Attention: Nate

I've been thinking about how to do things for that project.

The Baofeng UV5R is cheap, can transmit 4W on two meters, and has a green LED that lights up when it breaks squelch.

From what I can find, the Raspberry Pi has an audio output, but no audio input.

So I propose to take the processor pin that drives that LED (The processor is 3.3V), disconnect the audio from the speaker-out jack, and put the squelch signal on that connector.  Then that can go to a 3.3V GPIO pin on the Raspberry Pi, and you can decode keying from that.

Since it's driven by the processor, should we decide to protect it with a CTCSS tone, that's just a setting in the radio.

There's a microphone input, which I think expects electret mic inputs of ~10 mV, so we'll have to pad the output audio from the RP down quite a bit, I imagine.  Do you happen to know what the output voltage on the RP audio is? I'd expect somewhere in the range of .7V to a volt.

You'll need to have another GPIO to key the transmitter, and we may want a relay or optoisolator between the RP and the radio.

I'll have to find the schematic and look at it, but I think it keys up when you ground the PTT line.

The radio comes with a funky little microphone/earpiece, so that gives us the connector to plug into the radio.

It comes with a charger that stands the radio up and can charge the battery while it's operating. It's powered by a wall wart

Anyway, that should be pretty simple, and do the job without going through a USB sound card, which is just another thing to go wrong.  We don't really need RX audio, just the squelch signal.

Somewhere around here, I've got a serial cable to allow programming a Baofeng via computer, but it seems to have evaporated.

Good that you've identified a radio with GPIO support. I was considering just pulling apart a speaker mike and reed switching the PTT, and possibly matching up my own "line IN" but your solution specified here is cleaner.

Agree that all we need is the squelch since we are only looking for "clicks" in a regular succession.

I don't know the output voltage of RP audio, but its an easy thing to check. Audio input can be gathered with an external (USB) sound card. Looks like you've worked around that however.

My email is (remove three pound # signs).

Thanks for the detail and insight on this; appreciate your help.