I have to interface a radio (for emergency alerts) to a POTS telephone jack.
When the radio squelch opens, it needs to take the phone "off hook" and send the sound into the phone line, then disconnect when the radio goes quiet.
I built this circuit and it is working great. It does have a small issue with picking up noise from the building power line and false tripping, but it is rare.
I would appreciate any critiques. Especially on my false tripping problem.
http://dl.dropbox.com/u/18786384/alert.png
Speaker level audio comes in to the audio jack, and the phone line connects to J3. The xformer is a standard 600 ohm telephone transformer.
Thanks.
When the radio squelch opens, it needs to take the phone "off hook" and send the sound into the phone line, then disconnect when the radio goes quiet.
I built this circuit and it is working great. It does have a small issue with picking up noise from the building power line and false tripping, but it is rare.
I would appreciate any critiques. Especially on my false tripping problem.
http://dl.dropbox.com/u/18786384/alert.png
Speaker level audio comes in to the audio jack, and the phone line connects to J3. The xformer is a standard 600 ohm telephone transformer.
Thanks.