Re: ATM CCD overheat detect/shutdown circuit

["Peter D. Brooks" <pdbrooks@pacbell.net>]

Dominic-Luc Webb molmed wrote:
 The reason: the fan that also
> serves as the pump for the cooling system stopped
> pumping coolant and the chip and other parts burned up...
> 
> :(
> 
> I never actually considered this problem seriously,
> but I guess the cookbook camera is subject to this
> as well. I personally consider this rather poor


>From my reading of the Cookbook and the relevant data sheets, the CCD itself
would be fine at room temp, but if the coolant pump failed, the Peltier device
would most likely overheat.  I believe that the solder that holds the Peltier
together would melt.  Not sure if it would take the CCD with it, but I'd be
wary....

To the best of my knowledge, there is no interlock for coolant flow, but it
shouldn't be too much trouble to implement.  I'd consider a thermometer chip
imbedded in the heat exchanger.  The simple approach would be to have the trip
point set slightly above ambient, with the interlock preventing the Peltier
from being powered up.  This might need an adjustment in case you are observing
in a really hot climate.

There's a National Semi part that acts as a diode with a forward voltage =
10mV/degree K.  Tie one or more comparators to the output and you can a simple
interlock that can handle multiple options (warning light/buzzer, Peltier
interlock, CCD powerdown, et cetera).  Not sure of the part number, though.

Pete Brooks