Issue with GPIO Analog In/Out Pins

#1

First, let me say that I accept this very well maybe a hardware issue of my own creation, but before I start tearing things apart:

I have both gpio pins (PA4 and PA5) wired to stereo 1/4" jacks. They are wired: gpio to tip, 3.3v to ring, and ground to sleeve. Power and ground are wired in series with 8 other pots I have connected. Here's the results I get:

Expression pedal into PA4: Pedal controls a disp/dial p with almost the full range from 0-64, but also afftects a dial connected to PA5
Expression pedal into PA5:Pedal controls a disp/dial p with almost the full range from 0-64, no affect on PA4

I have a pedal with an expression in, designed to take 3.3v, and wired per TRS the connections I note above.

PA5 works to send control signals to the pedal, which reacts as expected, except I have to phyically disconnect the wires from the board to PA4. If PA4 is also wired up, it kills the pedal when plugged in.

PA4 kills the pedal when plugged in, even if PA5 is unhooked.

I talked to the guy who made the pedal and from the pedal being "dead" he guesses that the expression is somehow shorting power to ground. Unplug the expression jack from Axo and it works normally again.

Like I said -- it's very possible I have a solder bridge somewhere, but when I load the gpio/analog/out object I see both PA4 and PA5 which makes me assume they share a bus internally on the board and this could be related.

Ideas? THANKS!!

#2

Oh yes, 2 more details:

Per @johannes recommendation, I have a small resistor in series with the 3.3v in order to prevent the board crashing when plugging/unplugging a jack.

I have also used my multimeter to test for continuity between the pins and jacks and found none.

#3

I assume your pedals are akin to pots, right, like an EV-5.
So, what happens when you test with 2 pots instead of your 2 pedals? Same thing?

#4

Also, you're using VDDA as 3.3V, right?

#5

Pedal is a M-Audio expression pedal, which is a 10k linear pot wired to a TRS jack, so same difference. Appreciate the ideas though, so if I am misunderstanding I am happy to test whatever to see if I can figure this out.

Yes, VDDA for analogs.

#6

What do you mean by "Power and ground are wired in series with 8 other pots I have connected" ?
This does not sound right...
Do you have a picture of your connections ?
:thinking:

#7

Connected to the board and then run to each pot and these 1/4” jacks. So same VDDA is connected to each one, and also same ground.

Here’s a picture to illustrate:

F2CC46A4-8012-4154-92AC-4C0FD2A4AD26.jpeg636x623 360 KB

No issues with the pots at all.

#8

Those connections are parallel connections, when you said series, my first thought was the connections. But all seems fine there.
I think you need to focus on the PA4 and PA5 pins. I know various expression pedals have different TRS connections, one of my pedals actually lets you choose between 2 configurations.
If you are getting display dial movement on both PA4 and PA5, it is because when plugged into the pedal, somehow voltage is getting to the PA5 pin.
Somehow also I think your comment "with almost the full range from 0-64" is also important, because you should be getting full range.
What I recommend, get your multimeter, plug in your pedal to PA4, and from here check the connection of the 3.3v power line to you PA5 connection, Ground to PA5 connection, the PA4 to PA5 connection. Somewhere one of these should connect through when it shouldn't. Could be a bad solder, malfunctioning TRS jack, faulty expression pedal.
The other thing you could do is, connect your TRS to a pot, because expression pedals are usually just turning a pot, so this will tell you if it is a problem with the expression pedal.
:grinning:

#9

Duh - you're right. Parallel! Thank you, good info and I will look into it!

Do you think the expression in is related to the issue I have sending the analog out signal? That's where the main problem is.

#10

You would have to test it to see, PA4 and PA5 work with a standard pot wired on, then its either the expression pedal or a fault in the TRS jack.
If its the Expression pedal, may not be broken, may just by wired on the jack wreong for that pedal.
:grinning:

#11

Do you use PA5 to receive info from the pedal (PA5 with an object gpio/in/analog), or do you send info from your axoloti to the pedal (it's what I read from your post).
A pin from the GPIO can only work in one given mode: either it's an analog input, or a digital output (or a digital in...)

#12

The issue you quoted occurs when sending out with the connections as noted. I have also tested in with an expression pedal in to see if I get expected behavior. Only doing one at a time, not trying to do them both in a single patch. :slight_smile: