Pot jitters during ADC capture

[Demon]

SOLVED: Henrik figured it out, this 18F26K22 doesn't like 10K pots on ADC.

https://www.picbasic.co.uk/forum/sho...893#post155893

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Posts moved from here: https://www.picbasic.co.uk/forum/sho...or-adc-reading



Henrik,

Do you think your routine would help potentiometer jitters?

I have new slide pots that have random jitters along the entire range of motion. ADC readings seems to vary by 10 points at times.

[Ioannis]

I have not seen Henrik's piece of code, but as he noted it is not a sort or fast one.

In the mean time, maybe you can:

1. find the reason of the jitter/noise of the pot output.
2. try getting 10 samples, sort them, keep the middle 4 or 5 ones, add and divide by 4 or 5 to get the average.

seems a lot but is fast enough for most of the cases.

For a sorting routine see here: https://www.picbasic.co.uk/forum/sho...highlight=sort and this https://www.picbasic.co.uk/forum/con...orting-Numbers

Ioannis

[Demon]

It's a hardware issue, the pots are brand new. The slider overlaps multiple resistor changes. I don't get these jitters using my rotary pots.

I read the big ADC thread:
https://www.picbasic.co.uk/forum/sho...eading-Routine

- using 10-bit ADC on 18F26K22
- take 16 readings into a table
- sort using Melanie's routine
- take the median average
- add previous average twice and divide by 3 for exponential average

...still jitters.

I placed a small cap across VSS and wiper.

...still jitters.

I tried this low-pass filter with 16K and 10uF:
https://www.instructables.com/Smooth...iometer-Input/

...still jitters.

Tried shifting out low bit.

...still jitters.

Tried shifting out low 2 bits.

...still jitters.

Tried shifting out low 3 bits.

...still jitters.

Tried shifting out low 4 bits.

...mostly stable

But now the high range only goes up to 976 or so.

I'd have to convert to a ratio of 1023 for my variables (MS Flight Sim variables=0-1023).

[Demon]

Took the average of middle 4 entries, still jittered.

Gradually dropped off low bits until I was down to 6 high bits.

It jitters a LOT less. It's at a level that would be acceptable.

I guess that's the price I have to pay when I use the "most affordable new pots from China".

[amgen]

did you do a test with a different regular pot instead if slider, and did you try, say a, 1 microfarad across Vss and slider tap ?

[Demon]

did you do a test with a different regular pot instead if slider, and did you try, say a, 1 microfarad across Vss and slider tap ?

I had made tests a few days ago using various ceramic and electrolytics up to 10uF with no improvement.

I have one last thing to test, gonna report back.

[Ioannis]

Gradually dropped off low bits until I was down to 6 high bits.

Well, 4 bits down means the jitter is max 15 counts of the ADC... This is too much!

Cannot understand how can a pot have so much bad connection of its wiper... If you use this port in audio circuit, it should make a lot of noise! Even old and dusty pots, if stationary, do not have such behavior

But then you said that with rotary pots you do not observe any jitter. All the sliders do the same?

If yes, better dump them and get decent ones.

Ioannis

[HenrikOlsson]

Sorry for the delay but the thread is a decade old so....
What's the value of the pot in question? Link to actual product or datasheet?

It certainly sounds like a hardware issue. If it works OK with a rorary pot, of the same value, then the slide pot is crap - obviously.

But, do you really NEED 10 bit resolution? Even if you throw away say 3 bits you still have 127 discrete values. On a 70mm long pot that's about 0.5mm movement. If the sim software expects 10bits then just shift the value left three digits.

[Demon]

...All the sliders do the same? ...

I have 3 sizes, 45, 60 and 100 mm, all the same mediocre performance.

[Demon]

if the slider pots had been sitting around for a few years then the wiper windings could be tarnished (not good electrical contact). might be able to spray/squirt some contact cleaner and vigorously move slider to get better contact

Nah, not even new-old-stock.

These were built for me.