Variable programable resistor

Question

Hello all,

I need to creat a cheap device under 50$ that can simulate a Digital potentiometer. A digital potentiometre is also know as programmable resitor and it alows the user to change it's value from a PC.I found some uC that can simulate a digital potentiometer. My biggest problem is that I can't use the because they don't have a good rezolution. I need a device that can go from 0 to 400ohm whit a rezolution of at least 1 ohm (it whould be recomanded to be 0.5ohm). This device I need to creat some test in a lab enviroment so they need to realy good.

At the moment whe have some devices bouth they are realy expensive. I need 8 variable resistors and the price of one devce that simulate one resistor is around 250$. An this is to much.

My device is power by a variable pover supply from 0 to 36v. Has any one an ideea how cold I creat a divece to do this?

lpetacchi · Answer

In my opinion, the easiest way is to use 2 DACs for U11 and U12. Reading U voltage with an ADC, you can program DACs with very high resolution. PSOC1 fits the task.

You only need to formally derive U11 and U12 as a function of R11, R12, with simple circuit analysis.

jvdberg@ieee.org · Answer

I assume the Rv resistors are the coils of a crossed coil meter.

This is a wheatstone bridge.

Try this schematic. The pot has to be adjusted once for middle range. You can start with an other voltage source to drive the left transistor. If it works satisfactory, you can add the DAC and buffer circuits..

lpetacchi · Answer

Just a suggestion: close the op-amp feedback on Q1 (Q2) . This way you don't need a (matched) differential stage; remember to invert the connections to opamp inputs and check for stability.