In-circuit emulation of resistors and capacitors (for automated tuning)

[WSchroeder]

I would like to create or purchase controllable resistors and capacitors, with a control range of two orders of magnitude for each.  I would like to be able to change the values under computer control.  Control of R and C value with a control voltage would be acceptable.  I could work out an interface myself.

Does anybody know how to do this?  Does anybody know of a commercial product that will do this?  (GPIB or PXI bus, for example.)

This would be in lieu of a resistance/capacitance substitution boxes (with thumb wheels). 

Thank you.

[T3sl4co1l]

R/C boxes always bothered me because they're far too big, and on leads far too long, to be of any use in circuits where you would actually need tuning.

Don't throw up your hands and use a trimmer (or other adjustment), strive to understand the underlying circuit and calculate the preferred or ideal value.  Right the first time, every time.

If it's something that truly needs to have a wide adjustment range, it should probably be done electronically in the first place.  Example: RC oscillator circuit with a wide range.  Suggestion: replace R with current source; have switchable R or C to select different ranges/multipliers.  The switching can be done with more transistors, analog switches, reed relays, etc.

Tim

[unitedatoms]

I would like to create or purchase controllable resistors and capacitors, with a control range of two orders of magnitude for each.  I would like to be able to change the values under computer control.  Control of R and C value with a control voltage would be acceptable.  I could work out an interface myself.

Does anybody know how to do this?  Does anybody know of a commercial product that will do this?  (GPIB or PXI bus, for example.)

This would be in lieu of a resistance/capacitance substitution boxes (with thumb wheels). 

Thank you.

There is a GPIB controlled sets of HP relay boxes like HP Agilent 34970A or similar. Meh, for some reason nobody made resistors / capacitors GPIB box yet.

[Vgkid]

IET Labs makes programmable resistance/cap/inductance boxes.