VCO Working

A project log for VGA VIDEO SYNTH

vga analog video synth

JulienJulien 06/22/2018 at 14:060 Comments

This log will be heavy on pictures. Sorry for your internet bandwith.

The lzx cadet vco is built and working. Really nice piece of circuitry. I added an inverted output to both waveform (square and triangle) . I had some oscillation at  42Mhz which was the ringing of the 74HC14 inverter at the output of the LM6172. The noise also fedthrough the other waveform (both inverted output share the same package) .

 10pF capacitor in the feedback loop of both op amp solved the issue.

This vco was intented for TV usage. Nonetheless I guess it'll work as well with VGA. I built a small test jig for two oscillators:

behin the panel, it's the video splitter board. It split the PAL video signal from its syncronisation and recombine it afterward. It allows to input an external 1v dc signal and it displays it on the screen (using the sync signal from the input pal signal).

On a tv, this setup gives nice black/white patterns, vcos can also be modulated with video signal !

Now that the vcos are good I need to test them with a vga screen (just to be sure) build the last 3 of them, the envelopper follower and the second part of the output circuitry.