The TI 8x calculators are z80 based indeed. The TI 92 and Voyage 200 are Motorola 68K based and very capable in their own right (10-12 MHz clock, lots of RAM, etc.). There are also very good emulators and C compilers for them. (I picked up a cheap TI Inspire to play with, it is awful, terrible KB and poor viewing angle on the LCD)

Several months ago I got an I2C driver working on the V200 (in C) and then ported it to the C64 (in C using CC65). There is a short video here: https://youtu.be/hvPG87acwt4 . I started re-writing it in assembly for the C64 to reacquaint myself with 6502 machine code and got as far as running some simple tests on the various subroutines in debugger in CBM Prg Studio http://www.ajordison.co.uk/ . I thought about getting more familiar with VICE and using one of the built in device emulators as a base to emulate the I2C chip I was talking too but that is more than I wanted to do at the time. It might be interesting to do the I2C driver in Forth to see how it compares to the C version.

I think if I were to build such a 'retro' pocket computer I would want to do the 'old fashioned' 1x24 or 2x20 type LCD dot matrix display. I like the landscape form factor as well as opposed to the typical portrait orientation of a calculator. I have a machine shop at my disposal so the mechanical bits are not a big issue.

I have some 65c02 assembly and Forth source code at http://wilsonminesco.com/6502primer/GENRLI2C.ASM for bit-banging I²C. It goes with the circuit diagram for interfacing to I²C with a 65c22 in the circuit potpourri page of the 6502 primer, at http://wilsonminesco.com/6502primer/pot ... ITBANG_I2C .


There's a lot to be said for those LCDs. They commonly come up to 40x4 characters. I've seen 80x2, but not recently. I do wish they came with smaller characters though. Note that you can make custom characters with them. I have sample code for interfacing to these common LCDs through a 65c22 at http://wilsonminesco.com/6502primer/LCDcode.asm .

I like the landscape factor too, like the HP-75 and HP-71 pictures I put on the first page of this topic. The smaller 71's keyboard is only about 60% of full size, yet I could type on it at about 30wpm (slightly over half of my speed on a full-size keyboard).

_________________
http://WilsonMinesCo.com/ lots of 6502 resources
The "second front page" is http://wilsonminesco.com/links.html .
What's an additional VIA among friends, anyhow?

Well, for these kind of projects, displays are rarely the real issue. It's keyboards. They're neigh impossible to craft yourself, so the next step is to find one you can lift from something and use that instead.

HP keyboards are renowned for their quality and longevity, but most of the HP calcs have a collectible factor to them. Meanwhile, many modern calculators are dirt cheap even if you just salvage them for raw parts.

I agree the keyboard is a problem. I've wondered if a chording keyboard might be a solution. Harder to use, but fewer switches, so it might be hand crafted.

Short of getting your own double-shot keys made, or getting your own rubber keypad made, one sort-of nice possibility is the Grayhill 87 series of keyswitches. They're half inch square each, and come in sets of one to six switches per strip, are side-to-side and end-to-end stackable, have clear snap-in tops that you can put your own labels underneath, and you can hand-mill a square or rectangular hole in an ABS plastic case to fit them perfectly and flush with the top of the case. These have become rather expensive over the last 20+ years, but if you're only making one hand-held computer (calculator form, not touch-tying QWERTY-keyboard form) and count all the time you're putting into it, the cost of the one keyboard may still be worth it. Data sheet at https://www.mouser.com/datasheet/2/626/ ... 334536.pdf .



Another possibility is the Omron B3F series of tactile switches, using the nice keycaps they make available in various sizes and lots of colors. The only problem is that these don't give a good way to put labels on the keycaps themselves. See the data sheet at https://www.mouser.com/datasheet/2/307/en-b32-13586.pdf .

_________________
http://WilsonMinesCo.com/ lots of 6502 resources
The "second front page" is http://wilsonminesco.com/links.html .
What's an additional VIA among friends, anyhow?

I did buy an HP-30b in part because there's a story for refitting the calculator with homebrew firmware. Indeed it seems likely this was a hidden agenda by the designers. Unfortunately the 30b was withdrawn, as there were quality control problems with the keyboard which made it badly received (IIRC). The 20b was a cost-reduced version with a cheaper keyboard, the 40b never got past prototype.

The HP-12C could possibly be repurposed but I'm not sure there's a story. The display is limited, anyhow.

The SwissMicros DM42 can also be repurposed, but it's quite expensive to start with.

Peter Nelson showed off a very nice idea for Chris Chung's HP-workalikes:





Chris uses the usual kind of miniature push buttons with a click action, and then Peter has printed the keyboard legend on card. There's enough flexibility in the card for this to work without making any cuts or flaps.

pbnelson says: