Schematics

The two main elements to this build are: 1. control of the mini-fridge’s peltier element and 2. measurement of the temperature.

Having investigated the mini-fridges internal workings previously, I’ve established that the fridge’s internals is fairly simple, consisting of a large mains to 12V DC supply board, which supplies 12V DC to a switch board. The switch board contains a switche that allow the direction of voltage supplying the peltier to be switched (this allows the fridge to change from heating to cooling modes).

The simplest option in controlling the peltier is to attach a transistor between the mains board and the switch board, this allows the fan to be also switched. I can also splice into the 12V DC rail to power the Forebrain microcontroller board too. Isolating devices are used here (the isolating 12V to 5V DC/DC converter, and an optoisolator fo controlling the transistor.

Oh yeah, I had this LCD lying around too, I’d better throw that in as well:

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