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DiscoverCircuits.com -- Hobby Corner
Last Updated on:
Wednesday, June 02, 2021 04:45 AM
Hobby Circuits List
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LINK to Dave's circuit, but DO NOT COPY any files to your WEB
SITE server |
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More Alarms,
Indicators, LED Circuits |
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Time to Dust Indicator
(May 7, 2006)
designed
by David A. Johnson, P.E. |
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I have used the circuit below for many different applications, which require
ultra low power drain. It uses a single CA4013 flip/flop. One section forms a
pulse generator. The generator produces 100uS pulses at a rate of about 1 per second.
The pulse drives an infrared LED. Light from that LED spills out onto a flat surface.
A matching phototransistor, positioned at a 90-degree angle from the LED monitors the light
reflected off the dust particles on the center surface as the drawing below depicts. |
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A circular plastic shield prevents most ambient light from reaching the phototransistor. The
second flip/flop within the CA4013 package, changes state whenever there is sufficient light reflected off the
dust in the middle of the sensing device. When the flip/flop changes state, it drives an n-channel FET, which can be used to turn on a flashing light.
After the other surfaces have been cleaned, a quick wipe with a dust cloth will prepare the
device for another monitoring cycle. The average current drain from a 3v lithium cell
battery is about 5 microamps, so one battery should power the circuit for many years. |
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Click
on Drawing Below to view PDF version of Schematic |
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