As technical director at the Bushwick Community Darkroom, I’m always putting out fires. One of my favorite machines of all time is our Kreonite color paper processor. It’s used to develop prints from the color darkroom, and it’s a complicated beast with hundreds of gears, tubes, wires, and rollers. One of its main functions is to keep chemistry at a precise temperature.
The night before I was supposed to teach a class on how to make color darkroom prints, I was working on the machine when I heard a “pop” and saw a small puff of smoke. Some water had gotten into an electrical junction and shorted out the relay that controls it. The relay was stuck in the on position, and the chemistry just kept getting hotter and hotter.
I grabbed my box of Arduino junk, and whipped together a replacement using the parts I had on hand. One liquid temperature probe, a Chinese takeout plastic container, a 10k resistor, some alligator clips and a 220v mechanical relay. I wrote a small script that polls for the current temperature, and switches the relay appropriately to maintain the proper temperature at surprisingly high precision. By 6AM, I was ready to call it a night and declared it a success. My improvised thermostat has been sitting there, built in its little plastic box, for over six months now with no problems. Pretty impressive, but people still get confused by the takeout box with a glowing red light with wires coming out of it.