I think you could do this with:
1 x 100pf ceramic cap
1 x 100K 1/4W resistor
1 x 1N914
1 x 74HC14
Take the signal from IC7 pin 1 and pass it through the 100pf cap the other side of which is connected to the input of one of the schmitt trigger gates. Also connected to that is the 100K resistor and the 1N914. Both of which have their other side connected to ground (0 volts). The 74HC14 is connected to +5V and 0V rails.
This assumes that the signal coming out of IC7 pin 1 is a positive ramp representation of VCF + EG3 Int.
The output of the schmitt trigger gate will be high to low transition. So you may wish to place a second gate in series in order to invert the signal so that it is low to high.
The length of the pulse can be decreased or increased with different value cap and different value resistor to ground. The pulse is going to be quite short with a 100K resistor and 100pf cap. It all depends on how long you want the pulse to be.
If you need much longer pulses then it would be best to use a op amp to buffer the signal before it goes into the cap. That way, you can change the resistor/cap values without affecting the VCF signal going to the NJM filter itself.
Now what were you planning on doing with this pulse? Because I didn't quite read your posts on it earlier.
Mike
--- In korgpolyex@yahoogroups.com, "7yash" <josh.nursing@...> wrote:
>
> Would I also need an analogue switch here?
>
> --- In korgpolyex@yahoogroups.com, Michael Hawkins <korgpolyex800@> wrote:
> > Hmmm, I think I went off a little half set up on this.
> > The EG3 signal is software inserted into VCF cutoff. So you would have to accept setting EG3_INT to something above 0 (such as 1-15) and then picking up the AC signal on pin 1 of IC7 (NJM2902). You would best do this by decoupling the signal using a small value cap (<100pF) and using protection diodes of course. That would pick up the spike from the EG3 signal while ignoring the DC VCF level.
>