HP-25C Eumulator

[Chris Chung]

(09-25-2014 07:38 AM)Harald Wrote:  Is your software available somewhere? Id love to try and make a board that fits inside a woodstock calculator. I would not try and reuse the original keyboard, as those often suffer from leaking batteries.

I will put the source up on github this weekend. It's not very clean as I am not ready to clean out things that can help me debug. But it works well.

(09-25-2014 12:13 PM)Harald Wrote:  I'll have a look at one of my dead Woodstocks when I get a chance. The idea would be to install a PCB with tactile switches and use the original keys to press the switches.

This would be easier as I found out that the original HP-25 key scanning is done on a 5 x 7 matrix. My design is of 3 x 12 and I don't have extra IO pins to change it to 5 x 7. I.e will have to add a IO expander chip. The PCB layout could be tricky though.

(09-25-2014 01:25 PM)walter b Wrote:  

1. Wouldn't it make sense to think about a 29C emulator (as well or instead). Advantage: subroutines.
2. Since memory isn't the limiting factor anymore, would it be possible to allow that emulator accessing a bit more than the 49 or 98 program steps, respectively, the originals had? May be an addressing issue, however.

Just crossed my mind.

(1)
It can run whatever ROM (woodstock / spice) that nonpareil can run. I.e. 21, 25, 25C, 32E, 33C, 34C, 37E, 38E, 38C. The TI mcu can hold 16K flash. You can fit a 21 + 25C in it at the same time. I can use a "hold button + switch on" kind of scheme to select ROMs at startup. Like this one that have both a TI DataMath and Sinclair Scientific ROMs.

http://youtu.be/9ElT7siDtaE

For the biggest ROM (34C), it can only hold one. Also the TI msp430g2553 has only 512 bytes of RAM. So there is only may be 1/2 the 210 steps? for the 34C.

I only tried 25C and 34C ROM and they both work correctly. Of course the program steps is not full for the 34C. The other ROMs should work by replacing a header file. But I don't see the 29C being supported by nonpareil.

(2)
Yes, for the 25C and other woodstock models, we can lift the limit and make use of extra program steps. Again the MCU I choose has only 1/2K RAM and the program steps need to run off RAM (or at least for now). And the emulation itself requires RAM for stack and stuffs. So there is a limit to this.

* You may ask why I did not choose a powerful chip. Perhaps do it w/ a ARM Cortex, etc. The answer is that I prefer to use lesser devices, simple, very easy to build for this project. The all thru-hole DIP components allows for any average or occasional builders to make this.