Need to design a small disconnect circuit

Sounds like you need a small moisture sensor driving a FET. Moisture sensors usually are looking for (ahem) moisture, but there is no reason one shouldn't work for detecting frost or ice. The sensor is easy to make - two electrical contacts in close proximity but not quite touching. Put a small DC voltage across the contacts, and look for the small current that results when they are bridged by moisture. I'm sure Google will turn up hundreds of sensor designs.

Bill

Kinda like a howitzer for a mosquito.

But you are looking for Thermistor Probes if all you want is a sensor and they are readily available. Just do a search on that and see what you get.

Peter Wieck Wyncote, PA

thanks everyone for ideas. I will look up information. pls if you have any more ideas do let me know.

it

any

There are a number of electronic thermostat kits available but if you would like to roll your own then the schematic on this page (lower portion)

Take a look at this simple solution:

But distinguish between freezing cold and icing up. 32F precedes icing. I'm not sure how you'd go about detecting ice - maybe some photoelectric device (a hunk of ice blocking a path or causing a change in reflectivity.)