Work arounds
On Friday, Geoff came over. For some reason it appeared the red
LEDs in my control panel were behind the problem. When we
replaced themwith a yellow LED it seemed to work.
Geoff suggested I paint yellow LEDs with Tamiya transparent red
paint. I had no Tamiya paint on hand, so I tried putting a yellow
LED in series with the red one. This worked, too, and I already
had a bunch of yellow LEDs on hand (21a). Now the panel was
working, but needing different LED colors felt weird to me.
Finally Duncan came back from vacation and suggested adding
4.7K ohm pull-up resistors to the red/yellow/green lines (21b).
I gave this a try and it worked also.
Seeing what's happening
A good friend gave me an old oscilloscope (a very good friend).
I hooked it up to the red, yellow, and green wires and made the
following observations:
