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View Full Version : Solved Joystick problem. Do pots go bad?



Ragtop
03-02-2012, 02:31 PM
I am having a capacitance problem with one of the pots on this thumb joystick from Sparksfun that uses two pots for x and y position. When I just touch the joystick the RC value jumps on that pot but not the other one. I tried unwiring the "bad" pot to see if the other pot started displaying capacitance, it did not. Tried switching the wiring of the pots to see if it was my RC circuits, but the problem persists with the same pot no matter which RC circuit it is on. I tried grounding the metal frame of the joystick casing.

Do pots go bad?



http://youtu.be/n1lBZS_GrMk?hd=1

Phil Pilgrim (PhiPi)
03-02-2012, 03:12 PM
Yes, pots can easily go bad. When the resistive element gets dirty, the resistance between it and the wiper can jump around a lot. That's what causes "static" in volume controls. Hie thee to RadioShack, and get some aerosol contact cleaner (http://www.radioshack.com/product/index.jsp?productId=2103700) to use on your quirky pot.

-Phil

Ragtop
03-02-2012, 05:35 PM
12 bucks a can. How often do they get dirty? Can it be used for anything else?

Duane Degn
03-02-2012, 06:27 PM
You might want to try just some compressed air first.

I think this type of cleaner used to be a lot less expensive back when they didn't know it was causing a hole in the ozone layer.

Circuitsoft
03-02-2012, 06:52 PM
I think it can be purchased cheaper at car parts stores.

skylight
03-02-2012, 08:40 PM
Colclene orange was brilliant for cleaning pots till it was banned in the UK, replacement stuff was rubbish and left a residue.

W9GFO
03-03-2012, 01:47 AM
I have not had much luck with SparkFun's thumb joysticks. From center they would increase in resistance both directions. One direction it is supposed to do that but not the other, it would increase in resistance before dropping off, requiring a very large null zone in order to make it useable.

The joysticks from Parallax are much better quality IMO.

Ragtop
03-03-2012, 12:07 PM
Yeah, I am thinking about changing to the 5 position switch (http://www.parallax.com/StoreSearchResults/tabid/768/txtSearch/joystick/List/0/SortField/4/ProductID/615/Default.aspx)

as it is more suited to my application. Just need up/down/left/right for my TV remote project. I was just trying to make do with what I had on hand.

I haven't had that resistive problem with this joystick (yet). It centers 72-80. Goes down to 1 and up to 245, but one just goes crazy if I touch the joystick.

Phil Pilgrim (PhiPi)
03-03-2012, 02:52 PM
Another thought: cold solder joint. Inspect the joints where the pot is soldered to the PCB, or just touch them up preemptively.

-Phil

T Chap
03-03-2012, 02:59 PM
Find a sealed pot, like Bourns, and it will have less issues. Fry's, etc.

Ragtop
03-07-2012, 05:16 PM
Finally got out of the house and got a can of QD electronic cleaner from Walmart's automotive section.

Still seeing movement of the RCvalue when I touch the joystick, but much smaller spikes. May try another spray of it later, but
right now it will do since I am only using the extreme positions as commands.

erco
03-07-2012, 05:19 PM
Pots inside servos go bad over time, too. Changes their feedback and output position for any given input signal. Less critical in RC applications than robotics, where long-term calibration to a particular value is needed.

Such as a robot arm, for instance... :)