Audio Port to Detect Contact Closure

I need to detect the contacts of a hardware push-button, using the audio port.

I plan to use a LOOP-BACK Circuit where the push-button contacts make/break the connection to the mic input.

The idea is that when looking for a push-button closure I would output an audio signal and detect if the signal was being looped-back to the mic. If present, the contact would be closed.

What is the easiest way to achieve this in B4A?...

Audio Port to Detect Contact Closure

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