This is an entertainment/educational project to build a watch which can run the original HP-35 calculator firmware as well as telling time. It has a 34 key keyboard, a back-lit 128x32 graphic LCD and a low power real-time clock. The CPU is an ATMega328, same as in the Arduino. Firmware available at Jacques Laporte's site linked below for HP-35 running on an actual Arduino... shouldn't be hard to port.


SVN (firmware):

3 PCBs ordered 12/17/13 due 12/23/13.


  • NHD-C12832A1Z-FSW-FBW-3V3-ND display
  • ATMEGA328P-A MPU in TQFP-32
  • CFS206-32.768KDZB-UB crystal for RTC
  • MCP79410-I/SN RTC

Alternative switches:

  • CK PTS 810, 820, KMR4 series. 1.5mm body, 1mm plunger
  • EVQ-P2402M etc (Panasonic, DK P11080SCT-ND). *Too Big?* These are 1.6mm body with switch extending above.
Last modified 3 years ago Last modified on Apr 29, 2020, 8:50:07 AM