At my home, we have a PBX driving a number of Linksys SPA942 phones. As they can operate as remote hands free intercoms if the number is dialed with an "8" in front, I had a thought it could be fun to drive my HF radio that lives in the shed from the comfort of my house.
So far, some tests look promising.
The target phone has a Selectone ST-139 CTCSS Encoder/Decoder grown into it to detect the CTCSS produced remotely to operate the PTT.
For the test, I needed to find a point where the phone's received audio could be tapped. After looking at the data sheet for the WM8750 chip, here is the spot. I removed C128 with the idea of removing the CTCSS tone from the audio stream, and the Selectone board may be doing that, I think.
The Selectone board is set up for 127Hz, and the output drives a relay with an LED across it,
When the phone receives the correct CTCSS tone, the Selectone board operates the relay.
and the LED lights on the front to indicate TX.
At the moment, one of my Arduino boards is generating the CTCSS, and is fed a transformer that is resonated at the tone freq. This is a transistor radio speaker transformer and the secondary is in series with the mic that is plugged into the headset connector of the "house" phone.
Eventually, the CTCSS generator and a PTT button will be installed inside the house phone so it can be used as a handset, headset or speaker phone.
When I get it working, I'll post full details.
Watch this space!
So far, some tests look promising.
The target phone has a Selectone ST-139 CTCSS Encoder/Decoder grown into it to detect the CTCSS produced remotely to operate the PTT.
For the test, I needed to find a point where the phone's received audio could be tapped. After looking at the data sheet for the WM8750 chip, here is the spot. I removed C128 with the idea of removing the CTCSS tone from the audio stream, and the Selectone board may be doing that, I think.
The Selectone board is set up for 127Hz, and the output drives a relay with an LED across it,
When the phone receives the correct CTCSS tone, the Selectone board operates the relay.
and the LED lights on the front to indicate TX.
At the moment, one of my Arduino boards is generating the CTCSS, and is fed a transformer that is resonated at the tone freq. This is a transistor radio speaker transformer and the secondary is in series with the mic that is plugged into the headset connector of the "house" phone.
Eventually, the CTCSS generator and a PTT button will be installed inside the house phone so it can be used as a handset, headset or speaker phone.
When I get it working, I'll post full details.
Watch this space!