1100D Set-Point Cooling with Peltier TEC and Air Cooling - v3

[Gina]

Peltier coolers don't take kindly to being temperature cycled so the traditional thermostat is unsatisfactory as it would result in a shortened life for the Peltier TEC. This is why I adopted pulse width modulation at a few hundred Hertz (cycles per second). Analogue variable voltage control would waste a lot of power and generate heat so the switch-mode PWM method was used.

The principle used for fixed temperature is that the cold finger (and hence approximate sensor) temperature is measured with a digital thermometer and fed to the Arduino. Then the effective power fed to the Peltier Tec is adjusted to attain and maintain a certain cold finger temperature.

I also added another control mode whereby the cold finger temperature was set to one or two degrees C above the dew point thereby avoiding condensation regardless of the amount of moisture in the air around the sensor. To do this the relative humidity and temperature of the air immediately adjacent to the sensor is measured and fed back to the Arduino. From these measurements the dew point (temperature at which dew will form on a surface) is calculated. The cold finger temperature can then be set a little higher to prevent dew forming on the sensor cover glass (or filter if fitted). The display shows the dew point and cold finger temperatures plus the RH and set point temperature (the temperature set up in the menu).

I realise that this is rather technical and some modes could be omitted. OTOH if the Arduino sketch and electronic construction were to be copied from my plans, you should be alright. The new version without local display and menu buttons will be a lot simpler to construct as these functions will be carried out by software rather than hardware. BUT I haven't written the PC side of the software as yet.

[Gina]

I don't expect to be adding anything further to this thread as the development has taken a different direction - removing the Colour Filter Array (Bayer mask) from the sensor, converting it from a one shot colour to a monochrome camera. As a result I shall want to reduce the optical path to anable a filter wheel to be used. In view of this I have started a new thread - http://stargazerslounge.com/topic/192357-debayered-and-cooled-1100d/ and will be continuing there.