HP-42S "reinterpretation"

[pito]

(05-04-2015 01:54 PM)robert rozee Wrote:  .. a standard 1602 LCD module for the display (16x2 characters, HD44780 based). 2xAA cells for power directly to processor and LCD module. a PIC32MX170F256B (28-pin DIP package) to run it all, with 256k flash and 64k RAM on board. and running a derivative of Free-42 as the calculator firmware.

HD44780 based LCDs require 5V Vcc.. Also the display is not graphical one, but 2x16 chars.. An SPI color 1.8-2.4inch tft LCD will do better, power consumption <<1mA with backlit off. Backlit needs a few mA (the same with HD44780). (Btw HD44780 LCDs do not require negative LCD bias..)

That PIC32 with 64kB ram - double check whether the free42 would even compile straight with 64kB of ram especially with decfloat (I compiled a double precision basic written for pc to pic32MZ (w/ 512kB of ram) and the max source I could load was something like 500lines.. - it depends how it is written..)

Also consider the PIC32MX170 takes ~0.5mA/MHz (there are chips with 150-200uA/MHz but ARMs).

I would add a HC-05 BT module to the serial i/o for upload/download and an sdcard socket (good for your mmbasic too).

All the components - LCD, LCD backlit, BT, sdcard, 24LCs would need a high-side pmos switch (thus you could switch them off to save power).

What I miss is an RTC.

Otherwise I think the 42s is the best HP "calculator" ever made. Quite surprised how it was made (sw-wise) considering mid 80ties design. Especially the keyboard design and menu is great, even I would replace the orange button with <- clear one. Quite happy to have it running on my galaxy S2 .