MIDI Controllable Pots

[Jim Patchell]

    I would not use an FET as a voltage controlled resistor.  I would
suggest just using a good old fasioned OTA.  Or, if you are into
experimentation, JH came up with a clever little circuit that he used in an
ADSR desgin using 4 transistors (2 npn,2 pnp) to make a control element
that has a wide dynamic range, low control feedthough, plus, it is
exponential control response.  I have not actually tried this circuit in
this application yet, but I don't see why it shouldn't work.  It very well
could be suitiable for many applications.

    -Jim

Andy Main wrote:

> Hi all,
>
> Carring on with my ASM1 design, I'm still trying to work out how to
> implement the pots located on the front panel with MIDI control.  My
> guess is to have a knob sending out grey code depending on position,
> link this via logic to a DAC and then control a FET as a voltage
> controlled resistor.
>
> Has anyone tried to do this before?  Or are there better solutions (I'm
> sure I can't be the only one who has wanted to do this).
>
> Oh and as for the patch design I've been looking at prices for switches
> and MUXs and have found that Harris do very cheap 4x4 switch arrays
> (less than a pound sterling) with not bad characteristics.  Using an
> fpga I should be able to control a huge battery of these to do what I
> want for a lot cheaper than using a larger switch matrix.  Thanks
> everyone for the input.
>
> Cheers
>
> Andy