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.

Design

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

• Schematic (ExpressSCH) -- ​SCH ​PDF
• PCB Layout (ExpressPCB) -- ​PCB (including JTAG adapter for another project) -- ​PDF
• Parts List (OpenOffice?) -- ​ODS

• HP-35 on Arduino -- ​Jacques Laporte's site -- ​Local Mirror

Parts:

• 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.