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Hobby Circuits designed by Dave Johnson

Last Updated on: Tuesday, June 01, 2021 03:22 PM

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!

Indicator Circuits
Circuits designed by David Johnson, P.E. :

Indicates 120 VAC or 240 VAC

Indicates Automotive Electrical Voltage

Indicates Battery Charge Current

Indicates Battery Charging Current

Indicator for Acceptable Voltage

Indicator for Bad Light Bulb


LED Flasher needs only 1.5 VOLTS

Line Powered High Intensity LED Flasher

Line Status Indicator for 1 Telephone Line

Low Current Flashing LED Power Indicator

Low Power LED Flasher

Low Voltage Indicator for Lead-Acid Battery

Moving AIR Indicator

Piezoelectric Water Flowing Indicator

Ramping Lamp Driver

RFID Smart Key Detector

RS-232 Serial Interface Status Indicator Circuit

Telephone Status Indicator for 4 Lines

Three-Volt Low Battery Voltage Flasher

Transmit to a Remote LED Indictor Light

Two Line Telephone Line Status Indicator

Two-Transistor Low Power Oscillators

Ultra Low Power Detects Clear Fluid

Version 4 of a DC Current Indicator

Wireless RFID Smart Key Detector

120 VAC / 240 VAC Indicator

AC Current Indicator Light

AC Indicator-Self Powered

Beeper indicates Check Engine

Bidirectional DC Current Indicator

Call-for-Service Beeper

Check Engine Beeper

Circuit Indicates Battery Charge Current

Circuit Monitors 12v Lamp Current


DC Current Bidirectional Indicator

Detects Xenon Lamp Flash

Flashing Light to simulate Car Alarm

Front Desk Service Beeper

High DC Current Indicator

Hot AC Power Line Indicator

Indicate DC Current Flow

Hobby Circuits by Category

Dave's Circuits

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Copyright  January, 1998 - June, 2021     David A. Johnson  All Rights reserved. 
 Linking is ALLOWED but COPYING any content or graphics to your web site is EXPRESSLY PROHIBITED.