> From: "Dave Bradley" <daveb@...>
>
> There's nothing much easier in Synth-DIY land than taking a bunch of pots
or
> joysticks or buttons, sticking them in a box with a power supply and some
> jacks, and wiring them up so that they output voltages when you twist or
> poke them.
>
> Piece of cake. Just keep the voltage levels down to MOTM specs.
Right Dave, but a stooge like me will probably need some help. I have a 2U
MOTM panel planned with a joystick protruding. I already have two
joysticks that look perfect for the job. They have the two pots built onto
the side with centering adjustments. And, of course, it has that &∗%$#
button on the end and is spring loaded. Here is what I was thinking:
Two panel pots in addition to the joystick for EACH axis. One would be
"range" and one would be "zero trim." I think the range pot would need to
be a dual pot that added resistance (in series) to both sides of the
joystick pot at the same time. The more resistance in this pot, the less
voltage across the joystick pot and therefore the smaller the CV output
range. The zero trim pot would be of much smaller value and stuck on one
side (in series) with the joystick pot. Once the range was set, this pot
would adjust to joystick center return point to zero voltage to compensate
for slight differences in the dual pots. A disadvantage is that the zero
trim pot would also have some effect on overall range. I see a couple of
ways around that. 1, make it a dual pot also (add to one side and subtract
from the other). Or a voltage adder to the final joystick output, ala MOTM
fashion on its CV voltage adding inputs. Come to think of it, the range
pot could also be done that same way and it would not have to be a double
pot. (stooge thinking aloud here waiting for the guys that REALLY know to
correct me).
So controls are: X-axis range, X-axis trim, Y-axis range, Y-axis trim.
I would want some way to reverse the output voltage. You could use a DPDT
switch to reverse the DC supply voltage to the joystick resistor. However,
what would REALLY be cool was to have opposite voltages available for each
axis at the same time. So, have the joystick voltage drive an inverting
amp and have 4 output jack X volts +, X volts -, Y volts +, and Y volts
-. This would eliminate the need for a reversing switch.
Which brings up a basic QUESTION I have for the DESIGN guys: If you used a
simple voltage divider circuit or CV adding like on the inputs of some MOTM
modules, would you need to buffer the output anyway with an opamp? This
would make the dual opposing voltage idea almost automatic.
Now, that DANG button. I had two ideas for it. I think it would be cool
to have it be dual function (switchable).
Function # 1: zero voltage adjust test - easy. SPST normally open (mine
are). Use that contact to short the X or Y output CV to ground. You could
very easily "trim" the CV out to zero using the pushbutton as true zero
test. toggling would allow for "by ear, on the fly" adjustment.
Function # 2: Generate a gate a trigger when depressed.
OK, I'll shut up for now. My panel now has joystick, 4 pots (as above),
one switch for button function, 4 CV outs, and one trigger and one gate
output. Looks like it would all fit on a MOTM 2U panel.
OK idea guys, shoot.....
LH