Author Topic: use low resistance wire as potentiometer in ADC  (Read 1274 times)

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Offline topcatTopic starter

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use low resistance wire as potentiometer in ADC
« on: May 28, 2018, 07:15:54 am »
Hello,

I am building a little application where I want to seance to position of a wiper on a long wire (approx 1m).
It a copper wire so resistance is very low.

Ideally I could just connect one end to GND and the other to VCC and directly input the moving seance arm into the ADC input.
But obviously current flow will be too high in my wire.

Is there any simple approach for this?
Adding a current limiting resister changes the voltage gradient across my wire, and I really want to have good dynamic range maybe not the whole 10bits but close to 0-5v

Thanks Dag.
 

Offline timelessbeing

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Re: use low resistance wire as potentiometer in ADC
« Reply #1 on: May 28, 2018, 08:21:32 am »
Well if you're going to summon spirits from the realm of the dead, I think silver is the appropriate metal to channel energy.
 

Offline tszaboo

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Re: use low resistance wire as potentiometer in ADC
« Reply #2 on: May 28, 2018, 08:35:13 am »
You could place the potentiometer in a bridge (with a series resitor), called wheatstone bridge, and then amplify the signal with an instrumentation amplifier. Or use an ADC with a PGA in it. Dont expect to solve this problem without adding components.
 

Offline Brumby

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Re: use low resistance wire as potentiometer in ADC
« Reply #3 on: May 28, 2018, 08:39:32 am »
My first thought drifts towards Nichrome - but I don't know if that will be a suitable Medium.
 

Offline Gyro

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Re: use low resistance wire as potentiometer in ADC
« Reply #4 on: May 28, 2018, 08:42:43 am »
Why does the wire need to be copper? It will have poor resistance to mechanical wear, which will degrade its linearity.

Also Copper has a high temperature coefficient (it will get hot), so it won't be linear near where it is terminated (cooled) at the ends and probably at the wiper too if it has any thermal mass.
Best Regards, Chris
 

Offline topcatTopic starter

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Re: use low resistance wire as potentiometer in ADC
« Reply #5 on: May 30, 2018, 08:59:53 am »
Thanks for the help.
I am going to just start sensing as the undead were interfering with my measurements.

Anyway I don't think Nichrome has high enough resistance for me, none that I could find to buy did anyway.

So I think I do as NANDBlog suggested.
 

Offline jeroen79

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Re: use low resistance wire as potentiometer in ADC
« Reply #6 on: May 30, 2018, 01:00:01 pm »
What is the background of your question?
What are you trying to accomplish?

Does the wire have an existing function?
And do you want to use it as a potentiometer for a secondary function?
 

Offline JS

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Re: use low resistance wire as potentiometer in ADC
« Reply #7 on: May 30, 2018, 03:07:03 pm »
You should probably use a 4W resistance metering system, but you will need to amplify the signal after the wire. 5V across 1m of cooper wire is never a good choice, if the wire is small enough to have reasonable current draw it will overheat. If it's thick enough current will be too high anyway for the wire, even if you can supply it and you can afford the energy loss.

JS
If I don't know how it works, I prefer not to turn it on.
 


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