HP-19C Repair Odysee

[PANAMATIK]

After a long time has passed, I recently remembered my unfinished HP-19C repair project. Also I remember my words, that I never again will open an HP-19C calculator, a rule which I have broken now.

In the last days I convinced myself to start with a new approach. I dont want to build two separate chips, an HP-19C ACT chip and a PIK chip amymore as in my previous concept, but a combined solution with one PIC16LF19197 processor. This is much easier to handle. I already combined the two softwares from my ACT/PIK approch and now already have a source code for the new processor, which "only" need to be debugged. My concept differs from teenix HP-19C project, which replaces both PCBs (the complete electronics). Instead I will only replace the processor board, the power supply board will be left in place but mainly deactivated. It shall be as simple as possible to remove the old main board with the new PCB. Even for the display contacts I think I have a solution which doesn't need to transfer the original spring contacts to the new PCB.

The new HP-19E board will have following features.

1.) Low Power consumption <20mA when not printing, no power consumption when in Sleep mode
2.) running on 3.3V from batteries (also 4x1.5V Alkalines possible) with low quiescent current LDO regulator
3.) Alphanumeric LED display with program steps shown as plain text
4.) HP-19C 13-digit LED display or compatible Woodstock 12-digit LED Display if the original is not available
5.) printing with the built in thermo printer and to external Infrared printer HP82240B
6.) Real Time Clock with Time Date Alarm
7.) Beeper (also programmable as instruction)
8.) 512kB non volatile SPI Flash or pin compatible Fujitsu FRAM for many user programs
9.) optional HM-10 Bluetooth BLE module on board for PC communication (upload download programs, updates etc.)
10.) optional GPS module on board for satellite communication
11.) Printer intensity can be set by software key sequence

The features will follow the Woodstock LP (HP-29E LP) set of features.
Find attached a preliminary schematic for the new HP-19E main board. All components for the prototype board are ordered and I will start debugging in a few days. If the software works on the prototype board, I will design the PCB layout in a few weeks.

One of the reasons for my new start with the HP-19C repair project is that I had an HP-19C calculator from "Harald" for about two years and still couldn't repait it. Last week I made a new try and replaced the RAM chips by some spare RAM chips from an HP-27 calculator. After a first success I could enter program steps again, but it was not reliably working, then after soldering also the second RAM into the original board, nothing did work any more. Something must have happened with these sensible old chips or the second HP-27 RAM was defective. This calculator also has a power supply problem and needs >5,3V battery voltage to power up.

Now I think a new PCB will possibly give it a new future.

Bernhard