[Project Suggestion] Input jack state detectable through GPIO

[roryjamesallen]

Input jack state detectable through GPIO

Describe your suggestion or idea
Allow the state (whether a cable is plugged in or not) of any input jack to be checked through software to allow default values to be set if not patched, or for example to allow an external clock to replace an internal one, and then immediately switch back upon removal of the patch cable.

[roryjamesallen]

Suggested implementation

This seems to work in falstad although testing on a breadboard is still required.

• When no cable is connected, INPUT_STATE_GPIO is connected to INPUT_GPIO via the Thonkiconn switched pin, which is in turn pulled to ground by the 1k resistor
• When a cable is plugged in, the connection between INPUT_STATE_GPIO and INPUT_GPIO is broken, and INPUT_STATE_GPIO is then pulled high by the 100k resistor
• The diode prevents the GPIO from being exposed to the input voltage as it will be connected for a brief period before the switched pin flips (further testing required to check behaviour with negative input voltages, potentially a diode clamp to ground will also be needed)
• Whether or not a cable is connected can be observed using the value of INPUT_STATE_GPIO as a boolean, with 0 being nothing connected and 1 being connected
• This value can be used either with the polling (checking the value) method, or the likely more useful interrupt method, where the plugging in or out of a cable triggers a software interrupt to perform a relevant function

Any input conditioning, for example a transistor for a digital input or op-amps for an analogue input, will come after this whole stage, directly before INPUT_GPIO in the diagram.