

40Khz Voltage to Frequency Converter

4-20ma Current Loop Tester

5 Volt Momentary Operation Touch Switch

50/60Hz Sync Generator-Fully Isolated

50Mhz Broad Band Optical Fiber Receiver Version A

555 Timer Forms Simple Circuit PWM Motor Controller

5Mhz Broad Band  Optical Fiber Receiver

5v Capacitance Touch Activated Momentary Switch

5w Fluorescent Lamp Intensity Modulator

6v NMH/NiCd Battery Tester

6V to 24V DC Day/Night Switch

8 Solar Cell LED Light

8-Solar Cell Lithium Ion Battery Charger Version 2

9v Battery Eliminator

9v Battery Voltage Monitor

9v Powered Xenon Photoflash Controller

9V Pulse Generator

9v Solar Panels Converted to 4.5v Panels

AC Current Controls Hour Meter

AC Line Under/Over Voltage Alarm

AC Power Line High/Low Voltage Tester

AC Power Loss Alarm

AC to DC Power Supply requires Low Power

Acceptable Voltage Indictor

Accurate Low Capacitance Meter

Accurate One Shot Pulse Generator

Active AC Power Line Indicator

Active Low Pass Filter Designs

Advertising Badge #1 with Flashing LED

Advertising Badge #2 with Flashing LED

AIR Transparency Monitor, Xenon Flash Receiver

AIR Transparency Monitor, Xenon Flash Transmitter

AIR Transparency Monitor-Pg2

Alarm Beeps when the “Check Engine” Light Turns On

Alarm Sounds At Freezing Temperatures

Alarm sounds when Water is Detected

Alarm-Piezo Device Detects Motion

Alkaline Low Battery Voltage Indicator

Alternating CW & CCW Motor Driver

Amplifier for a Xenon Lamp Flash Detector

Another Very Loud piezo Alarm Beeper

Audio Activated Switch

Audio Amp + 3Khz Filter

Audio Frequency Digital Noise Generator

Automotive Electrical Voltage Indicator

Bad Light Bulb Indicator

Band Drummer’s Microphone Switch

Basement Doorbell Beeper

Battery Amp-hour Capacity Tester

Battery Charge Current Indicator

Battery Eliminator

Battery Free LED Flasher

Battery Polarity Reversal protects Circuit

Battery Powered Plus-Minus 15v Supply

Beeper that is Very Loud

Bidirectional DC Current Indicator

Bidirectional Solid State Relay

Broad Band 2Mhz Optical Fiber Receiver

Broken Solar Panels

Brush Motor Speed 12V Controller

Button Battery Cell Internal Resistance Measurement Circuit

Camera Shutter Time Measurement

Candle Power

Capacitance-Type Liquid Level Monitor

Caps Provide Voltage Boost to Series Regulator

Car Ignition 12v Switch

Cascode Light Receiver Circuit

Chain Link Fence Alarm

Charge Coupled Bi-Directional Power MOSFET Relay

Charge Coupled MOSFET Relay #2

Charge Pump Efficiently Divides Supply Voltage 

Charging a 24v Battery Charger from a 12v Source

Cheap Close-Up Camera Lens

Cheap Light Power Meter

Chicken Coop Door Opener with Timer

Circuit Forms Divide By 1.5 Counter

Circuit Forms Ideal Diode Function

Circuit Indicates Battery Charge Current

Circuit indicates Battery Charging Current

Classic Linear 5v Supply using 6.3vAC Transformer

Classic Plus & Minus DC Power Supply

Clear Fluid Detector #2

Clear Fluid Monitor

Click Sound Generator

Closet Light with Automatic 3-Minute Timeout

CMOS Inverter 125khz LC Oscillator

CMOS Inverter Parallel LC Oscillator

CMOS Logic Inverter Amplifier Characteristics

CMOS Nand Gate Forms Gated 125Khz Oscillator

CMOS Schmitt Trigger IC Makes VCO

Coin Operated Telescope

Color Film Makes Optical Filter

Computer Controlled Power Relay

Computer Controlled PWM Circuit

Constant Current LED Driver

Convert Solar Powered Light to Flasher

Corona Monitor

Crystal Controlled 1KHz Signal Generator

Current Indicator for Battery Chargers

Current Injector

Cut Phone Line Alarm

Darkroom Camera Shutter Timer

Day/Night Switch-24vAC Powered

DC Brushless Motor Monitor

DC Current Indicator #4

DC Current Indicator 6

Delayed Pulse Generator

Detect the narrow 1uS pulses

Detects Shadow Activated Motion

Digital Counter using Pedometer

Digital Counter using Pedometer

Do It Yourself Portable Cell Phone Charger

Does Power Line have 120 VAC or 240 VAC?

Doggie Water Dispenser Alarm

Door Knob Alarm

Door Knock Beeper

Drive a LED with an Intensity Ramping Mode

Dusk To Dawn Latching Relay

DVD Recorder + TV Camera Make Cheap Data Logger

Earthquake Alarm Circuit

Earthquake Alarm Circuit

Electric Field Disturbance Monitor-Alarm Discriminator + Battery Monitor

Electric Field Disturbance Monitor-Front End + Power Supply Circuit

Electrical Current Indicator

Electrical Device Harvests Earthworms

Electrodeless Water Level Monitor

Energy Harvesting using a Current Transformer

Expanded Scale 12v Battery Voltage Monitor

Fake Car Alarm Light

Fake TV Camera Flasher

FET Input High Speed Light Detector

Finger Tap Piezo Relay

Finger Touch Activated Switch

Flashing LED Power Indicator

Freeze Alarm

Freezer Over-Temperature Alarm

Freezing Temperature Alarm

Full Wave Rectifier

Garage Door Timer

Generate 0.5v Negative Supply

Hand Wave Motion Detector

High Ambient Light Immunity Light Detector

High DC Current Indicator

High Intensity Line Powered LED Flasher

High Pass Active Filters

High Power LED Flasher

High Power Touch Switch Exciter Circuit

High Sound Output Beeper

High-speed 75MHz light receiver

HO Train Lighthouse Flasher Revisited

Homemade Corner Cube Reflector

Honeybee Counter

Human Footstep Alarm

Human Traffic Footstep Detector Preamp

Illuminated 16vAC Doorbell Lamp Replacement  

Improved Solar LED Spot Light

Improved Solar Path Light

Incandescent Lamp Inrush Current Limiter

Indicates when it is Time to Dust

Indicates when it is Time to Dust

Inductor Self-Resonance Tester

Infrared Reflected Light Switch

Infrared Safety Switch

Infrared TV/VCR Remote Booster

Insolation Solar Monitor

IR Remote LED Indicator Light

Isolated AC Current Monitor

Isolated AC Voltage Spans 0VAC to 280Vac

Isolated Power Supply for Digital Panel Meters

Isolated Remote Switch Circuit

JFET High Impedance Buffers

Knocking rings Doorbell

Laser Diode Tester

Laser Used as Vehicular Traffic Counter

Laser/LED Light Output Intensity Meter

Lead-Acid Battery Low Voltage Indicator

LED Camping Lantern with Dimmer

LED Driver using Constant Current

LED Driver-Wireless

LED Pilot Light powered by AC Line

LED Strings powered by AC Line

Light Detectors with Ambient Light Compensation

Light Intensity Monitor

Light Intensity Monitor

Light to Frequency Converter

Light/Dark 12V Switch

Lighthouse LED Flasher

Line Powered 60hz Clock Generator

Line Powered High Intensity LED Flasher

Line Powered White LED Array

Line Status Indicator for 1 Telephone Line

Line-Powered Xenon Flash Transmitter

Lithium Battery Tester

Lithium Ion Solar Battery Charger-#2

Logic Controlled 12v DC Motor with Automatic Brake

Long Period Computer Watch Dog Timer

Low Frequency Oscillator draws only 2 Nanoamps

Low Power 100khz Light Receiver

Low Power AC to DC Power Supply

Low Power Amp Monitors Light

Low Power H Bridge Motor Controller

Low Power Universal LED Flasher

Low Value Capacitance Meter

Low Voltage H-Bridge

Low Voltage Latch Circuit

Low Voltage Latching Relay Driver

Low-power optical interrupter

Machine Power Loss Beeper

Machine Vibration Triggers Hour Meter

Make a Geophone to Detect Foot Steps

Medium Power 125khz Oscillator

Medium Power 125khz Oscillator #2

Medium Power 40Khz Ultrasound Transducer Driver

Micro Power 40Khz Burst Laser Diode Driver

Micro Power Over-Temperature Alarm

Micropower CMOS Oscillator, Draws Only 0.5ua

Miniature 24VAC Isolated +5V Supply

Miniature 5v Line Powered Isolated Supply

Miniature Isolated AC/DC Power Supply

Miniature Lighthouse Light Simulator

Miniature Pushbutton On/Off Switch

Mm5437 Noise Generator

Model Airplane Wing Tip Flasher

Modified 4 D Cell LED Lantern

Modified Cheap Solar LED Path Light

Modified Colman Lantern3

Modified LED Night Light

Modified Shake to Charge Flashlight

Modulated Light Monitor #1

Modulated light receiver circuit

Monitor Clear Fluids

Monitor Water Seepage

Monitor Water Seepage

Monitors Pump Motor

Motorized Duck Decoy Timer

Moving AIR Indicator

N-Ch & P-Ch Transistor Form Push-Pull Driver

Night Light from White LED

Non-Isolated Off-Line AC to DC Power Supply

Non-Isolated Off-Line AC to DC Power Supply

NPN/PNP Transistor Tester

Ocean Wave Power Generator Demo Unit

On/Off Flip/Flop Circuit with Automatic Timeout

On/Off Latch Circuit

On/Off Latch Circuit with 2 Second Delay

On/off Pushbutton Switch with 30 Minute Timeout

On/Off Switch with Latching Relay

One Shot (D-Flip/Flop) Circuit

Optical RFID Test Circuit

Photo Transistor interface Circuit

Piezoelectric Tap Switch

Piezoelectric Triggered Switch

Piezoelectric Vibration Sensor Activates Switch

Plastic Pipe Finder

Poor Man's Timer

Poor Man's Timer

Pop Free Microphone On/Off Switch Circuit

Pot Controlled Variable LED Intensity Circuit

Power Reminder Beeper

Power Supply-24 Volts AC to 24 Volts DC

Precision 40Khz Triangle Generator

Precision AC Peak Detector

Precision Fullwave Rectifier

Pulse Period to Voltage Converter

Pulsed LED Test Circuit

Pushbutton Activates Service Request Beeper

Pushbutton Controlled Up/Down Ramping Light

Pushbutton Oneshot & Latch

Pushbutton On-Off Latch Circuit

Pushbutton Switch works through Glass

PWM Circuit for Motor Speed Control

Radio Tower Lamp Monitor

Ramping Lamp Driver

Ramping LED Driver

Rapidly Stops DC Motor Drive

Reduce voltage to Photovoltaic Solar Panel with Ideal Diode

Reduced Power Relay Driver

Reduced Power Sequential LED Flasher

Remote Doorbell Beeper

Remote Range Extender TV/VCR

Remote Relay Driver

Remote TV Camera Power

RS232 Data Bus Status Monitor

Safety Light

Scare Off Pigeons

Self-Powered AC Current Indicator

Servo Pulse to Voltage Converter

Servo Pulse to Voltage Converter

Simple Circuit for White LED Night Light

Simple Circuit Nitrogen Spark Generator

Simple Circuit Wire Security Loop Alarm

Sink to Source Universal DC Converter

Small Battery Capacity Tester

Small Pushbutton Controls 10 Amps AC

Snow Depth Alarm

Solar Cell Test Fixture

Solar Fireflies In Jar Light

Solar Insolation Monitor

Solar Insolution Meter

Solar Lithium Ion Battery Charger using LT1129

Solar Mason Jar Light

Solar Path Light Improvement

Solar Path Light Improvement

Solar Powered Cell Phone Charger

Solar Powered Flood Light using NiMH

Solar Powered Infrared 1W Security Camera Illuminator

Solar Powered Lighthouse

Solar Powered Lithium Ion Battery Charger

Solar Powered Lithium Ion Battery Charger

Solar Powered Quartz Clock

Solar PV Cell Test Fixture

Solar-Powered Pump Motor Controller

Solid State Relay Requires Only 50ua Drive Current

Solid State Relay that is Bidirectional

Sound Triggered Night Light

Square Wave Driver Has Flexible Outputs

Star Trek Doorbell

Super Bright 3v Powered LED Flasher

Supercapacitor Voltage Limiting Circuit

Table Lamp with Auxiliary 12v Automotive Style LED Light

Temperature Sensor MOSFET

Temperature Sensor with 4 to 20ma Current Loop

Tester for Modulated Light

Thermocouple Temperature Activates Relay

Tool Shed LED Light

Triangle Signal Generator

Two Pushbutton Motor Controller

Ultra Low Current 3v LED Flasher #3

Ultra Low Current Oscillator

Ultra Low Current Oscillator #4

Ultra Low Power Astable Multivibrator

Ultra Low Power Human Finger Detector

Ultra Low Power Latching Relay Circuit

Ultra Low Power LED Flasher

Ultra Pure 125kHz Sine Wave Signal Source

Under/Over Voltage Alarm on AC Line

Universal Flasher using a Latching Relay


Unplugged Appliance Alarm

Unplugged Power Cord Alarm

Version a of 1.5v LED Flasher

Vertical Lifting Security Gate Power Source

Very Loud Pulsating Beeper

Very Low Power Astable Multivibrator

Very Low Power Gated Crystal Oscillator

Very Low Voltage Oscillator Circuit

Video Signal Edge Enhancements

Voltage Boost

Voltage Converters-0.5 to 6 Volts

Voltage Limiting with a Supercapacitor

Voltage to Frequency Converter + 1us LED Pulse Driver

Water Cistern Level Alarm

Water Filling Station Controller

Water Flowing in Pipe Indicator

Water Seepage Monitor

Watt-Hour Meter Monitor

Wave Power Generator Demo System

Well Pump Flasher & Beeper

White LED is Powered By One NiMH

White LEDs powered by 24V

Wide Band Zero Cross Detector

Wig/Wag LED Flasher

Wireless LED Flasher

X100 Scope Probe

Xenon Lamp Flash Detector Amplifier

Hobby Circuits List

Suggested Electronics Tool Kit List

eMail:  David A. Johnson, P.E. about these circuits



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