adding hysteresis to a 4069 inverter

[dragonfrog]

I'm planning to make Rene Schmitz's 3-phase LFO (http://www.uni-bonn.de/~uzs159/).

One thing about that circuit that seems odd to me is that it uses a whole 4093 for just one NAND gate, and ties the two inputs together to turn it into a NOT with hysteresis. He also only uses half a 4069 - so there's three NOTs w/o hysteresis sitting around unused right there.

So, my question is, couldn't you get a perfectly adequate NOT with hysteresis by sticking a couple of diodes and a small cap to ground in front of the input to a 4069 gate? It seems to me like it ought to work, but then Mr. Schmitz is much cleverer than I am, so perhaps he chose to use the 4093 for a good reason...

(I realize my drawing would have Vh of only about 0.7V, whereas a 4093 with a 15V supply should have around twice that. using two diodes in each direction should get reasonably close.)

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inverter.png
Description:	The circuit I'm thinking of actually uses a diode and a current sink to make a sawtooth VCO, but this drawing is just to get the idea.
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[richardc64]

Man, some of you guys must be psychic. rpocc posted a 3-inverter schmitt trigger in the "interesting circuits" thread.

http://electro-music.com/forum/post-281378.html#281378

[dragonfrog]

Ah, that make sense - just like in Rene Schmitz'z 4069 VCO.

Which makes it seem all the odder to me, that he would use 1/4 of a 4093 to build a sawtooth core VCO with which to drive a phase shift oscillator built around 1/2 a 4069 - when he's got another circuit on his own site that uses 1/2 a 4069 to build a sawtooth core VCO...

Well, nothing for it but to try it out

Thanks Richard

[hexagon5un]