potentiometer on the STM32F746G

[dennis]

Posted on June 16, 2016 at 16:45

I was hoping to wire an external potentiometer to the ADC on the STM32F746G but even bypassing the input cap (C107) I still seem to get AC readings.  E.g. I bump the pot one way and I get a positive blip, I bump it the other I get a negative blip.

I read stuff suggesting previous STM32 boards had an onboard pot but unless I'm missing something really obvious in the manual I don't see a pot on the 746G.  Is that correct? Any ideas how to get a multi-valued DC control signal into the board? Again, I did a brief search here but the site is so slow it tends to discourage much searching. #analog-input #lacks-specificity

[LMI2]

Posted on June 16, 2016 at 19:56

Forum SW sucks.

I have several several Discovery boards and none have potentiometers. Some cards have jumpers on the bottom, are you sure you have really connected your pot to the CPU. I have STM32F746G too. I looked at it with the Cube and I could not find any free pins, could it be that the CPU is using your ADC pins for something else.

[AvaTar]

Posted on June 16, 2016 at 20:13

> I read stuff suggesting previous STM32 boards had an onboard pot ...

I think some evaluation boards (not the cheap ''Discovery'' board) have potentiometers. I rarely had issues with potentiometers on the ADC, in F100, F050, F303 and F407 discovery boards. Just keep the wiring short, and the potentiometer resistance low (max. 10k). And with having a multiple of 50/60Hz as sampling frequency, you can subtract out effects of mains AC.

[Tesla DeLorean]

Posted on June 16, 2016 at 21:15

What board? How exactly is the pot wired up, etc...

What's the software look like, and what readings, specifically, are we seeing from said code?On the newer DISCO boards the Arduino Shield socket should provide ready access to a number of Analog Pins, see also NUCLEO boards.

[dennis]

Posted on June 17, 2016 at 20:03

I used one side of the ADC as I was assuming an analog input needed to go thru the ADC.  I soldered around C107 (I think, hands were a little shaky and that's a teeny little cap) but my readings were still like there was a DC blocking cap.

Just figured getting a control signal into the board was probably a pretty common problem...

[Tesla DeLorean]

Posted on June 17, 2016 at 21:58

Ok, so assuming the STM32F746G-DISCO board, but it is important to impart detail when framing a question. The STM32F746 is a chip.

C107 is on the Mic Jack and connected to the Audio Codec, it is *NOT* connected the F7 ADC inputs. Consider using one on the Arduino connector, see

http://www.st.com/content/ccc/resource/technical/document/user_manual/f0/14/c1/b9/95/6d/40/4d/DM00190424.pdf/files/DM00190424.pdf/jcr:content/translations/en.DM00190424.pdf

[dennis]

Posted on June 19, 2016 at 04:35

Ah ha.  #1. Didn't realize STM32F746G needed ''DISCO'' to be specific.  Got it.

#2. I didn't see the other ADCs.  I was just focused on the WM8994. Thanks.  -- Dennis