Hi ppapadeas,
Great idea!
I had a similar idea, as follows:
A board with a microcontroller (Teensy 3.2) controlling two (at least) heaters and a motor focuser. Also on the board a LM2596 power converter to power the Pi and the microcontroller.
It measures the temperature right below the heaters (at the telescope) with thermistors so as to have an actual regulator. I intend to use a HDC1080 to measure ambient temperature and humidity.
I see two dew-controller modes: temperature tracking (with a few degrees offset to correct for discrepancies) or dew point tracking (again, with an offset).
For the focus motor, I think using the TMC2130 is great because the current can be regulated by SPI (forget about trimpots) and the possibility to use 'stallguard' as a sensorless homing feature. Then the focuser can start at the point it was used at the last time.
I would use the Teensy because it can have it's own firmware, and possibly also operate in a stand-alone fashion, using a cheap (or expensive, if that's your flavour) IR remote control for the focus and the heater controller.
Currently I have stripped the 'MyFocuserPro2' firmware and installed it on the teensy. It does communicate and everything so... great!
Only thing is, I've tried connect it directly to the UART of the Rpi 4 (enabling serial in raspi-config) but unfortunately it doesn't connect. Using a TTL-USB converter I can connect it.
A nice add-on would be to incorporate a RTC, or even use a GPS.
Cheers,
Bart
Edit: I've added a photo of what I'm working on at the moment.
Rpi4 connects with the mount via bluetooth. Only one cable goes to the telescope: 12V power.
And working on making a battery-pack counterweight.