cathode for HP91

[Katie Wasserman]

(07-31-2015 08:34 AM)Thomas Radtke Wrote:  

(07-31-2015 08:04 AM)PANAMATIK Wrote:  Although it would need much less work than the new ACT and the concept would be rather easy, the development of a microcontroller based cathode driver is too expensive concerning SMD manufacturing costs for small quantities.

Maybe an Arduino Nano or similar would do. I guess you'd need 14 IOs for the display and keyboard and some control lines (3?).

The problem would be the socket. It's a 22 pin DIP using 18 pins for i/o plus Vcc and ground (2 pins are apparently unused acording to the schematic). I'm pretty certain that no modern microcontroller can match the pin configuration of this custom IC so 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 a possibility in that there's a good about of free space inside a 91/92/97. If you do that you could use almost any micro with enough i/o (and many an ADC for low voltage detection).