[sdiy] joystick pots

[Grant Richter]

Hi Eduardo,
> 
> I ordered 4 of these joysticks along with the stick knob/handle from
> meci.com, along with a few toggle switches.  nice price too!!
> 
> I was thinking of making a couple into a sort of "modular" joystick,
> 
It could almost tempt you into making a product....(sigh)
Too bad labor is 10x the cost of parts.

> say, a jack for each pin of the pots (totalling 6) with the extreme pins
> switched to pos. and neg. voltage, maybe with an attenuator pot or a switch
> for each pin to limit the voltage range.
> I was thinking of this incase I would want to use the joystick in part as an
> attenuator,  patching ground to one pin, signal to the other and then output.
> I thought it mught be interesting to do this on one axis and have voltage on
> the other.

This is like a "coefficient potentiometer" from an analogue computer. The
original computers used a 1K potentiometer for low impedance. Not surprising
then that synth modules use a 1K output impedance.

Coefficients are usually referred to ground. So you only need two jacks per
pot. The third terminal will almost always be ground. 150K is too high an
impedance, you will need to buffer it with a voltage follower. A simple
design is at:

http://www.musicsynthesizer.com/Joystick/1209.htm

which used the MECI joysticks. Plan on putting the trigger buttons nearby. A
better design is to use an op-amp in the voltage follower configuration (but
requires +/- supply).

If you insert a switched jack between Vdd and the top terminal, you can
input a control signal, then attenuate and buffer it. Handy for oscillator
modulation with simultaneous modulation frequency and depth control.

Making +/- voltage joysticks is difficult without a center detent. Zero is a
very important number in math since 0 x anything = 0. Using +/- joystick
makes it hard to shut modulation "off". The Wiard designs always use 0 at
the bottom/left for a definite off position - your mileage may vary,
avant-garde musician don't like turn-offs (snort, chuckle, cough, wheeze)

#4 x 3/8" flat head sheet metal screws will thread into the plastic body and
mount the joystick to the panel. Recessed screw heads are recommended to
prevent cutting your fingers on the screw heads during very passionate
performance.

"Each generations illusion of 'newness' is the oldest fossil of all".
- Jeff Chase