[sdiy] filter cutoff and pitch manipulator idea involving joysticks

[Cynthia Webster]

Hi Milo, 

Another name for this 5-level voltage quantizer that you describe is a
"staircase window comparator"  I built a module like this years ago for
a system I made for San Francisco State University's Electronic Music lab.

The dot/bar led driver chips are a way to go,
however you're throwing away some of the circuit's resolution in keeping
the voltage levels always below the sixth LED driver channel.

It could easily seem like the joystick is not being responsive?
Perhaps you could use every other output to halve the resolution?

Maybe only five-levels, or "windows" in the control voltage are not
critical, 
but if they are... then you can do it with the AD7226 Quad eight-bit
D/A converter.  (like the LM3914 chip, this Analog to Digital converter chip
also has an internal ladder of comparators to form the staircase)

There is a circuit shown on the Analog Devices website here

http://www.analog.com/UploadedFiles/Data_Sheets/58252466AD7226_c.pdf

on page 11.

You could even have a corresponding LED light to show which of the five
windows or "steps" were active as you panned the joystick.

BTW, I'd also recommend adding a switchable inverter to each axis,
as this way the relationship between your two parameters are not
quite so etched in stone.

Best of Luck Milo!

Cynthia

http://www.cyndustries.com/






on 10/13/04 1:29 PM, Milo Barrowclough at delta_316 at yahoo.co.uk wrote:

hi everybody

i am experimenting with computer joystick controllers, dismantling them and
the like. i have discovered that both axes of the joystick controls a
separate potentiometer i.e. one for x-axis one for y-axis . i think that the
value is around 470k. i think it would be cool to modify the joystick so
that one axis varies filter cutoff and the other axis varies pitch of an
oscillator. hooking it up to control cutoff is simple enough, just tie one
end of pot to supply voltage and the other end to vcf cv input. but pitch is
more tricky. ideally i would like to have 4 or 5 pre-determined pitches,
tuned to a certain key or scale, (i.e. 5 pots) , which are switched to vco
cv input. which of the 5 pitches depends on the position on the
value/position of the joystick pot. so in practice this would mean
converting the varying voltage level from the pot into a fixed pitch (one of
5), which ever is closest. how could i do this?
i think that what i am looking for might be called a pitch quantizer.
my skills are rudimentary, so it would have to be a fairly basic circuit.
thanks





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