Potentiometer signal smoothing

[opamp]

Hello!
I need to smooth voltage signal from potentiometer with op amp. Can i do it with op amp active low pass filter? But my circuit have some limitations. Single supply op amp and maybe rail to rail. Supply voltage is 5V. Signal from potentiometer swings from 0.5V to 4.5V What op amp could i use? Please provide some guidence or some sample circuit.

 

[audioguru]

Why not simply connect a capacitor from the wiper of the potentiometer to ground?

 

[JimB]

Recently I needed a rail to rail op-amp which would work from a 5v supply.

I settled on the MCP6042, which is a dual version of the MCP6041.
One of these may do what you want.

JimB

 

[opamp]

Simple rc filter is not good solution. i cannot find mcp6042 and mcp6041 could i use lm324 or mc33204 like on picture?

 

[MikeMl]

Your signal really isn't coming from a potentiometer, is it? If it were, you should simply replace the pot...

 

[audioguru]

Why don't you look at their datasheets?
The inputs of an old LM324 quad or LM358 dual opamp do not work if they are within 1.5V from its positive supply voltage as shown on its datasheet. Its output does not go within 1.2V from ground.
I did not look up the MC33204.

 

[opamp]

Thanks for reply

 

[crutschow]

If you explained what you are doing with the pot signal we can give better answers.

 

[Wade_Hassler]

Simple rc filter is not good solution. i cannot find mcp6042 and mcp6041 could i use lm324 or mc33204 like on picture?

"Simple rc filter" is a good solution.
The potentiometer itself can be (most of?) the 'R' part: the 'C' part can be as large as need be without adding too much time delay.
With a potentiometer, the time delay is close to irrelevant: dozens/hundreds of milliseconds will be undetectable.

Also, if your supply-voltage is for sure to be 5 V=volts, try LMV324. Superior in all respects and 23 cents pricier.
**broken link removed**

 

[Tony Stewart]

The quality of your pot is important. Many now use very thin metallized plastic film rather than cermet, so they film metalization flakes off and gets pitted if there is any current surge, making the adjustment very intermittent and exasserbated when the cap discharges and then the contact has to charge up the cap. .. which is why a small cap and bigger R filter is better for wiper reliability. THese film trimmers and pots are rated for very low power and can easily melt when near the extreme setting with a large cap load.

 

[audioguru]

Texas Instruments says the LMV324 and LMV358 are obsolete. Their datasheet says their inputs do not work when they are within 1V from the positive power supply voltage.

I forgot to say that their output has a fairly high noise level.

 

[audioguru]

A pot makes a crackling sound output (from tiny sparks?) when it has DC on it and it is adjusted.

 

[Wade_Hassler]

Texas Instruments says the LMV324 and LMV358 are obsolete. Their datasheet says their inputs do not work when they are within 1V from the positive power supply voltage.

I forgot to say that their output has a fairly high noise level.

It's the LMV324-Q1 that went obsolete: Digikey claims to have ~100K of the non-obsolete parts left. And yes, the input can't exceed 4.2 V or -.1V. Dammit.

 

[Mosaic]

Flaky pots can be a nightmare. I had a 100K full size unit go flaky ...while NOT being moved. It was used for the set point of a control loop. It caused all kinds of headaches and blown MOSFETS downstream. It would work when you set it but go flaky a little while after.

Change the pot. Also if it isn't a voltage divider output, but just a rheostat, tie the wiper to the opposite pin from ground to reduce 'floating' probs from the wiper in motion.