circuit to detect a beep

[Fido]

I have a raspberry pi that has a gps attached and I can record a coordinate.

My metal detector has an earphone socket. I want to connect this socket to a circuit that sets an rpi GPIO pin high when a 'beeb' is produced and then sets it low again.

The logging bit on the rpi I can do, but does anyone have the electronics knowledge to suggest or give some hint on a circuit design to do this.

Thanks

[Skippy]

You will probably need to apply a dummy load to the headphone output, to simulate the headphones, try 100 Ohms as a starting point.

To detect the presence of an AC signal, one simple way is to use a voltage-doubling rectifier, see here:

https://www.allaboutcircuits.com/tex...e-multipliers/

[Fido]

Thanks Skippy, that looks like just the starter hint I was after.

[moodz]

...read this ��
https://learn.adafruit.com/fft-fun-w...rms/tone-input

[Skippy]

If you're wanting to detect a specific frequency tone, then phase-locked loop based circuits are worth considering. One obvious choice is the NE567 ( SE567, LM567 ) IC, designed specifically for this purpose. But you could probably use other PLL chips to achieve the same results, eg. the CD4046 and its variants. And there's also the BA1604.