Circuits designed by David Johnson, P.E.
Last Updated on: Friday, December 29, 2017 02:53 AM


Text & Graphics Copyright © David A. Johnson, PE  --  ALL Rights Reserved.
LINKING to Dave's circuits is permitted but COPYING CONTENT to your WEB SITE server IS NOT!

Check Engine Beeper

Chicken Coop Door Opener with Timer

Classic Plus & Minus DC Power Supply

Clear Fluid Detector #2

Current Indicator for Battery Chargers

DC Current Indicator #4

DC Current Indicator 6

Does Power Line have 120 VAC or 240 VAC?

Either indicates 120 VAC or 240 VAC

Electrical Current Indicator

Fake Car Alarm Light

Flashing LED Power Indicator

Four Line Telephone Line Status Indicator

High Intensity Line Powered LED Flasher

IR Remote LED Indicator Light

Lead-Acid Battery Low Voltage Indicator

Low Battery Voltage Flasher

One-Line Telephone Line Status Indicator

Optical Fiber Indicator

Remote LED Indicator Light

RS232 Data Bus Status Monitor

Self-Powered AC Current Indicator

Serial Data Bus Status Monitor

Two Transistor Oscillators

Version a of 1.5v LED Flasher

Water Flowing in Pipe Indicator

Wave Length Indicator

Wireless LED Flasher

1 Line Telephone Line Status Indicator 

1.5v LED Flasher Version A

125khz Wireless Smart Key Detector

12v Lamp Current Indicator

12v Touch Switch Exciter Circuit

1uS Light Pulse Receiver + Post Amp

2 Line Telephone Line Status Indicator

2 Transistor Oscillators

3 Volt Low Battery Voltage Flasher

36-Hour Watchdog Timer

4 Line Telephone Line Status Indicator

Acceptable Voltage Indictor

Active AC Power Line Indicator

Alarm Beeps when the “Check Engine” Light Turns On

Alkaline Low Battery Voltage Indicator

Automotive Electrical Voltage Indicator

Bad Light Bulb Indicator

Battery Charge Current Indicator