The circuit in Figure 1 is a simpler and safer device than a similar one I recently read about (Reference 1). A few years ago, I built the circuit that this Design Idea describes, and the gadget still ...
It beeps if the fridge door is left open for too long or hasn’t closed properly, to stop food from spoiling. There are lots of other uses as well. A refrigerator or freezer door that is left open or ...
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