Rich user interface shield (f/stop timer)

I've released Rev.B of my f/stop timer, a photographic enlarger timer. While the actual timer functionality is probably of little interest here unless you're an analogue photographer, the shield itself is all about user interface. It provides support for:

  • 4x4 matrix keypad
  • HD44780 with PWM backlight dimming
  • quadrature rotary encoder with push switch
  • frequency/period input (T1, ICP1), e.g. for measuring light using TSL235 or any other freq source
  • simple relay driver (R+BC548+diode) on D13
  • about 3 spare pins (D0/RX, D1/TX, A5) so you can do serial and a shift-reg/IO-expander output
  • bridge+capacitor for 5VAC power input

It's all open hardware+software, full source code and design files are provided at the link above, or you can buy one of my spare PCBs for $10+postage; I had a big batch made to service demand from the analogue photo community on APUG.

If you need lots of outputs then this is not the board for you. If you need a deep user interface and only a couple of output bits, it works pretty well.