Timz MESH Info Page
Inexpensive Audio Streaming
Method 1of 2 - Using a VoIP phone
for the MP3 method, click here
My goals were:
* No computer/server required to generate the stream; standalone self-contained encoder device
* under $100
* unattended operation
* no internet involved, mesh only
* the listener would not need any additional "decoder" hardware - or even a special driver to hear
the streamed audio at their end; simply call this modified phones IP address (or PBX number) and hear the streamed audio over your mesh phone.
I used a Grandstream 1630 telephone as the stand-alone encoding device by adding a 3.5mm audio input jack to it:
For a first test, I plugged a NWS weather radios audio into the Grandstream phones added jack... and configured the phone to "auto-answer". When anyone on our mesh grid dials this extension (either by PBX number or its IP address) it immediately answers and the caller hears the live NWS broadcast. It doesn't matter what audio source is used; but my initial testing was done with a weather radio.
This worked surprisingly well. Here is a diagram of the interface I put together:
Click Here to see LARGER version
The added 3.5mm stereo audio jack has a built-in switch; when you plug the external audio source into this jack, the switch disconnects the internal mic element used for spkr-phone operation, and the external audio is injected there. Not all switched jacks are the same; some switch the tip, others the ring. You want the switch function (regardless if it's on the tip ot ring) to be the positive side of the external audio & internal mic element (red wire).
I used pre-amp level audio from the weather radio; as speaker level audio would be waaaaay too high amplitude. I tapped into the weather radios volume control (high side of the control) which is line-level there, and it's amplitude stays the same on this high side - even if the radios volume control setting is changed.
Hints
* to take the phones case halves apart, remove many screws accessable from the bottom side of the phone. One screw is hidden underneath a small oval sticker.
* the mic element is on the front edge of the phone case, facing it's user. There are two wires going to the mic element from the phones main circuitboard. The red wire is the one that goes through the added jacks switched terminal.
* This circut of the Grandstreams mic element has high gain and mega AGC. When setting the input level amplitude via the interfaces potentiometer, it's easy to overdrive the phones circuit. It's a fooler because the AGC will try to compensate. My suggestion is to turn down the interface level pot until you can't hear any audio, then slowly turn it up. If you go too far, the audio will go from loud to somewhat weak as the AGC trys to compensate. It will work if overdriven, just that the sound is cleaner if you don't overdrive.
* Auto Answer is enabled by going into the phones PC setup, then Account 1, then Call Settings, then Auto Answer (change to Y). Click on SAVE at the bottom.
FAQ
* how much did all this cost?
I bought the GXV1630 used for $45. The stereo jack and plug were $10, I had the other components on hand... but it's probably another $10 worth there. So, about $65.* is the 1600 series phone -once modified - no longer operational as a regular mesh phone?
Unplug the external audio cable and everything returns to normal (just remember to turn off "auto-answer"). Even with the external audio cable plugged into the added jack, handset calls will still work fine.* why the audio coupling transformer?
The internal mic element in the Grandstream 1600 series phones is not grounded, is it a floating (balanced) design. Coupling transformers are an inexpensive way to convert a grounded source (in my case it was the line-level audio from my weather radio... which was conventional grounded type) over to a balanced source to properly feed the phones circuitry.* why not insert the external audio into the existing headset jack on the back of the phone ?
When auto-answering, the Grandstream 1600 series defaults to the speaker-phone mode, even though you might have a functional headset plugged in. There is no way to change this.* on the encoder phone - and during an auto-answered call... do you stil hear what's happening on the listener end?
yes. Just turn down the spkr-phone volume on the jack-added phone. When auto-answering, the phone emits a single soft beep letting you know it auto answered.* earlier you mentioned that this VoIp method "did not meet some of my original goals"
Yep. First off... I wanted this analog audio source to be played back via a computers browser and built-in audio/speakers. This VoIP method does require a VoIP telephone to access the audio stream.Secondly, I wanted this audio stream to be able to be heard by multiple devices simultaneously. This VoIP method is a one-at-a-time operation. Through a PBX though... you might be able to allow conference calling to this phones extension.
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