Reading from mono jack

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1

Hello everybody.
I am an absolute beginner in Arduino, and this is one of the absolute first projects I do with it.
I am trying to read the voltage from a mono 3.5mm Jack cable. I am following this schematic which I found in an other post. https://forum.arduino.cc/t/how-to-read-data-from-audio-jack/458301/3
I will say that I am not using the capacitor between audio input and pin A0 and the resistor between Audio ground and audio input.
All I can receive from the serial monitor is a constant value of 509.
I have been trying to do it all day! I would be extremely grateful for any help.

1 Like
2

Welcome to the forum

So are you following the schematic or not ?

3

Please follow the forum rules and post the code, using code tags. See the "How to get the best out of this forum" post for instructions.

4

And I assume you also don't have R1?

With R1 and no capacitor and nothing connected to the audio jack, you should read around 100.

Without R1 or the capacitor, and no audio connection the "expected value" with perfect resistors is 511 or 512 (half of 1023).

So 509 is fine, and if you are reading that with the audio connection, it should be OK with this particular connection. But with a different audio device you may not be so lucky.

If the value is constant you're not getting any audio signal or the audio signal is too weak. Is it a line-level or audio signal?

...It's unlikely to pick-up anything from a microphone (a few millivolts) and electret condenser computer mics need power.

5

Thank you very much. The 3.5mm jack is connected to two ecg pads. I am trying to detect the fluctuations in electricity that can happen in a human body or in a plant.
Would adding R1 and the capacitor allow me to detect these? Or would I need to somehow amplify the signal in the jack?
Or perhaps this circuit is simply too simple to detect signal from ecg pads?
Thank you again for your answer

6

Both. You will most certainly need to amplify the signal.
See this:

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