My “shack power supply”, a Palstar SPS8250, is providing me with 13.8V at up to about 25A for various pieces of radio equipment. It is mostly running with a very low load, 1-2A, and don’t really need the active cooling of a fan. Since the fan is a bit noisy, I made a simple thermostat so that the fan could stay mostly off and only go to full speed at high load and temperature. It is really simple, with an AVR and a few bits of C code to read an LM335A temperature sensor through the ADC and then simply switch the fan through a FET. Two potentiometers are also read through the ADCs to supply high and a low thresholds for the hysteresis. In the picture above, you can see the crude veroboard bolted to the fan in the back of the power supply. The two trimmers are at the bottom, just behind three Berg pins; one connected to ground and the other two to the wipers. This way the thresholds can be read simply by a voltmeter and some basic arithmetic (0-5V = 0-100°C). The LM335A can be seen wrapped in heat-shrink tubing and glued to the heat sink. Except for that I run the whole thing off a supplied fan connector on the main PCB, which apparently has some kind of built-in speed limiting for the fan, it works fairly well. I have it set with about 50°C and 35°C as the high and low thresholds. See full source code at github: avr-thermostat and my ugly schematics/working notes below.
- Take one nice and wide elastic band and pull the ends through the venting holes on a Peltor G22 hard hat.
- From the inside, adjust the size of the elastic loop to fit the player and tie the ends together with a wire tie.
- If you want, add some friction between the player and hat surface by attaching a big furniture feet pad. I used a felt pad, rubber would be better.