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analog pot to analog pot adapter. An EE question.

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SavannahLion:
If given analog pot "A" is difficult or impossible to replace then would it be conceivable to construct a circuit that adapts pot "B"? For instance, a 180 degree 10k pot replace with a 180 degree erm...20k pot. Assuming each pot is of the same type eg linear.

What about half that value? Eg a 5k pot. You would lose some granularity.

It seems to me it would be a common problem but I haven't really seen much on the topic. I can visualize a few circuits that might do the trick.

What are your thoughts?

Ed_McCarron:
Wouldn't a 20k fixed resistor in parallel with a 20k pot vary from 0 ohms to 10k?  I think you'd lose your linearity, though.

EDit:  If I did the plot right... You'd lose a little linearity.

Howard_Casto:
It depends upon the use.  Like Ed said, there are going to be drawbacks of the swap... not mind blowing, but drawbacks none the less. 

That being said, it really depends upon the application.  For a real arcade machine, particularly a classic, it will slightly alter the controls. 

On the other hand if it's for mame or something windows based, you can compensate for most differences both at the joystick calibration in the control panel and within mame itself.

danny_galaga:

--- Quote from: Ed_McCarron on May 31, 2011, 10:39:24 pm ---Wouldn't a 20k fixed resistor in parallel with a 20k pot vary from 0 ohms to 10k?  I think you'd lose your linearity, though.

EDit:  If I did the plot right... You'd lose a little linearity.

--- End quote ---

Great idea! Your smart 'n' stuff!

SavannahLion:

--- Quote from: Ed_McCarron on May 31, 2011, 10:39:24 pm ---Wouldn't a 20k fixed resistor in parallel with a 20k pot vary from 0 ohms to 10k?  I think you'd lose your linearity, though.

EDit:  If I did the plot right... You'd lose a little linearity.

--- End quote ---

That's why I picked 10k/20k as an example, math was easier. :)

Yeah took me a couple of hours yesterday to figure out how to pull out the graph tools at work yesterday but that's the same graph I came up with too.

IRT @ Howard_Castro

The thought came to me as I was reading a repair article for the 2600 paddles. The solution to sketchy pots is to dissassemble the pots, remove the lubrication grease, clean, the reassemble. This struck me as a one time repair as the grease probably served to reduce wear on the contacts. With no grease, those contacts will will wear out permanently, no more repairs afterwards.

My Hang-On cab may need to have its pots replaced too. They're hard to pinpoint with some people since pot manufacturers changed their nomenclature in a confusing manner after the 80s so what was a Type B then is not the same as a Type B now.

so I got to thinking about what kind of alternative solutions might exist.

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