HP-25C Eumulator

[Jim Horn]

Indeed - one of the main chips in the '20 series has a strong tendency to be destroyed if the calculator is plugged in for battery recharging and the batteries are not in or otherwise good and well connected. My 1975 '25 (non-C) is one such. As such, since the chips are long out of production (and the standard battery charge circuit is so ruinous), replacing the main PCB with a variant of yours would be terrific to get these fine machines working again.

It would be easier too - the keyboard and display are already provided. The battery pack could easily be replaced as well either with primary cells or higher capacity NiMH or lithium using readily available battery maintenance ICs.

When you open-source your design, would you mind if I look into the above? It would certainly be open source as well.

Many thanks for your fine work!