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Old 10-17-2012, 12:55 AM
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John John is offline
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Default 128-step resolution at lower resistance ranges

D. writes:

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i want to replace a 1K analog pot with your MPA - i see the lowest you have is 10k - i need a lot of steps between 0 and 1k resistance - can i program a compensation into the 10k setup to move all 128 steps into 0-1k range?
The MPA output potentiometer values and resolution are fixed in hardware, so there is no "programming" solution to change to, say, 128 steps between 0 and 1k.

That said, you can use multiple MPA outputs in parallel to achieve a lower variable resistance value.

For example, if you connect all 4 MPA-10k outputs in parallel and program each to respond to the same MIDI message, you can 128 steps from 0-2.5k.

You can also add parallel fixed resistors, but this will result in a non-linear effective "taper".
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Old 11-07-2012, 08:21 PM
dwswell dwswell is offline
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john, thanks for your previous response...

how about this idea:
use the 8 switches on an MSA to address a resistor 'matrix' (8 resistors - one per switch) by connecting their outputs in parallel and the inputs with a constant common voltage?
set the highest resistor in the matrix (array?) to my desired maximum resistance, about 700 ohms, and arrange for the minimum resistance to be about 100ohms.

now by setting the switches in various combinations of open and closed i can effectively get 128 steps between 100ohms and 700ohms - i think...

of course if the theory is correct i still need to calculate the right resistor values to get 128 discrete steps - this seems like a pain in the ass of trial and error OR maybe there is a Formula for calculating the right resistance values?
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Old 11-09-2012, 02:49 PM
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Originally Posted by dwswell View Post
john, thanks for your previous response...

how about this idea:
use the 8 switches on an MSA to address a resistor 'matrix' (8 resistors - one per switch) by connecting their outputs in parallel and the inputs with a constant common voltage?
set the highest resistor in the matrix (array?) to my desired maximum resistance, about 700 ohms, and arrange for the minimum resistance to be about 100ohms.

now by setting the switches in various combinations of open and closed i can effectively get 128 steps between 100ohms and 700ohms - i think...

of course if the theory is correct i still need to calculate the right resistor values to get 128 discrete steps - this seems like a pain in the ass of trial and error OR maybe there is a Formula for calculating the right resistance values?
Hi dwswell, welcome.

Yes, I think that using switches combined with fixed resistors is an established approach. I think that can work. It's probably a good idea to get the lowest-tolerance resistors you can get. You might even add some trim pots so that you can make it as accurate as possible.
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