Jinx wrote...
 >The PIR circuit is stable, no problems in the 6 weeks it's been on so far,
> but if I could make it self-settling that would be a big advantage when it comes
> to installing a number of them. ie set and forget, no need to worry
> about any drift, if it happens. Putting a smaller preset between two
> resistors does make it easier to set, but it does still need to be set
> manually.
>

At a quick glance I would say the answer would be to remove the
10M pot and feed the non inverting input through a low pass of the
inverting input. The low pass being of a value such as to enable
detection over drift.
If the input rises fast enough.... the inverting terminal voltage rises
but the non inverting isnt there yet.... trigger!

I remember doing this sometime in my distant past.
_____________________________

Lance Allen
Technical Officer
Uni of Auckland
Psych Dept
New Zealand

www.psych.auckland.ac.nz

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