Exponential programmable resistor

[assembled]

Hi everyone!

I am trying to find a way to make a programmable resistor ranging 1R to 100k. 128 exponential steps would do perfectly, but I only can find ways of making linear steps. A simple two-pin device with selectable resistance is needed with as small number of relays as possible. Any ideas?

Thank you!

[5th element]

Both analogue devices and maxim semiconductors have quite a large selection of digital potentiometers, I assume you've looked through their catalogues?

[assembled]

Do digital pots go down to 1R? There does not seem to be any digital pots meeting requirements.

[5th element]

Originally Posted by assembled

Do digital pots go down to 1R? There does not seem to be any digital pots meeting requirements.

If it's important that you have a real 1R step in there then simply use that as the minimum that the pot can go to by adding a 1R resistor in series with the correct end of the pots resistive element. If it is absolutely necessary that the pot actually go down to zero resistance too then you'll have to add in a small relay to bypass the resistor for the last step.

I would be surprised if a digital potentiometer existed that actually included a 1R step. I mean if you've got a pot with 1024 discrete values and it's got a total resistance of 100k then you're looking at step sizes of 100R. Granted that is for a linear taper, but I can't see a log pot having a 1R step in it either.