I don't understand this. This photo seems to be different from the first.
Are you still getting the changes without you touching anything?
Ok so here is the result i get now :
no sounds :
pot low :
pot high :
Bt what i'm afraid of is that i have the same results from the plotter when the pot is disconnected from the audio source (speaker left pin of the mp3 module)
Please post a schematic so this guesswork game doesn't run into hundreds of posts. If for no reason, other than that you have multiple power supplies...
Also, you didn't acknowledge the possible issues mentioned in reply #37. You need to check your grounds.
The wiring on the proto board is an untidy mess. When you bunch wires together in close proximity like that, there is a good chance of a bad connection or short. Plug the components in and run jumper wires as needed, don't cluster the connections.
Example, place the resistors so they are flat on the board, sharing one connector row. Use jumpers to connect this divider circuit to the rest of the circuit. Some component leads are oversized for the proto board sockets. If you have any of those, you should solder smaller wires to them, or use a different part.
That suggests that the speaker is not delivering the signal you require.
Have you tried the right speaker pin?
It could be that the sound module has a class D amplifier
Class-D amplifier
And so requires the inductance of the speaker to actually make it work.
Did you ever supply a link to that board? Can you read the numbers on its two chips?
This is a time to use "divide and conquer" methodology. You don't really know whether the source or the input is at fault, or possibly even the match between them. That's because you have no certainty about either. You have to either connect a known good audio source to the input, or connect the source (module audio output) to a known good input that can help analyze it, like a scope or DAW.
Also, you are ignoring my repeated requests for a schematic. That makes it difficult to evaluate the interface. The pictures were only partially helpful, because they don't show the connections clearly and also demand an unreasonable amount of time to trace everything visually.
By not following the forum guidelines, you are "shooting yourself in the foot" because there may be a really simple cause which we could see instantly if you would only provide the details.
Given that your target is just a simple envelope follower and threshold detection, the input shown with "pot high" would probably suffice for further software decoding. It looks relatively clean. You could probably omit the pot entirely, or substitute a fixed resistor.
It does appear to have an incorrect offset, varying between mid and full scale instead of being centered around the middle where it should be. The discussion of why that is the case rests on the hardware you haven't shown.
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