In the hope of using the standard 3.5mm audio output found in your average PC/smartphone to control (not power) a DC motor, I was measuring the voltage between GND and Tip and noticed the following:
- When no audio is playing, there's a voltage of about 2 mV.
- When I output a constant audio signal, the voltage rises initially to 0.5 V, but drops back to 2 mV after 2-3 seconds.
What purpose does this 2 mV bias voltage serve? Does audio output circuitry usually contain DC blocking capacitors, or is DC blocked via some other means?