HP97 The journey begins

[teenix]

A bit of one step forward, two steps back going on.

I placed my oscilloscope on the power in rail of my new HP-19C circuit.

I thought that when switching between Pgm and Run, the switch would maintain a solid power connection between these two positions. However, I can see a burst of noisy power spikes from ground to Vcc lasting around 20mS, and this will vary a bit depending on how fast the switch is moved.

The 60uF capacitor on the input of the original HP switching power supply probably deals with this, but on my circuit, it will cause a few headaches.

I sorted the problem, so lucky I saw this now, although a new PCB design is required.

While completing the menu software, I also noticed that one of the pins on the processor chip didn't support the function I assigned to it and I had to reassign it, so definitely need a new pcb design.

cheers

Tony