This is a retro-tech implementation of the classic HP-25 calculator. I love the HP-25, and wanted to create a larger-than-life (literally) recreation. Using the original chips is out of the question, so I've chosen to use a Z80, which was introduced at about the same time (1976 vs 1975 for the HP-25). I started with some inspiration from Eric Smith's excellent ​nonpareil simulator and the equally excellent ​reverse-engineering done by Jacques Laporte (R.I.P.).

Events

• ​https://hhuc.us/

HpCalcBuildLog

Hardware

• Github: ​https://github.com/eshazen/retro-25
• SVN: ​http://edf.bu.edu/svn/edf/EricHome/HPCalcSim/
• Keyboard/Display: ​SVN ​sch(svn) ​Schematic (preliminary) ​layout ​gerbers (Rev 1)
  • Board with Cherry MX switches in classic HP-25 layout and 10mm 12 digit red LED display driven by two ICM7218A.
• CPU: ​(SVN sch) ​Schematic (preliminary)
  • Z80 10MHz cpu with 32k EEPROM, 32k SRAM and dedicated I/O for the keyboard/display.

• Keyboard
  • Best bet seems to be Cherry MX keyboard switches
  • Keycaps: ​https://pimpmykeyboard.com/dsa-relegendables-pack-of-10/
  • Very Useful: ​https://matt3o.com/book/ (book on custom KB)
  • Custom jobs: ​http://www.wasdkeyboards.
  • ​http://www.keyboard-layout-editor.com
• LED ​LTC-4627JR (10mm common Anode)
  • Driver: ICM7218A (common anode, 8 digit driver). Recommend common anode as no external drivers or resistors are needed.
• Case - Hammond 1456FH3 ?
• CPU
  • Z84C0020PEG (20MHz Z80 or 10MHz if 20MHz not available)
  • AT28C256-15PU (32Kx8 150nS EEPROM)
  • AS7C256B-15PIN (32Kx8 15nS RAM)

References

• ​https://medium.com/@erikvanzijst/diy-eeprom-programmer-4fd11a486ea
• ​https://hackaday.io/project/7306-np25-calculator
• ​https://github.com/simpleavr/NP25
• ​http://ohm.bu.edu/~hazen/Eric/NP25-master.zip (backup of GitHub?)
• ​https://www.hpcalc.org/authors/1105 (Eric Smith, Nonpareil and CSIM downloads)
• ​http://www.teenix.org/ Another PIC based set of emulators
• ​http://home.citycable.ch/pierrefleur/Jacques-Laporte/index-old.html - the famous Jacque Laporte (RIP) site
• ​http://z80.info/z80-op.txt
• ​https://archived.hpcalc.org/laporte/Woodstock/ws_HW_main.htm
• ​http://www.vcalc.net/hp-code.htm