Darkroom thermostat - safety with low voltage

2-58 - elektor february 1982 dark room thermostat dark room thermostat safety with low voltage The photographers amongst our readers will agree that one of the most critical points of printing photographs is the correct temperature of the baths. Specifically the paper developer needs a constant temperature, otherwise the photograph will be anything but brilliant. With the often used PE photographic paper it is strongly recommended that the temperature is maintained at 20¬?C. The circuit described in this article takes care of that. It will be obvious that not too much extra energy is required in the developer bath, assuming that the temperature in the dark room doesn"t drop below 16¬?C. This fact offers the possibility to use a heating element having a lower voltage than that of the mains. Such a low voltage element is not only safer, but also very easy to construct with the aid of a length of resistance wire. The circuit The circuit diagram is illustrated in figure 1 and consis...