I was wondering if someone can illuminate the impact of a headphone output's impedance, but more importantly if my assumption is correct that my question actually pertains to impedance!
I have been using a circuit which worked great... until with another audio source (ie computer, ie soundcard) it stopped working as it did before and I was left scratching my head why. As you can see with the circuit below:
- 2 100k resistors mix down left/right channels to mono
- a 100k pullup resistor
- a Schottky diode to prevent negative voltages coming to the Arduino digital input
The reasoning here is that if the audio jack isn't connected (ie supplying a low voltage audio signal) my digital pin will detect the 5V pullup and therefore be able to determine that my audio jack isn't connected to anything. This worked great until I needed to apply this circuit to a different motherboard and I saw that the pullup was in fact actively biasing the input upwards resulting in my digital input pin detecting HIGH while in fact the audio signal was active.
Initially my pullup was 10k. Then on another motherboard I started noticing the biasing, which was prevented by increasing it to 100k. However on the motherboard I'm working with now, even the slightest pullup biases the signal upwards.
It leads me to question what it is about difference audio sources (audio boards) which exhibits this variation in outcomes. Can anyone explain what's going on? Is my unfounded hunch of impedance anywhere near true? I'd love to know.
And eh... if you have a killer tip about detecting when an audio jack is connected or not I'd love to know too, but the above is my main question