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Circuits designed by David Johnson, P.E.
Last Updated on:
Tuesday, October 24, 2017 03:04 PM
List of Dave's Circuit Designs
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More
Timer Circuits
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Garage Door Timer
May 15, 2011 |
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circuit below is designed to automatically close a garage door, if it was left open
for a long period of time. A reed relay and magnet combination sense when the
door is fully open. |
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An ultra low power voltage comparator oscillator and two 74HC4040 ICs
are used to generate the time delay. A jumper or a switch can be used to
select a time of 30 minutes, one hour or two hours. The circuit draws only
about 2ua so a pair of AA alkaline cells would keep the unit running for many years. |
| Magnet
+ Reed Relay Switch |
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Click
on Drawing Below to view PDF version of Schematic |
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