X2 Function generator

I put power to the two sections of the x² function generator. In keeping with my good fortune so far, it works. It is out of calibration, of course. The largest error is about 3.5%, though it is closer to 1.5% over most of the range. It just needs adjusting.

It works by approximating the quadratic function with a 7-part piecewise linear function. They use switching diodes to determine the segment. Like all things on the TR-20, it works in conjunction with an amplifier section. This is why it needs 14 amplifiers. There are two x² sections, one for negative input and the other for positive. You can patch them both together to support bipolar input. Both work, though I did not test the tolerance in the position section, yet.

I hooked up my homemade extender and made a pass at calibrating it. It worked just fine for the negative side, though the first two pots are at the limit (but are in tolerance). The positive side would not work with an input greater than 7.5 volts. The diodes all tested okay. After some diagnostics, I figured out it worked perfectly on a different amplifiers, so amplifier 13 appears to have a problem with larger negative voltages. I'll work on it later on.

I also hooked up two of the precision potentiometers to the 10V supply and the inputs to the plotter. It works perfectly, though I don't have a pen, yet. You can adjust the pots to move the pen on the plotter. It's the worlds most complex and precise Etch-a-sketch.