I would like to build a Voltage or Digitally controlled resistor for controlling older analog equipment from a micro or PC. The only methods I know of that can get this done is using digipots, jfets/mosfets, or relay controlled resistors.
My application needs to control a PSU remote port which requires 1k ohm to produce 1v on the PSU out put. This means I need 1ohm to 20k ohms with a 1ohm resolution, which imeaditly rules out a digipot due to resolution. Using a relay controlled decade box is a pretty decent way to get good acurracy and resolution, but it is kind of clunky. This leaves the FET route, I've never actually used a FET as a replacement for a rheostat, so is it possible to get the range I'm looking for and set it in 1ohm steps? There are also sense lines I can use to read the output voltage of the PSU and use that as a feedback for the FETs gate voltage which I'm guessing would be controlled by a 16bit dac in order to get good resolution. Only question is if it is possible can anyone recommend a FET (peferably one fairchild makes) low power is just fine as long as it can handle 25v.
Maybe there is another way to go about this, besides a stepper/pot and the ways I listed above. I seems like digitally controlling resistance at 1ohm steps would be more common that I thought!