[vcf-midatlantic] SCELBI Oscilloscope/Keyboard Interface Updates

[Mike Willegal]

Hi Joseph,

I don’t know much, if anything about "X-Y” displays and how they may differ from a typical scopes.  Because I’m only going to 20x5, the scope screen is actually plenty big enough.   

Here are a few details on the issues I hope to improve upon over the next couple of months.  The scope interface has three outputs.  Two are the X-Y vectors each of which is a voltage value offset.  The third is a blanking signal.  First problem is that my Tektronics 465 isn’t responding fast enough to the blanking signal.  There are some limitations in the 465 blanking input, in that it’s capacitor coupled, and along a with resistor in the scope interface blanking circuit it is creating your classic RC time constant delay. I’m going to see if I can reduce a key resistor value a bit in order to reduce this effect or find another way to drive the input a bit harder.   The second issue is that the analog board op amp circuit isn’t really calibrated correctly.  The design uses an op-amp integrator scheme to “paint” the vectors on the screen.  When the circuit is reset to top left, in order to repaint the page, the op-amp outputs drift a bit after that before they “settle down”.  I haven’t looked into this in detail, but I’m pretty sure that I can fix this with some resistor value tweaks to the op-amp integrator circuits.

regards,
Mike Willegal