Detecting tones from PC audio output

[chipco3434]

This is w*rk related. I will apologize in advance!

I want to detect the presence of a ~1 second tone coming from the audio output jack of a PC. I don't need to hear the tone, just detect it's presence and control a relay. Clearly, I can record any tone and assign it to the application interface.

From the top down, RCA into the output jack, into a magic box to detect the signal and then control a relay. This is important because it provides the income for this crack addict hobby!

(If you are interested, this is to detect failure of statistical control and capability in a real time manufacturing process. We will use the signal to interrupt the operation.)

[pinkmouse]

Make it fail safe instead

Buffer for input, rectify and smooth signal, Schmidt trigger, and transistor to drive relay. Then the process will interrupt as soon as the signal disappears, and start when the signal does. Job done.