Greetings from Canada!
Wow! All this time, I thought I was working on a uC - dew point based Dew Controller without any one else doing the same. I have chosen and aquired the Relative Humidity sensor (a Humirel HS1101) and temperature sensors (LM135s) and am now at the point of chosing a uC. This is where I hit a wall.
Do I choose a uC that can do the math (dew point calculations using relative humidity and ambient temperature requires logarithmic functions, especially at less than 50% RH), do I choose one that can do the A2D for the temperature sensors or do I choose one that can do the PWM for the O/P? The alternative is to choose one that can do it all - which is not really a problem (except for the math), if you are making a single O/P controller. I plan on making a 4x O/P controller (Dob primary, secondary, eyepiece and finder). I have now discovered
http://www.awce.com/index.htm. They supply coprocessors for use with AVRs, PICs or any othe uC and have scaled my uP back to a simple I/O pin choice leaving the math and A2D up to the PAK-IX (combines ALU and 5x 10-bit A/D channels) and the PWM to the PAK-V (8 simultaneous PWM outputs). They do seem a bit expensive, however I am willing to pay more to simplify the design. The PWMs will need power switchs on the O/P - likely FETs.
The "stand alone" operation will raise the optics to a couple of degrees above the dew point temperature (or frost point temperature - which can be below the ambient air temperature below freezing) in a effort to preserve batteries and make the heating efficient. I believe I can fit the circuit onto a board about 2.5" by 4" in size and plan on mounting it in my power center (tool box with 2x 12v12AH batteries, power supply / charger) which travels with my scopes.
Regards,
Tom