Strange problem with potentiometer

Dear all,

I have a problem with a 1 kiloOhm potentiometer which is integrated in my stepper motor (for imaging).

When I connect it to Arduino and try the AnalogReadSerial example, the maximum voltage I measure is 3.8 Volt. Beside this, the digital value goes from 1023 to 249 or something like that. So it skips the first 249 units (or 249 * 0,0049 = 1,2 Volt).

I tried it also with only a 9V battery to exclude my Arduino doesn't work well. However, the same fault. Around 7V it goes to 0V again. However, I still measure the 1k Ohm at 7 Volt and 0 Ohm at 0Volt.

Yesterday everything worked fine with my Arduino in combination with the potentiometer. I measured from 0 until 5 Volt. Unfortunately this morning I got these problems.

Hope anyone could help me.

If you exposed the analog input to a voltage greater than 5V, you probably damaged the Arduino.

Please try to explain, in a different way, what the following statements mean and exactly what you did. Post a simple wiring diagram.

Around 7V it goes to 0V again. However, I still measure the 1k Ohm at 7 Volt and 0 Ohm at 0Volt

jremington:
If you exposed the analog input to a voltage greater than 5V, you probably damaged the Arduino.

Please try to explain, in a different way, what the following statements mean and exactly what you did:

I think you don't understand me.

First thing I did:
Potentiometer to +5V Arduino, ground and analog input. With the example AnalogSerialRead I read the values and measure the voltage over the analog input with a multimeter -> from 0 to 5 Volt.

Today I did this again and I measured 0 to 3.8 Volt and converted values 239 to 1023 (I thought yesterday from 0 to 1023 but did not pay attention to it). And yes there is still 5 Volt from the Arduino.

Second thing I tried:
Connect the potentiometer only to a 9Volt battery and measured again the voltage over the output voltage pin of the pot -> 0 to 7 Volt instead of 0 to 9 Volt. However, the resistance is still from 0 to 1kOhm.

Is my potentiometer broken or what is wrong?

DO NOT EVER EXPOSE the analog input to voltages greater than 5V.

Do you understand this point?

jremington:
DO NOT EVER EXPOSE the analog input to voltages greater than 5V.

Do you understand this point?

Yes haha but I didn't do this??! Please READ...

Connect the potentiometer only to a 9Volt battery and measured again the voltage over the output voltage pin of the pot -> 0 to 7 Volt instead of 0 to 9 Volt.

Good luck with your project!

If that really is the potentiometer on its own with no connection to anything except the 9V battery and the meter then it is bad.

But you did say it is "integrated in my stepper motor" which makes me think the potentiometer must travel over 360 degrees. Do you have a link to this integrated stepper and potentiometer?. I wonder if there is something about the stepper motor that is preventing full movement of the potentiometer.

Steve

jremington:
Good luck with your project!

Yeah, what's the problem of connecting only a potentiometer to a 9V battery without microcontroller? Only to rotate it and measure the output voltage???

slipstick:
If that really is the potentiometer on its own with no connection to anything except the 9V battery and the meter then it is bad.

Steve

Yes it is. It is only mounted on the shaft of the stepper motor (integrated in a housing, that's what I mean with integrated). So it could measure the position of the steppermotor shaft.

slipstick:
But you did say it is "integrated in my stepper motor" which makes me think the potentiometer must travel over 360 degrees. Do you have a link to this integrated stepper and potentiometer?. I wonder if there is something about the stepper motor that is preventing full movement of the potentiometer.

Steve

No information about the steppermotor or potentiometer itself. I only have a connector diagram and know the steppermotor is bipolar, the potentiometer is 1 kilo Ohm. And from the original manual this steppermotor and pot is used for, I know the following of reading the position value from the potentiometer:

"Channel 73 is used to measure the voltage from the servo valve from 0 to 4.096 Volts. It is then converted to a position percentage from 0-100% (+/–1%) to provide an indication of the servo valve position. Thedefault coefficient for the channel is –24.4142 and should not be altered."

It would really help if you could give us a diagram of how you are connecting this 1k pot. Does it have three terminals or just two? When you say you "measure 1k", from where to where? All of your descriptions give me the impression that there are only two terminals, in which case, you aren't going to get a proper "potentiometer" effect. It would be more like a "rheostat", which won't give you a useable reading, without a series resistor [i.e. to make it function like a voltage divider].

So, please, come up with a diagram -- even if it's drawn on a piece of paper and photographed, or you could use something like Fritzing. But, whatever you use, make sure it's clear and comprehensive.

Please confirm the stepper motor could NEVER turn 360 degrees in the original device.

Paul

I am not sure I understand what your problem is, definitely you need to post the wiring and physical arrangement

RaceEngineer:
Yeah, what’s the problem of connecting only a potentiometer to a 9V battery without microcontroller? Only to rotate it and measure the output voltage???

What they need here are ----- photos of your potentiometer … and the way you connected things… photos, and a circuit diagram.

Also, maybe a good idea to have some spare arduino boards… just in case the one you used became damaged. Maybe it’s not damaged… but ----- just in case.

RaceEngineer:
Yes haha but I didn't do this??! Please READ...

When typing.... please convey the full thing. That is, when you typed ---- 'I didn't do this'.....just type something like 'yes, I applied more than 5V to an analog pin of the arduino'...... or 'no, the input analog voltage never exceeded 5V'. Just need to be clear about what you're trying to say.

Anyway, if you have a circuit diagram, plus photos, and if you mention that you believe that you never exceeded 5V for an analog input, then that will be good.

Also.... to be clear....whenever mentioning 'measured the voltage'.... indicating how you measured it.... such as with multimeter.... or with arduino analog to digital conversion etc.

Hi,

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

A picture is worth a thousand misunderstood words..

Tom.. :slight_smile:

I conclude the OP has burned a spot on the resistance track in the pot. Gee, I have never done that!

Paul