Well it was easier than expected. I had this Adafruit FONA 808 board sitting around from an older projected and figured hey why not try to hook it up to the Pchip. I was able to connect it up, make a call, and send an SMS from the terminal console using the "screen" program. Of course, you must have a SIM card to place in the FONA. Here is a gist of what to do if anyone was curious:
NOTE: I TAKE NO RESPONSIBILITY IF YOU DAMAGE YOUR POCKET CHIP. THIS WORKED FOR ME, THATS ALL I KNOW
1.Wire the FONA to the Pchip.
Note: the FONA must have its own LIPO/LIion battery hooked into the JST connector in order to work. I supposed you could wire it to the pchip 3v but I DID NOT try that. Also required is the GSM antenna.
I used the break out solder points at the top of the pocket chip
FONA TX -> Pocket CHip UART RX
FONA RX -> Pocket Chip UART TX
FONA GND -> Pocket Chip GND
FONA KEY -> Pocket Chip GND
FONA VIO -> Pocket Chip +3v
2.Power up Pocket Chip:
-you should notice the blue PWR LED of the FONA lit solid and the red NET LED starting to blink
3.Install screen (I ssh'd into my Pocket Chip):
sudo apt-get install screen
4.Disable getty on TTYS0 (this may not be necessary but I did it and it worked fine):
systemctl stop serial-getty@ttyS0.service
screen /dev/ttyS0 115200
6.You should now see a blank screen where you can type in AT commands:
type: "AT" (without quotes) and you should receive "OK" as a response. this verifies the FONA and Pocket CHIP are talking to one another!
Here are some AT commands to try:
ATI - Get the module name and revision
AT+CMEE=2 - Turn on verbose errors (handy for when you are trying out commands!)
AT+CCID - get the SIM card number - this tests that the SIM card is found OK and you can verify the number is written on the card
AT+COPS? Check that you're connected to the network
AT+CSQ - Check the 'signal strength' - the first # is dB strength, it should be higher than around 5. Higher is better. Of course it depends on your antenna and location!
AT+CBC - will return the lipo battery state. The second number is the % full (in this case its 92%) and the third number is the actual voltage in mV (in this case, 3.877 V)AT+CMGF=1 - this will set it to TEXT mode not PDU (data) mode. You must do this because otherwise you cannot just type out the message.
To Send a text msg:
You will get a '>' prompt for typing. Type out your message and when you are done send a [Control-Z] on an empty line to send
ATDnnnnn; (Don't forget the ; at the end!)
If they pick up you'll hear it in the headset, if no pickup, you'll get a NO CARRIER return
Once you are done chatting, you can hang up by sending ATH
Of course you need a hands-free headphone/mic device to plug into the FONA in order to hear the your caller and to talk!
7.To exit from screen: Ctrl+a and then Ctrl+z
Next up: create a PPP connection to use the data connection of the FONA with the Pocket CHIP!