Problems with Digital Potentiometer

[MrWho252]

I'm having problems with a digital potentiometer. I'm not sure what it is, but I can't get the potentiometer to decrease and increase the resistance right. The resistance keeps jumping around, sometimes randomly. Sometimes it will start decreasing and then it will increase and then decrease and back and forth again and again. I really don’t know what’s wrong with it. Anyone have any ideas? Could it be that I need a debouncing circuit? But I don’t think it matters since I’m using a Function Generator or a microprocessor to create the pulses. Is there something else that I need? Thanks in advance for any help.

 

[Optikon]

I'm having problems with a digital potentiometer. I'm not sure what it is, but I can't get the potentiometer to decrease and increase the resistance right. The resistance keeps jumping around, sometimes randomly. Sometimes it will start decreasing and then it will increase and then decrease and back and forth again and again. I really don’t know what’s wrong with it. Anyone have any ideas? Could it be that I need a debouncing circuit? But I don’t think it matters since I’m using a Function Generator or a microprocessor to create the pulses. Is there something else that I need? Thanks in advance for any help.

Can you post a schematic of how it is hooked up with a part number of the digital pot as well? I'm sure there is an easy explanation.

 

[MrWho252]

I'm using the X9C103 from Xicor. Right now I don't have any schematics. I'm just trying to figure out how it works so I can see how I'm going to use it in my project. So far this is what I have hooked up to the digital pot.

Pin 1 (Inc): Clock generated by Function Generator
Pin 2 (U/D Bar): Right now it's low for down
Pin 3 (VH/RH): + Lead of a DMM measuring Resistance
Pin 4 (Vss): Gnd
Pin 5 (Vw/Rw): It's hooked up to RL
Pin 6 (VL/RL): - Lead of a DMM
Pin 7 (CS Bar): Kept Low so that no value would be stored so resistance can be adjusted
Pin 8 (Vcc): +5v

The pulse that is generated by the Function Generator is 0-3.3V

I hope this is enough information. If there's something else that I'm missing or you need clearification on please let me know.

 

[Russlk]

I don't see anything wrong with your hookup. Perhaps this URL will be helpful:

http://www.xicor.com/app_notes.php

 

[MrWho252]

I think I found out what type of problem I have. It's a walking wiper. The solution for that is that I use a pull-up for CS Bar on power up. What does it mean by that? Do I tie it to Vcc during power up? Or do I use something else? Thanks.

 

[Russlk]

A capacitor to VCC and resistor to GND. The cap pulls the pin up temporarily and the resistor pulls it down.

 

[MrWho252]

How big of a cap to use?

 

[Russlk]

A wide range of values will work, try .01uF and 10K

 

[MrWho252]

The wiper still walks. It even walks when it digital pot isn't even powered. Is that supposed to happen?

 

[Russlk]

It can get power thru the clock input, but if there is no input then you must have a high impedance that is picking up noise.

 

[MrWho252]

Is there something I can do to reduce the noise? Is it possible that the noise could be coming from a moniter or computer?

 

[Russlk]

Your connections are not what you think they are. Take it apart and put it together again. It may not solve the problem, but it will be different.

 

[Optikon]

Your connections are not what you think they are. Take it apart and put it together again. It may not solve the problem, but it will be different.

I agree, this is worth doing since its only a couple of connections. I think you can forget about external noise from monitors etc.. this sounds like wiring. Verify your supply voltages right at the pins (not on the wires going to the pins) also.

Also, if you re-wire, double check each connection right after you make one, just to be 100% sure that it is wired correctly and the device has a good power and ground connection to the supply.