Re: [ATM] Electronics help needed - temperature control

[Mark Holm <mdholm@telerama.com>]

Actually, it is Don Clement's circuit at www.atmsite.org

I think the differential temperature aspect of Don's circuit should be
kept intact.  What all the mirror fan guru's preach is that it is
temperature difference that counts and, quite importantly, that
temperature steadily drops during a typical observing run.  A fan wired
to control at a fixed temperature would have to be adjusted all night
long.  Don's differential circuit would keep up with the temperature
changes automatically.

So Don, how about mods to run a fan off of the differential circuit?

Unlike a heater, there is probably some minimum voltage that you
wouldn't want to drop below.  I am guessing that fans stop turning below
a minimum that is significantly above zero.  It would just be a waste of
power to leave the current on below that voltage.  Probably have to have
a pot on that one, because different fans probably respond differently.

Really, one might want a V shaped response curve.  One leg for cooling
temperature vs. time and the other leg for warming, just in case.  That
is, unless the mirror is equipped with the dew heater.  OK, the V shaped
response is probably gilding the lily.  It might be useful for a few,
but probably not for most.

Mark Holm
mdholm@telerama.com

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