Linear variable resistors behaving logarithmically

Hi all,

Just have a quick query.

I'm driving a me arm robot using linear variable resistors, but find that the resistors have a very slow response until the voltage gets to approximately 2.4 volts coming out of the resistor, then a tiny amount of rotation on the variable resistor takes it straight up to 5 Volts output.

For those that don't know, the me arm robot is this:
https://www.google.com/search?q=mearm+robot&ie=utf-8

I have confirmed that they are actually linear trimpots by hooking one to a multimeter.

Whilst I am a Process Engineer by trade, I am not familiar with the Arduino boards to the standard I would like.

Any help or guidance on fault finding which you can provide would be greatly appreciated.

Best regards,

Meant to add in the above that I am teaching this project to 30 15-year olds.

My current suspicion is that the pins declared as outputs in the board may be interfering with the resistance and it's somehow upsetting the balance, but it's just a hunch with no proof.

My next line of attack is to separate the power to the servos from the power to the board to try and isolate the board as much as possible

Andrew,
You are asking us to help you solve a problem with either your software or your circuit without showing us either. There are some very clever people on here but I do not think a single one of them is telepathic.

Please read 'how to use this forum - please read', the post the information requested.

Thank you.

Andrew_F_In_Australia:
Any help or guidance on fault finding which you can provide would be greatly appreciated.

I'd run the very first tutorial in the list to print out the analog values and see if they vary as expected.

(In the IDE go File > Examples > 01. Basics > AnalogReadSerial)

But also provide a schematic of what you're doing along with your code, as already suggested.)

PerryBebbington:
Andrew,
You are asking us to help you solve a problem with either your software or your circuit without showing us either.

If you verified the resistance and you felt that it was linear then the resistors should be good.
but you can verify the 2.4v jumping to 5 volts using a power supply.

ditto with supplying a circuit diagram of some sort.

I'm driving a me arm robot using linear variable resistors

Just a guess, but if unless you use all 3 terminals wired as a "normal" potentiometer, a "variable resistor" (using 2 terminals) usually won't give you a linear voltage.

Post a wiring diagram.

Volume control potentiometers have a logarithmic response curve (resistance versus shaft rotation or position), because human hearing responds logarithmically to sound pressure amplitude.

Hi,

Can you please post a copy of your circuit, in CAD or a picture of a hand drawn circuit in jpg, png?

How are you wiring your potentiometers, what voltage do you read at the analog input pin as your pot turns?

Have you got just a simple bit of code that just looks at the analog input and serially prints the AtoD result?

Thanks.. Tom... :slight_smile: