Timer for PCB Exposure Box

Yet another darkroom timer using a PIC 16F84A. All the functions are in firmware:

  • Lamp(s) light at start of timing and turn off when timer reaches zero.
  • A set of leds were added between the minute and second leds which blink during timer operation.
  • 7 segment displays include tails for digits 6 and 9.
  • A bicolor led (common cathode) indicates standby (green) and timer operation (red).
  • Separate PCBs were designed for the led display and the timing system. The power supply is also integrated in the PCB.

Source: Electronics-Lab


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