There you go! My first desk calculator conversion is complete!

I
bought an Olivetti Logos 262 PD from 1980's, whose only guilt was to
have a VFD display. I reverse-engineered the keyboard connection and
designed a circuit to emulate keypresses with a microcontroller. Once
the circuit has been built and tested, I wrote an Arduino firmware that
reads an RTC (battery-backed clock) and types the numbers into the
calculator. Last but not least, the clock circuitry can be disabled and
the calculator used as originally intended.
Display modes are
bonded to the way a calculator interacts with humans. Mode is changed
towards the end of every full minute and includes:
- YYYYMMDD.HHMM
- HHMM.DDMMYYYY
- HHMM
- DDMMYYYY.HHMM
- HHMMSS
- HHMMSS.DDMMYY
The latter two modes are
interactive in a way that the displayed information changes every second.
One more thing needs to be implemented, both in hardware and software: a way to set time and date!
If you need inspiration, the firmware is on
github. While I have lots of notes on scrap paper, I do not have a complete schematic diagram to share. If I locate another calculator to convert I will draw a diagram so that it can be reproduced.