Fw: [sdiy] Minimoog "S trigger" questions

[Jaroslaw Ziembicki]

 ----- Original Message -----
 From: <synth at charlielamm.com>
 To: <synth-diy at dropmix.xs4all.nl>
 Sent: Sunday, November 09, 2003 9:45 PM
 Subject: [sdiy] Minimoog "S trigger" questions

 > a) My understanding is that Moog "S trigger" sits at 5V relative to
ground,
> and when I want the ASRs to fire, I pull this down to (close to) 0V.

 That's right, except it should be approx. 4V instead of 5V.

 > So we are talking the really simple 3-4 part NPN inverter/switch type
> circuit, with the output on the collector, and the collector tied to 5V
> via a pull up resistor--you know what I mean.  Is this correct?  Do I have
> to worry about a diode drop or some such?

 No pull-up resistor is needed! There's already one tied to +9.3V inside the
Minimoog. Just connect the collector directly (or via a 100..220 Ohm
resistor)
to the S-TRIG input, and the emitter to ground.

 > b) Is the S-trigger really a gate signal?  In other words, the signal
> stays at ground, until I release the key, then it goes back to 5V; that's
> what tells the ASR that it's time to "R".

 Yes.

 > c) Are there current issues to worry about?  Should I current limit the
5V
> that goes into the S Trigger in?  Any other sort of protection
> necessary--eg: a diode shunt to protect against trigger signal
> accidentally sent that's below ground?

 Just give a small resistor in series with the collector (see above).

 > d) On the cinch jones connector, there is a "big" blade and a "small"
> blade--ie, the male connector is polarized.  Does the 5V-->0V sig go into
> the "big" prong and a ground reference into the "small" one?  Or something
> else?

 The ground pin of the S-TRIGGER is towards the "oscillator ext. input" jack
(I've checked it with a multimeter). You connect the emitter there.

 > e) Anything else I need to know?   I would ***hate** to blow up my
> minimoog!!!!!

 If you want a 100 percent safety, drive the S-TRIGGER through an
optocoupler.

 Regards,
Jarek (S/N 11551)