Monday, October 26, 2009

On Taps and Positive Feedback

Automatic taps in bathrooms are an interesting idea. Presumably, it’s to prevent the transfer of germs. Each tap has a little motion sensor that detects when something is placed underneath them, and then turns on. When whatever it was is removed, then the tap switches off.

Designing these taps and getting them to work properly must have been a real pain in the neck. They suffer from a serious problem of positive feedback (actually, it reaches a limit where it becomes neutral feedback). Yesterday, I came across one tap that had obviously had its sensor confused. Every time the tap switched off, the sudden change triggered the sensor, which started the tap. But, there was nothing in front of the tap, so it would switch off. It meant the tap was stuck in an infinite loop.

Its a waste of water, but it was amusing to watch.
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