I'm trying to read the audio signal of a 3.5 mm audio jack (headphone cable) on my arduino uno. I followed some tutorials, but the amplitude of the signal is so low (hardly above 0 volts, so i guess the original signal amplitude).
can anybody help me on how to get the amplitude to 0 to 5 volts?
Audio is AC, so you only want to amplify it to +- 2.5 volts and apply a DC bias of 2.5 volts before connecting to an Arduino AD pin. What is your project?
Use the 1.1V ADC internal reference and you won't have to amplify it.
https://www.arduino.cc/reference/en/language/functions/analog-io/analogreference/
By the way, please post a real schematic.
Headphone, or line output cables typically have a signal level on the order of 1 VAC peak to peak (when the volume is turned up appropriately).
You need to offset that signal with a voltage divider, and make sure that any inherent DC offset is removed.
It appears from the photo that this is what you tried, but there is NO CONNECTION shown from the 10K/10K voltage divider to the audio input. The gap in the protoboard is an insulator.
Example schematic:
Thank you all for your replies, much appreciated.
I am trying to make a sound reactive VU like this: Stereo Vu meter - second edition - YouTube
Jremingtons's schematic is correct, that is what i need. I'm still having trouble trying to get convert the schematic to the breadboard. Is this correct?
The audio signal (+) goes into 24, then into the - pole on a 10 µf capacitor. the + pole of the capacitor goes to 23 on the breadboard. Then there are the two 10k resistors and finally the signal to my arduino.
The signal is oscillating around 2.5 volts, so far so good. It is however still not amplified. Can somebody please point out my mistake?
There is nothing to amplify the signal. Your circuit just adds a voltage offset.
Since you use an electrolytic cap you need to have audio on the negative pole. From your pic I cannot see if it is OK this way.
If you want amplification you could use a transistor or an opamp
With the volume turned-up you should be getting "usable" readings from a headphone output or a line-level output but you probably won't get the full 5V range.
With the 2.5V bias circuit you can't use the 1.1V reference but here is a circuit that kills the negative half of the signal so you CAN use the lower reference and get about 5 times as much sensitivity (similar to 5X amplification).
With the 1.1V reference, each ADC count is about 1mV and that should help. Note that half of the readings (the negative half of the waveform) will be zero.
For a VU meter it's OK to ignore the negative half of the waveform but if you want to do any frequency analysis it won't work properly,
...You can make an amplifier with an op-amp but that shouldn't be necessary.
As ignored in post #3. You only need to change the bias network values to provide 0.5V DC offset.
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