darkroom timer with PIC 16F84A

Posted on Jul 11, 2012

I tried to design a timer that would do everything it needed to do but with the smallest number of pieces and simplest mode of operation. It only needs the PIC, a four digit LED display, one other IC, a resistor network, one pushbutton switch and a capacitor. It can run on batteries if you use a solid state relay to turn the exposure light on and off thereby adding a minimum of parts to make a fully functional darkroom timer. A simple regulator would add only a few extra parts and allow the use of a `wall-wart` for power.

darkroom timer with PIC 16F84A
Click here to download the full size of the above Circuit.

All the functions are in firmware, allowing the use of one switch for control. I sketched in the schematic in Eagle format and here's a jpg image, too. This text file has the parts list and some notes to help you build the timer. Here's the firmware. You

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