Asterisk Siemens M20

Siemens M20 asterisk howto

These are my experiments with the Siemens M20 GSM terminal and Asterisk

From Siemens M20 product page
The Siemens M20 Terminal is the ideal solution for mobile and stationary industrial applications in telemetry, telematics and telephony. Its functions are fully compatible with those of all cellular engines.

"Alfred R. Nurnberger" (alfred AT flosys DOT com) wrote:
You have 2 issues here to deal with:

  1. the hardware to connect the M-20 to Asterisk
  2. a channel driver controling the M-20

This is a update on how to do connect the M20 to your PC soundcard

a) Connect the M20 to the PC and log in to the GSM net
Connect the M20 to the COM1 port, set 19200bps � you should be able to do type AT and hit CR. The modem should then display OK

Logging in to the GSM net is done by the at commend
1234 is your pin code. The light on the M20 should then stop blinking to signal that you are logged in to the GSM net.

Dialing a number

b) Connecting the PC soundcard to the M20

M20 audio interface
(info from the Siemens M20 technical manual)
The M20 has a 4pin phone connector (I believe it is called RJ9) Make sure the plug is 4pin. A 6pin plug will not fit.

PC audio interface
(info from
Audio output
Most soundcards have mini jack stereo output. But this is not needed when connecting to the M20. I use a mono jack.
Polarity on the audio output is:
The tip of the jack is left/right channel plus. And the inner is left/right channel minus.
See web reference above for detailed information.

Audio input
Has the same polarity as the audio input.

How to connect:

Pin and colorsSignalFunctionCommentsJack
Pin 4=yellowMICPMicrophone plusDifferential input must be AC-coupled input resistance: 11�22 MohmThis will go to the PC speaker jack (green)Tip of the jack
Pin 1= blackMICNMicrophone minusDifferential Input, internally, must be AC-coupled, input resistance: 11�22 MohmThis will go to the PC speaker jack (green)
Pin 3=greenSPPSpeaker plusmin. load resistance: 32,max. load capacitance: 100 pF,should be AC-coupledThis will go to the PC Mic jack (pink)Tip of the jack
Pin 2= redSPNSpeaker minusmin. load resistance: 32,max. load capacitance: 100 pF,should be AC-coupled,This will go to the PC Mic jack (pink):

If possible use one pink and one green jack. This is the standard colors for Mic input and speaker output. And you avoid mixing them.

Q: I do not know how to write a channel driver. I hope somebody can point me in the right direction.
A: Maybe the modified chan_oss of the hardware-phone-to-sound-card project (see below) can help? Still the signalling question will remain unsolved, though...

See also

Go back to Asterisk

Created by: JustRumours, Last modification: Wed 16 of Nov, 2005 (23:29 UTC)
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