Talking Darkroom Timer

From Hackstrich

I got tired of having to mess with darkroom timers in the dark while processing colour prints in trays, so designed and built a timer that understands entire processes and walks you through them step-by-step with speech. The timer reads process information from paper instruction sheets using Aztec 2D barcodes and then times each required step.


  • Timer itself, located above the left side of the sink near the ceiling
    • Raspberry Pi 2
    • Adafruit LCD Plate
    • Proto Plate with RS232 level shifter for barcode reader
  • Speaker above the timer
  • 2D barcode reader mounted on the shelf aimed at the wall
  • Control panel below the sink with the following controls:
    • Large green SELECT button
    • Navigation left/right control
    • Active/Standby toggle switch
  • Aztec Code barcodes on each process sheet, which contain all timing information

Usage Procedure

  • Set the Active/Standby switch on the timer control panel to Active
  • Scan the barcode for the process you want under the crosshairs that appear on the wall
    • Barcodes can be found on instruction sheets for each process that are hung up behind the door.
  • Double check that the timer is displaying the process you want to run, and press the big green SELECT button
  • The timer may ask if you want to adjust the time for specific steps.
    • If you don't, just press SELECT.
    • If you do, use the navigation buttons to change to Yes and press SELECT.
  • The timer will show and read out each step as it's ready.
  • Press SELECT to start each step.
    • If you want to run a different step instead, use the navigation buttons to scroll through.
  • To abort a step in progress, hold the SELECT button until you hear a buzzer.

Other Information