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| Planning to build this to notify the kids they’ve left the door open (again). |
From Time Delayed Door Alarm on Homebrew Technology, a blog by Chris Handwerker [KB1WKI]
My cat likes to open the front door if we don’t latch it properly, which is often. Waking up to a cold house sucks! I designed a time delayed alarm with a couple of 555 timers, if the door is open for roughly 30 seconds it sounds off a piezoelectric speaker until the door is closed again.
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