Re: Automatic countdown reset timer?

On Wed, 7 Jul 2010 19:33:48 -0700 (PDT), BoyntonStu
<boyntonstu@xxxxxxxxx> wrote:


Sense a person in a room.

Trigger a countdown timer that is preset to a fixed time when a person
is sensed.

(A motion detector or a beam breaker is acceptable)

The timer will control a 110 VAC device that is normally off.

If a different sensor is triggered elsewhere in the house within the
countdown period, reset the timer to the original preset time.


Sounds like you already have a pretty good idea of what you are doing
or want to do.

A single 555 monostable triggered by an inexpensive off-the-shelf
motion detector with an external reset.

But you are probably leaving something out - like what precision do
you want, and does time need to be adjusted with some degree of
accuracy and will it change often, how user-friendly, etc..