Darkroom Ratio Calculator

Calculating ratios in my head when mixing/diluting chemicals in the darkroom is hard, so I want to build a box to do it for me.

Project Status

• 2014-12-11: Started building BOM and schematic, put together first ideas for a front panel design.
• 2014-12-08: Started putting together initial idea/design.

Overview

• Input via rotary encoders
• Output on red 7 segment LED displays
• Unit will have a light sensor and dim the displays when the lights are turned off so they're safe
• "Fields" are:
  • Ratio Component A (3 digits) w/ encoder
  • Ratio Component B (3 digits) w/ encoder
  • Value Component A (4 digits)
  • Value Component B (4 digits)
  • Total Value (4 digits) w/ encoder
  • Round To (2 digits) w/ encoder
• Ratio Components, Total Value, and Round To are settable, Value Components are the output
• Round To is a way of automatically adjusting the total to find the nearest value that makes ratio components rounded while staying accurate
  • Measuring 67.2ml of liquid is a pain
• Total required I/O is:
  • 20x 7-segment displays
  • 4x rotary encoder inputs
  • 1x reset button input (resets to 1:1, total 1000, round to nearest 5, or something like that)
  • 1x light sensor input