In order to make the most of the fact that I have had to test out the PCM interface from Cinterion modules and from Bluegiga Bluetooth modules, I will post about it as it will be of great help to those who want to develop a hands-free GSM device (via Bluetooth). In order to not complicate matters, I will post the information in a simplified, practical way. Well, here we go…

1.- Let’s take a DSB75 evaluation board where we insert the Cinterion GSM module that we want to use (a TC63i, a TC65i, a PH8 etc.) In my case I have a TC65i.

2.- Locate the pins on the DSB75 evaluation board that correspond to the PCM audio pins. They specifically correspond to the board’s x703 connector. In this connector we will see 7 pins: TXDAI, RXDAI, FS, BITClk, FSIN, BCLKIN and GND.

pcm-dsb75

3.- Out of these 7 pins, we only need 5 that are using PCM. The choice you make will depend on whether you use the Cinterion module in PCM MASTER mode or PCM SLAVE mode.  If you use the Cinterion module in PCM MASTER mode, use the TXDAI, RXDAI, FS, BITCLK and GND pins. If we use the Cinterion module in PCM SLAVE mode, use TXDAI, RXDAI, FSIN, BCLKIN and GND pins. The following photo shows how I used it in SLAVE mode with the cables connected to these 5 pins.

dsb75-conexiones

4.- We took a Bluegiga development kit (the simplest to use is the WT32 Bluetooth module). The reason for choosing this kit is because it has the PCM pins available in the development kit’s PCB. In Bluegiga’s PCB you can easily see where the PCM pins are due to the good screen.

wt32-conexiones

5.- Connect the GSM Cinterion’s PCM pins with the Bluegiga WT32 Bluetooth module’s PCM pins. Basically you have to connect the pins as follows:

TC65i  (Slave)    WT32 (Master)

RXDAI             OUT
TXDAI             IN
FSIN                SYNC
BCLK               CLK
GND                GND

What if you want the opposite? If we wanted to use the GSM module in MASTER mode it would be like this:

TC65i  (Master)   WT32  (Slave)

RXDAI              OUT
TXDAI              IN
FS                       SYNC
BITCLK            CLK
GND                  GND

So once you have done this, all of the hardware is connected. Now you need a Bluetooth hands-free earpiece. I have one from Plantronics with MAC Bluetooth: 00:03:89:a5:a6:72 (I mentioned it because I will use it later).

6.-The next step is to configure the WT32 Bluetooth module to route audio to/from the PCM interface. We do this by sending the following command to the WT32 module via a HyperTerminal at 115200,8,N,1:

SET CONTROL AUDIO PCM PCM

7.- We’ve set up the PCM configuration to the Bluetooth module. Due to the complexity of the different PCM configurations, we use an Excel provided by Bluegiga. With this excel we can indicate the configuration that we want and this way we easily obtain the PSKEY_PCM_CONFIG32 value that we need to configure the PCM. In this case PSKEY_PCM_CONFIG32 has a value of 0×08400000.

config-audio-pcm

As in the previous point we can configure the PSKEY by a command from the HyperTermainal:

SET CONTROL PCM 08400000 006C

8.- Now we are going to configure the Cinterion GSM module to use the audio’s digital interface. These commands can have different functions depending on the model used. I am going to do it with a TC65i. Therefore, from a HyperTerminal we send:

AT^SAIC=1,1,1,1,1,1

So let’s configure the module to use the PCM digital audio in SLAVE mode at 512MHz and Long Frame.

At this point we have already configured both the Bluetooth module and the GSM module.

So now let’s try the audio!!!!

9.- From the Bluetooth hands-free earpiece (that I imagine is already paired with the Bluegiga Bluetooth module), we can connect to the Bluegiga Bluetooth module (by pressing the only button that it has).

10.- Next we physically connect the TC65i module’s ASC0 RS232 serial port to the WT32 Bluetooth module’s serial port with a serial cable crossover.

11.- We make a GSM audio call from a mobile telephone to the TC65 GSM module. On receiving the call, the module lets out a “RING” from the serial port that will be received by the Bluetooth module in order to inform the Bluetooth earpiece that there is an incoming call (we hear the typical beep beep of an incoming call). We answer the call by pressing the button on the Bluetooth earpiece.

12.- Once you have done this, we answer the voice call in the GSM module with the typical ATA command. If everything has gone well up to now, we will be talking with our hands-free Bluetooth earpiece, connected via Bluetooth to the Bluegiga WT32 module and this in turn is connected to the Cinterion GSM module through the PCM interface.

Well, that’s all for today. This post is perhaps a bit complicated to understand if you don’t have the devices in front of you. But you’ll see that if you ever need to do something similar, this post will be a gem and it will save you lots of working hours. I’ll be fine if I ever need to do it again because I have had to assemble this 3 times over the years. I always think that I won’t forget how to do it but something always slips my mind. From now on this won’t happen ;)

 

 


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