On Tue, 28 Jan 2003, William Chops Westfield wrote:

*>While we're on the subject:
*>
*>Assorted products turn on with the touch of a momentary switch, and turn
*>off either by more button pressing, or by timer.
*>
*>Do these work simply by using the sleep mode of a microcontroller, or do
*>they use some kind of cpu-controlled switch?  I'm thinking LED keychains
*>and such here, and it seems that battery life is longer than I'd expect
*>even for a micro in sleep mode, given the small batteries!

There are chips for that but most cheap products use a transistor circuit.
The button charges a capacitor and when it discharges the light goes off.
Depending on how much you pay the turnoff can be gradual or abrupt.

Peter

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