I'm calling this complete. There are some cosmetic fixes intertwined with sealing the camera, as a whole. Not sure how big this task will be, as it involves making an airtight cover molded to the camera yet providing access to all controls. For the time being the electric sensor defogger is doing its job.
The features of the system are as follows;
- Tidy integrated installation
- Thermoelectric cooling control
- Camera power - no batteries
- Switchable dew heat controllers x2
- OLED display of all the necessary and nice to watch parameters
- Cooling differential 27.5C below air temperature.
On the control side of things
- Automatic preset of cooling set points (10, 5, 0, -5C and -10 with Argon - must seal the camera)
- Manual setting of set point (15C to maximum differential)
- Dew heater manual ON/OFF
- Dew heater auto protection (if desired)
On the setting side of things (EEPROM for the Arduino officiando's)
- Programmable maximum differential (cooling control based on this value)
- Programmable temperature control fine tuning
- Programmable temperature sensor calibration
- Temperature sensor supply voltage continually updated to improve sensor accuracy
Redundancy
- Dew heater output can be adapted for cooling in the event of cooling component failure.
- LED indicating of set point and home temperature settings - just in case the OLED fails.
- Auto requires no indicating at all - but it's nice to see the internal LED illuminated at set point temperature
I've made some changes to the circuit to better manage the current demands of the TEC to avoid overheating the 12V traces - this is a design fault and will be fixed in the new version of the board.
The circuit is mixed signal and very quiet. I see no evidence of interference with the camera, even with 2x pwm outputs driving the heaters at different rates.
As mentioned cooling control is modified and very stable. A little slower to cool down to set point, but steady as a rock when it gets there.
Interesting and educational exercise. Photos to follow, once the sealing is complete.
EDIT: Metro timer came to the rescue to schedule the pulses to the TEC - no delay(); - just like blinking an LED.