HP97 The journey begins

[teenix]

Another "yay" moment.

The PIK chip is responsible for detecting the print head in the home position at switch on. If it is not home, it will try to return it there ready for use.

My "PIK" chip had this function enabled today. I plugged in the motor and home switch wiring, moved the print head away from home and turned on the power. This all worked in code simulation, and luckily it worked in the real world too.

If the print head does not return in a certain amount of time, a message appears on the display, the printer is shut down and it is flagged as unusable until the next power cycle. In this state, regardless of the printer switch, or if any print function is enabled from the keyboard, the printer will not work.

If this printer is known to be faulty, a user can set a menu item to disable the printer as well.

After some playing around, I realized that the IDC pin CPU board to Printer board connector I have is unsuitable. It takes too much pressure to insert or remove it and I fear this will cause problems. Loosening the pins helps reduce the problem, but then the contacts become "iffy".

I sat down yesterday and redesigned both boards, so apart from the print head connections which have to stay there, the only others are 3 wires connecting the battery and switched print head power to the CPU board. You should be able to open and close the calculator fully without a problem. The Home, Motor and charger wiring now connects to the CPU board, but this doesn't matter.

Next is the printer operation where I have to start energizing the heads. It looks good on the scope, so it should print ok. There will be some fiddling with printed character spacing depending on the speed of the motor. This will be a hardware tweak, but the software also allows the user to set the print speed and intensity.

cheers

Tony