Potentiometers reaching max value early on ADAU1701
Thread Summary
The user encountered potentiometers reaching their maximum value (0.999...) prematurely on a Dayton KABD-430 board while programming with SigmaStudio. The solution involves adding a 100 ohm resistor in series with the potentiometer to limit the voltage to the AUXADC input to around 3.0V, as the typical full-scale input is 3.0V, and the potentiometer is powered by 3.3V. This adjustment will help protect against cable shorts and ensure proper potentiometer operation.AI Generated Content
Hi,
I have a Dayton KABD-430 board that I'm programming using SigmaStudio. I also have the potentiometers from the cable set they provide (1k ohm linear). The potentiometers reach their maximum value (0.999...) early, they can still be turned about 10-20% of their range physically. I've tried different pots (other manufacturer, same rating), same thing. I have a readback cell right after the ADC in, so no processing is being done. I have the same problem when indexing a lookup table, I hit the final entry early. Is this a known problem and how do I fix it? Thanks in advance!
Kind regards,
Julian
Audio Signal Processors
hardware
SigmaDSP Audio Processors
adau1701
Hello Jullian,
Well, this is a little of a combination of factors.
The first is that all pots usually have a short bit of turn that has no change near the end. They do that to make sure both ends of the pot can be reached and account for mechanical tolerances. But not quite as much as you describe.
So the next factor is the AUXADC input specifications itself:
The typical full-scale input is 3.0V. I assume you are using 3.3V at the top of the pot. I do not have the schematics for that board. I do have one here in my office but this spec is part of what you are seeing. The best way to deal with this is to have a resistor in series with the top of the pot. So that the voltage at the top of the pot will be around 3.0V. You could even get fancy and put a pot at the top of the pot so you can dial in the max. But that is a bit crazy.
So I took out my pencil and calculator and figured out that a 100 ohm resistor in series should do it.
Here is a pic of my calculation:
It is probably a good idea anyway to protect against a short in the cable.
Dave T
Hi Dave,
Thank you for your excellent reply! A bit annoying that the board doesn’t account for this as it should be an all-in-one solution, I’ll let Dayton know! A resistor it is.
Regards,
Julian
Please log in to reply.