More playing with Asterisk

I have been playing some more with Asterisk and I’ve got 2 useful bits to share.

MP3 Voicemail

The simple one first, a recent update to Android (not sure what exactly) means it won’t playback wav files attached to emails. This is a problem as when Asterisk records a voicemail it can be configured to email the recording in wav to mailbox owner. A little bit of googling turned this up http://bernaerts.dyndns.org/linux/179-asterisk-voicemail-mp3. It needed updating a little to get it to work on my Raspberry Pi.

First I needed to change one of the sed line to match WAV not wav to fix the file name from this:

...| sed 's/.wav/.mp3/g' > stream.part3.mp3.head

to this:

...| sed 's/.WAV/.mp3/g' > stream.part3.mp3.head

Secondly lame doesn’t like the encoding for the wav file (I think it’s because the stored values are unsigned) so we need to run it through sox to fix it first.

sox stream.part3.wav -e signed stream.part3a.wav
lame -m m -b 24 stream.part3a.wav stream.part3.mp3

This not only makes it so I can listen to the messages on my phone and tablet it also makes the mails smaller so they take up less bandwidth.

Using a 3G Stick to make calls

Having used OBi110 to hook my Asterisk VoIP rig up to a standard phone line I was looking for a way to hook a mobile phone to the system. There are 2 options with Asterisk, chan_bluetooth and chan_dongle.

Chan_bluetooth uses a bluetooth connection to a mobile phone to make and receive calls. I had a look at this but it meant keeping phone plugged into a charger and having another bluetooth adapter plugged in.

Chan_dongle work with certain Huawei 3G USB modems. These 3G sticks are basically full phones with a USB interface. I’ve already been using one of listed modems for my SMS/MMS project and I had a spare one kicking around. It needed the firmware updating to make it work, which was a bit of a challenge as it required setting up a real Windows machine as I couldn’t get it to work in a VM.

Setting up the dongle was a little tricky at first as I couldn’t get a set of udev rules to match the stick properly to ensure it always ends up with the same device names. The code does let you specify the stick using it’s IMEI which helps if you have multiple sticks plugged into the same computer.

Once configured it was easy to set up the extensions.conf to allow making and receiving calls. The main reason for setting this up was to have a portable VoIP rig that I can take to different places and not have to worry about a fixed phone line. There is a upcoming hackday that I have a plan for.

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