[rcheshire (Rowland)]

Nope! Wired the pushbutton incorrectly and shorted the whole thing? All working now... attached below.

Small change - low side switching the dew heater only. As this rig will image at 0C, over a wide range of ambient temperatures sensor deffoging is on while cooling is operating

The dew heater is low side switched through an N-channel MOSFET below 5C for now. Easy enough to use a humidity module as a reference.

There's not much more to this and it's time to start imaging with it.

Summarizing this rather drawn out escaped. Thermoelectric cooling of a DSLR sensor is not too difficult, providing the camera is easily adapted. Regulating setpoint temperature has several advantages, such as consistent and reliable image calibration results. Control using PWM and a MOSFET to switch current through the TEC module presents one or two challenges. Switching of the MOSFET shows up as lines in images, if EMI is not reduced to insignificant levels. Ground planes and careful separation of analog and digital ground sources and camera chassis and cold finger bonding has produced best results.

I will post the Eagle .brd file, although it hasn't changed much, along with the cold finger dimensions. There is a link to the heatsink in an earlier post to this thread - heatsink performance is critical. Cooling performance is related to heatsink and fan performance, TEC rating and supply voltage - if the heatsink/fan cannot keep up the TEC will expend energy heating the system - indiscrimately.

Test the system at various PWM settings note the max differential and PWM setting. If the best differential is at a PWM value less than 100% then the heatsink is probably too small or the fan is not moving enough air or both.

The system will shut down automatically on the predicted failure of certain components - that is; anything that is getting outside desired temperature levels.

EDIT: Uploaded edited circuit diagram - added the latest PCB version..