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04-GSM-modem.md

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GSM Modem

raspberry-pi-4-labelled

We will need the SIM card in its standard card size (25 mm by 15 mm).

  • Please take note of the phone number, PIN and PUK number of the SIM card (you might need them in Calvi)
  • Place the SIM card in the WaveShare HAT (gently, very gently). All SIM cards need to be activated (see below)
  • Connect the GNSS (GPS) and GSM atennas to the Modem
  • Connect the WaveShare HAT with the Rasbperry Pi and fix with screws
  • Power on the Rasbperry Pi
  • Power on the WaveShare HAT

SIM card activation: by using the procedure "SMS" below, send an SMS to 8804 with:

  1. The word IDENT
  2. Twice the phone number of the SIM card, separated by space. For example IDENT 0470123456 0470123456.

The Modem uses a series of so-called AT commands. All commands start with AT (meaning 'attention'). All commands end with the characters \r\n (carriage return, line feed). The basic commands used here are the following:

Command Description Return value
AT Test Modem OK
AT+CPIN? Check if the SIM card is unlocked
AT+CPIN="1234" Unlook SIM using pin 1234
AT+CREG? Network registration status
ATD0032XXXXXXXXX; Call a phone number 0032XXXXXXXXX (replacing all X by numbers)

Minicom first tests

First, start the Waveshare HAT (long push on power button PWRKEY)

sudo minicom -D /dev/ttyS0
  • Try these commands, they should not return ERROR (where 1234 is your pin):
AT
# output OK
AT+CPIN="1234"

AT+CREG?

Some CREG info: https://web.archive.org/web/20230121160033/https://docs.eseye.com/Content/ELS61/ATCommands/ELS61CREG.htm

  • Command to call a phone number (do not forget the final semicolon and the telephone prefix)
ATD0032XXXXXXXXX;

SMS

Command Description Return value
AT+CMGF=1 Set the format of messages to Text mode
AT+CSCA="some number" set the SMS Service Center Address
AT+CMGS="phone_number" send an SMS message to a GSM phone (wait for the > prompt and terminate the message with CTRL+Z

In Julia, SMS messages should be terminated by "\x1a\r\n" (CTRL+Z, carriage return, line feed).

Optional, test to send a SMS via minicom:

AT
# output OK
AT+CPIN?
+CPIN: READY

# output OK
AT+CMGF=1
# output OK
AT+CSCA="0032475161616"
# output OK
AT+CMGS="0032111111111"
> your message without special characters
>
+CMGS: 9

# output OK

where 0032475161616 is the local SMS Service Center number and 0032111111111 its the recipient GSM phone number.

cell phone operator local SMS service center
Proximus, Belgium 0032475161616
Orange, Belgium 0032495002530

To exit minicom, type Ctrl+A x.

Global Navigation Satellite System (GNSS)

Examples of GNSS include Europe’s Galileo, the USA’s NAVSTAR Global Positioning System (GPS), Russia’s Global'naya Navigatsionnaya Sputnikovaya Sistema (GLONASS) and China’s BeiDou Navigation Satellite System.

Command Description Return value
AT+CGNSPWR? query if GNSS is powerd on
AT+CGNSIPR? query the GNSS baud rate
AT+CGNSPWR=1 power GNSS on
AT+CGNSINF get time and coordinates (if available)

More information about NMEA is available at http://aprs.gids.nl/nmea/.

Tests in Julia

Open the serial port:

using LibSerialPort
sp = LibSerialPort.open("/dev/ttyS0", 115200)

Execute a command:

write(sp, "AT\r\n")

Read its output

if bytesavailable(sp) > 0; println(String(read(sp))); end
# output
# OK