Help with pot - linear vs audio

[ironsider]

Hi,

I've received a load of these slide potentiometers from here: https://www.mouser.co.uk/ProductDeta...pI22NVZw%3D%3D

As you can see on the link, these are linear potentiometers. However, when I read them with the Teensy's ADC I get what look very like audio/log values.

Can someone give me a sanity check here, as I'm really confused how this could be the case - I've checked this model on some other major suppliers website and it's also listed as linear. Is it possible that some sort of wiring issue could cause some sort of non-linearality with a linear pot (I'm thinking no, or at least not without the output being essentially noise)?

Here is the code I'm testing with: very vanilla (just a built in Arduino IDE example:

// These constants won't change. They're used to give names to the pins used:
const int analogInPin = A0; // Analog input pin that the potentiometer is attached to
const int analogOutPin = 9; // Analog output pin that the LED is attached to

int sensorValue = 0; // value read from the pot
int outputValue = 0; // value output to the PWM (analog out)

void setup() {
// initialize serial communications at 9600 bps:
Serial.begin(9600);
}

void loop() {
// read the analog in value:
sensorValue = analogRead(analogInPin);
// map it to the range of the analog out:
outputValue = map(sensorValue, 0, 1023, 0, 255);
// change the analog out value:
analogWrite(analogOutPin, outputValue);

// print the results to the Serial Monitor:
Serial.print("sensor = ");
Serial.print(sensorValue);
Serial.print("\t output = ");
Serial.println(outputValue);

// wait 2 milliseconds before the next loop for the analog-to-digital
// converter to settle after the last reading:
delay(2);
}

[PaulS]

This fader comes in 2 resistance taper flavors: with audio taper or with linear taper. See this table:



If it is really a linear fader, you should read a sensorValue of ~0 at one end, ~1023 at the other end and ~512 in the middle.
The Mouser link refers to: PTB0153-2010BPB103. That should be a 10K linear taper. Do you see that part# somewhere on the housing?

Paul

PS: how did you wire this fader to the Teensy?

[MarkT]

Check the pinout. Fader pinouts are not intuitive, you need to check them.

[PaulS]

Ran your code on a home-made MIDI-controller with 100mm linear ALPS faders [exact same pinout as your Bourns faders].
The sensorValue values look very linear in relation to the position of the faderknob.
Fader pin 1 connected to Teensy GND, fader pin 2 connected to Teensy pin A0(14), fader pin 3 connected to Teensy pin 3V3.



Paul

[SmashedTransistors]

Don't forget to disable the digital input hysteresis.


https://forum.pjrc.com/threads/69671...-Analog-Inputs

[PaulS]

Don't forget to disable the digital input hysteresis

Good suggestion when using a Teensy 4.x.
In my quick test above, a Teensy LC was used so this is not applicable.
But not knowing which Teensy the OP used, it might be useful. Although I doubt in his case this solves his issues seen.

Paul