Digipots with relatively high current.

[Zare]

Hi guys, since i'm new here, i greet you all

Now, we have a idea project, basically we'd like to control analog guitar fx pedals via MIDI, not only on/off, but complete control. So the first phase should be digital resistance control for controlling the pots on the fx pedal.

However, i only see maximum 1mA digipots listed on Maxim's site. I haven't found more powerful digipots of other companies via google. I think (haven't measured yet), that the current that goes through those pots will be larger than 1mA.

So if anyone can point towards more powerful digipot, or any kind of alternative. I had a brief idea to manually construct a digipot, serial connection of (n) resistors, each resistor bypassed by electronic gate. Open gate has close to infinite resistance, while closed gate has close to zero resistance, thus if the gate is open, the current will run through that resistor, if the gate is closed, the resistor gets bypassed. So you can control the resistance via signals to gates.

However, to simulate an 200kOhm 8-bit digipot i would need 128 serially connected 1.5kOhm resistors, with 128 gates, and a demultiplexer circuit that has 128 outputs. So this idea is a bit excessive.

Thanx in advance.

 

[crutschow]

Unless you are controlling large voltages the current through the pot will be small. It takes 200V to give 1mA through a 200K ohm pot.

 

[Zare]

Yes, but that 200kOhm is the pot's maximum resistance. How about minimum, let's say that the circuit operates on 9V, and on 1kOhm minimum resistance that would give 9 miliamps. Again, nine times that Maxims can handle. Therefore, the digipot could only cover a portion of the resistance range.

Again, i would need to measure those circuits or to make an computer simulation to get the exact current for both the minimum and maximum resistance value (i shooted out that 9V out of my head, it is the input voltage for most of fx pedals, but i don't know the voltage on that pot, that's dependent on circuit design...), but i fear that 1mA won't cover my needs.

 

[crutschow]

Typically a pot would have a voltage connected to one fixed end with the other fixed end grounded, and with the wiper output going to a relatively high resistance load. Thus the current through the pot is independent of it's wiper position. It's only if you connect the pot as a rheostat (the wiper connected to one end of the pot) that the wiper current would vary with position.

If you have a circuit diagram, the current can likely be calculated.