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

Detects Low Voltage 120VAC Power Line

Doorbell heard in Basement

Earthquake Alarm Circuit


Flashing Light to simulate Car Alarm

Footstep Alarm for Human Traffic

Front End + Power Supply Circuits of the Electric Filed Disturbance Monitor

Indicator for Bad Light Bulb

It's Time to Dust Indicator

Knocking rings Doorbell

Next-Generation Star-Trek Doorbell

Over-Temperature Micro-Power Alarm

Piezoelectric Device used for Motion Alarm


Shadow Activated Motion Detector

Snow Depth Alarm

Still Another Very Loud piezo Alarm Beeper

Sweeping Siren Alarm-3 volts

Time to Dust

Touch Alarm for Door Knob

Water Seepage Alarm

Wire Loop Security Alarm

AC Line Under/Over Voltage Alarm

Alarm Discriminator + Battery Monitor of the Electric Field Disturbance Monitor

Alarm for a Chain Link Fence

Alarm Sounds At Freezing Temperatures

Alarm Sounds when Phone Line is Cut

Alarm sounds when Power Cord is Unplugged

Appliance Unplugged Alarm

Basement Remote Doorbell

Battery-Powered Freezer Alarm


Circuit Monitors Power Loss

Clip-on AC Current Indicator Circuit

Detect Motion with a Piezo Device

Detector for Human Footstep


Hobby Circuits by Category

Dave's Circuits

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