01-29-2021, 02:37 AM
Is there DC bias in the audio output? Should be easy enough to measure.
I don't think there needs to be anything wrong with the circuit. It could be the pin for the RC3399 GPIO is configured with an internal pullup. It would be in the pinmux section in the dts. In this case, when the headphones are inserted, the HP_DET_H line is disconnected from HPO_L and isn't driven by anything other than the internal pullup. The only connection appears to be a 100 nF cap on the small board. So the level rises to a logic 1. The cap would help to debounce that.
When the headphones are removed, it will be driven to the level of HPO_L. And that should be low enough to be detected as a logic 0.
Since there isn't really a debounce circuit, there's might be multiple interrupts triggered per insert/removal. But that doesn't really matter. Just debounce in software by ignoring interrupts for a bit after the first one.
I suppose a continuous high level on HPO_L could be enough to trigger the circuit.
And yes, if they had just added a rs232-usb chip we could have a serial console, and headphones, and no analog switch, and no need to open the pbp to enable the console, and no special console cable that's over the voltage limit.
I don't think there needs to be anything wrong with the circuit. It could be the pin for the RC3399 GPIO is configured with an internal pullup. It would be in the pinmux section in the dts. In this case, when the headphones are inserted, the HP_DET_H line is disconnected from HPO_L and isn't driven by anything other than the internal pullup. The only connection appears to be a 100 nF cap on the small board. So the level rises to a logic 1. The cap would help to debounce that.
When the headphones are removed, it will be driven to the level of HPO_L. And that should be low enough to be detected as a logic 0.
Since there isn't really a debounce circuit, there's might be multiple interrupts triggered per insert/removal. But that doesn't really matter. Just debounce in software by ignoring interrupts for a bit after the first one.
I suppose a continuous high level on HPO_L could be enough to trigger the circuit.
And yes, if they had just added a rs232-usb chip we could have a serial console, and headphones, and no analog switch, and no need to open the pbp to enable the console, and no special console cable that's over the voltage limit.