Refrigerator door timer

18-06-2024

As my current refrigerator was much too simple to have a built-in "door open" chime, I've decided to build one, as the market for "aftermarket refrigerator door chimes" is effectively non-existent.

One quick, easy, sane solution would be to use microcontrollers, but between using crystals/op-amp function generators and clock dividers, and going for more expensive microcontrollers (well, not like you can find ATTinies for cheap now), I've done what I could with what I assume most people (including me) have: a 555 and basic discrete components.

The end result was a quick, dirty solution stemming from an astable circuit:

There is a small "glitch" (or feature), where a quick beep is emitted once the door is opened, but I don't mind this too much. You can adjust the warning timer by altering the capacitance (the parallel capacitors don't really matter, I only had 100uF ones). You can calculate the values with this handy calculator!