VCF east wrap up and Oscope improvement

I think my SCELBI 8B with oscilloscope display, cassette and keyboard went over pretty well at VCF east. I did have some issues with stability of the oscilloscope display. It was very sensitive to positioning of the cables and the scope output would sometimes get flakey if you just touched the cables.

One thing that has concerned me from the beginning of the scope project, is the nature of the grounding of the different power supplies, especially the the +/- 18 volt supply for the scope op-amps. As the data cables from the main chassis include a ground wire, I knew I had potential for a ground loop problem. I think that is what was troubling me at VCF. This week, I disconnected the digital ground inputs that were coming in with the data lines. I was using them as inputs on half the strobe input gates as mentioned in a previous post. Instead I connected the inputs of those gates to the local ground which means that ground now only has a single path back to the main +5/-9 supply. It seems to have helped. I need to do some more testing to be sure the problem is totally solved, but so far, this solution looks promising.

2 Responses to “VCF east wrap up and Oscope improvement”

  1. Paul Heller says:

    I thought your exhibit was really great Mike. Very impressive work to figure out and design a board to drive the oscilloscope.

    And it was good to see you again and catch up.


  2. Jack Rubin says:

    Great stuff – sorry I missed the show but I’m looking forward to seeing your setup sometime in the future!