Going crazy over simple slide potentiometer

I have purchased a motorized slide potentiometer from Bourns. I'm just trying to get a basic reading of it in a voltage divider setup before even connecting the motor, and despite scouring the data sheet (which isn't much, this thing is simple!) but for the life of me, I can't figure out what's going on. I assume I must be misunderstanding the part.

The part is: PSL01-1082A-103B1 PSL Series Motorized Master Slide Potentiometer
Here's the data sheet: https://www.mouser.com/datasheet/2/54/psl-1280324.pdf

If I am understanding correctly, this is a linear taper potentiometer. I cannot get stable or consistent results from the potentiometer track on either of the identical parts I purchased.

When I try to read the resistance across pins 1 and 3 of the 4 pin pot connector, I am expecting a stable constant resistance. I get wildly varying values on my Fluke multimeter that reads other pots fine. I get values around 116Kohms, but the value jumps around even if I just set the pot down on the table with the multi test leads attached.

When I try to read the resistance across pins 1 and 2 (the wiper) I get incredible noisy readings, ranging from about 30ohms on one side of the slide pot level position to 13K ohms on the other. If I push the slide level with even minor force towards the extreme ends of the pot, that reading shoots up to ~130kOhms.

When I connect the pot to an Arduino UNO, with pin 1 to +5V, pin 2 to A0, and pin 3 to GND, and try to print the value with the default AnalogReadSerial example, I get extremely, extremely noisy values that jump around and often make no sense. I get this same behavior on both of the versions of this part I purchased.

Just to be clear, and I aware that one of the four pins is the touch track, and I am not accidentally testing that.

Perhaps I'm fundamentally misunderstanding the part, but I've scoured the data sheet and it doesn't seem like I'm missing anything. I assume I'm supposed to be able to read this like a standard slide pot so I can use that value to drive the motor. I purchased another Bourns motorized slide pot, a PSM01-082A-103B3, and its potentiometer (both tracks) works exactly as expected, with stable readings on my multimeter and microcontroller. However, this part will not work for my application due to its size.

Any idea what might be going on here? I'm losing it

Do you know there are two pots in this device, one is for passing audio through and the other is used for the motor position feedback.
They are differentiated by the’ next to the pin number, so you have 1 and 1’, 2 and 2’, and 3 and 3’. So you must always use either all the ‘ pins or all the non ‘ pins when making measurements.

Sorry if you know this but you don’t mention it.
The other thing is that you should use a proper connector and solder it in, I have found sometimes the hard Crome plating on the probes do not make the best contact.
I have used that part and initially I was getting the connections wrong.

Hi,
From the datasheet.


Tom.... :slight_smile:

If it helps this was my schematic for four motorised sliders. There were end firing LEDs along the track you can see them change colour at the slider position. I used an ATtiny85 to communicate with the LEDs so that the strip update time did not clash with the motor control and I2C slave system interrupts giving the pot position. It was a module of a much larger system.

Hi guys,

Thanks for your replies. Unfortunately, I wish this was the mistake I'm making. If you look more closely at the part number I listed, you'll see I am using a part that has only a single potentiometer track, ie "R1 Track" in the data sheet. This particular part number has dimensions that work better for my project. I have made this image to show you how my part number corresponds to which features according to the data sheet, so you can see that I only have one track.

PSL01-1082A-103B1

Given this, please note that my post above, when talking about pins 1,2, and 3 (and never T) is referring to the 4 pin "Configuration 1" A Connector from page 2 of the data sheet.

So, this is why I am surprised I'm not getting 10Kohms when measuring with a multi across pins 1 and 3. It's also why I flat out have no idea of why when I connect pin 1 to 5V, 3 to GND (on an Arduino UNO) and 2 to A0, with the default AnalogReadSerial example, I get wildly noisy values. I have tried several Arduinos. Also, to your point about the probes Mike, I have two of this part. I actually got mad and trimmed the casing off the connector of one of them and directly soldered on male/male jumper wires, so I could see if somehow my JST connector was bad:

Still, same wacky readings (on both copies of the part) when reading across 1/3, and when hooking 1 to 5V, 3 to GND, and 2 to A0.

I was getting such weird values with the first version of this part that I ordered the other one expecting the pot on the first one was bad. When I got the second one in the mail and it behaved the same way, I started thinking I must be misunderstanding something about the potentiometer. But I've stared at the data sheet and it doesn't seem like this is rocket science. I have no idea what I'm doing wrong.

Hi,

When I try to read the resistance across pins 1 and 2 (the wiper) I get incredible noisy readings, ranging from about 30ohms on one side of the slide pot level position to 13K ohms on the other. If I push the slide level with even minor force towards the extreme ends of the pot, that reading shoots up to ~130kOhms.

Do both slide pots show this characteristic?
What do you get between 1 and 3? (Both pots)
What do you get between 2 and 3 as you slide? (Both pots)

If 1 and 3 is much greater than 10K, then the track is probably cooked.

Tom..... :slight_smile:

It is easy to fry a pot by connecting 5V and ground to the wiper and one end.

No idea if this is relevent or not but I was getting weird reading on A0 when trying to read voltage divider values. Originally I was using an ATMega328 and all was good but then I transferred the program (with amendments) to an ATTiny3217 and it stopped working. I found that I had to add this line:

pinMode (A0, INPUT)

Now works great.

windoze_killa:
No idea if this is relevent or not but I was getting weird reading on A0 when trying to read voltage divider values. Originally I was using an ATMega328 and all was good but then I transferred the program (with amendments) to an ATTiny3217 and it stopped working. I found that I had to add this line:

pinMode (A0, INPUT)

Now works great.

Thanks for that, as you have found, 328 doesn't need to have a pinMode statement when you us AnalogRead.
Its good to know that the you need to us it for 3217.
Thanks.. Tom.. :slight_smile:

TomGeorge:
Thanks for that, as you have found, 328 doesn't need to have a pinMode statement when you us AnalogRead.
Its good to know that the you need to us it for 3217.
Thanks.. Tom.. :slight_smile:

I am not sure that it does need it as one of my projects works without it but the other didn't.

One possible explanation is that it powered up with the internal pull up resistors being set and that command effectively disabled them.

I've written to Bourns who make the part, and they wrote back that they think there might be something wrong with the samples. I think they are going to have me send them in to them to analyze.

I don't think I blew the pot since I was very careful about what pin I plugged into GND/PWR/A0 on the very first try, and, the ground/pwr I was plugging into was just Arduino 5V/GND over my Mac USB so I can't imagine 500mA frying it. As for the question about A0 configuration, I'm able to read A0 no problem with other motorized pots I have here, so I'm just really suspicious of this dang part.

I'll update this thread once I get anywhere with Bourns. Thank you all for your time and help - even if it feels like we didn't get to the bottom of it just now, all of you helping me gut check whether I was making an obvious error was very helpful in deciding to write the manufacturer, etc.

More later!