Edit: amended some sections
CMOS Heater - aka "defogger"
I have added as much information as is necessary, hopefully, with some order to it. None of this is set in concrete and there is always room for individuality. The idea has been to set out the basics and at the same time present a working model. I hope it's useful.
The code works well and no doubt can be improved by better programmers than me. It's a low level approach. Pretty much where my programming skills sit at the moment.
The setup was tested at the March 2014 Snake Valley Astro Camp, and it ran nicely at -5C for several hours, between 20 and 15 degrees differential. I will post the image when it is processed.
There are some minor improvements and adjustments to be made. If you don't like the analog sensor readings in the program as control points, just convert and use degrees Celcius.
I did notice, on the second night, while focussing with a mask, what appeared to be diffraction due to a small amount of condensation on the sensor face. This did not reappear once evaporated by the sensor defogger. I suspect that the defogger had not caught up with the cooling, due to low air temperature.
Camera has a full spectrum mod with an Astronomik clip-in UV/IR filter from BINTEL. Probably the easiest and less costly option for hobbyists - allows IR as well, with a filter.