cathode for HP91

[Thomas Radtke]

(07-31-2015 04:04 PM)Katie Wasserman Wrote:  [...] you're stuck with using an SMD chip on a carrier-like board or wiring a 22 conductor ribbon cable in place and locating the circuit elsewhere inside the calculator.

This is what I was thinking of. Programming a serial RAM emulator shouldn't be too hard. Most of the work is soldering the wires. Common anode should also be possible by switching the IOs to input w/o pull up. Problem might be the current. 40mA is probably not enough per digit (all segments plus dot), so it would take a driver. Anyway, piece of cake for our EE-wizards.