# Digital Potentiometers Always Read Half of Full Scale

I have a PR60-21_50K that I’ve been experimenting with in our lab as a means of simulating NTC temperature sensors. I am able to connect to the board using NCD Base software without issue. I am also able to change the resistance of all the potentiometers within the software, but when I measure the resistance values using an ohm meter, they always read about half of the full scale value (about 25 k-ohm). I know the software works because at one point I was able to change the resistance values within the software and then verify the change with an ohm meter. I was also able to change the power-up default values. I know the power-up default values are all set to full scale, but still on power up the value I read with my ohm meter is half of full scale.

Any idea what could be happening here? Nothing I can think of except maybe the MCP42050 chips were damaged somehow without my noticing.

Hi,

One thing to keep in mind is the maximum voltage that can be passed through the digital potentiometers is 5VDC. The maximum current which can be drawn through the digital potentiometers is 1mA. If either of these limits were exceeded it could damage the digital potentiometer.

Can you provide photos of how you are connecting to the digital potentiometers to measure resistance(show ohm meter connected to screw terminals).

Thank you,
Travis Elliott

Sure, I am connecting from An to Wn, where n is the channel. For example, to measure channel 0, I connect the ohm meter probes as shown in the attached picture.

As I said, this was working at some point, so not sure what happened. The maximum voltage that my circuit can apply to a single channel is 2.63 V, so it is possible that a small enough resistance value could draw more than 1 mA. But this is why I configured the power-up default values to be the largest possible resistance value, and I made sure to keep the resistance above 5 k-ohm just to be safe. Also, only channels 0 and 1 have been used in my circuit, but all channels (channels 0-7) are stuck at half of full scale.

In the event that I did damage the MCP42050 chips, I have ordered 4 replacements that should arrive later this week. I will try to swap the new chips in when they arrive.

Let me know what you find out after swapping the pots. If that does not work we will do an RMA so we can take a look at it.

Thank you,
Travis

Swapped all the pots out and now the board is working as expected. Guess this was my bad. Thanks for the help.

Thank you for the update. Please let us know if you need anything else.