HP-19C Repair Odysee

[PANAMATIK]

Hi Tony,

Indeed the HP-19C PIK also generates a PWM modulated signal on all 7 print pixels for controlling their intensity. This is done by gating all pixel signals R1-R7 with the STB signal. The STB (PIK/Pin 28) signal is a continuous 10kHz signal, generated by an external oscillator, with normally 50:50 Duty cycle, if battery is fully charged. It increases the duty cycle when battery gets low. The signal level of R1-R7 is 1V, which fully switches the driver transistors without base resistor. In the newPIC I will add base resistors to get the same base current with 5V levels. The gating will be done by external NAND gates and I will generate a STB signal internally on the CCP1 PWM output. The PIC16F1519 has capability to measure the actual battery voltage and adjust the duty cycle of the STB signal. Then intensity control will still work even when the HP-19C STB signal is faulty or not generated at all.


screenshot of print pixel R1 and STB intensity control (original HP-19C PIK while printing).

Getting closer and closer to the final concept.

Bernhard