Digi XBee® Cellular LTE-M/NB-IoT module

Introduction

When operated in Digi's "bypass" mode, the u-blox SARA R410M based XBee3 can be implented as a DigiXBeeLTEBypass object - a subclass of DigiXBee and loggerModem. Bypass refers to the fact that XBee3's main processor is bypassed - acting only as a pass-through to the u-blox cellular component.

This LTE-M module can just about almost get by with only 500mA power supplied, but it definitely not ideal.

Manufacturer Documentation

The Digi product page for the LTE-M module is here: https://www.digi.com/products/embedded-systems/digi-xbee/cellular-modems/xbee3-cellular-lte-m-nb-iot

Modem Constructor

Example Code

// For the u-blox SARA R410M based Digi LTE-M XBee3
// NOTE:  According to the manual, this should be less stable than transparent
// mode, but my experience is the complete reverse.
#include <modems/DigiXBeeLTEBypass.h>

// NOTE: Extra hardware and software serial ports are created in the "Settings
// for Additional Serial Ports" section
const int32_t modemBaud = 9600;  // All XBee's use 9600 by default

// Modem Pins - Describe the physical pin connection of your modem to your board
// NOTE:  Use -1 for pins that do not apply
// The pin numbers here are for a Digi XBee with a Mayfly 0.x and LTE adapter
const int8_t modemVccPin    = A5;  // MCU pin controlling modem power
const int8_t modemStatusPin = 19;  // MCU pin used to read modem status
// NOTE:  If possible, use the `STATUS/SLEEP_not` (XBee pin 13) for status, but
// the CTS pin can also be used if necessary
const bool   useCTSforStatus = false;  // Flag to use the CTS pin for status
const int8_t modemResetPin   = 20;     // MCU pin connected to modem reset pin
const int8_t modemSleepRqPin = 23;     // MCU pin for modem sleep/wake request
const int8_t modemLEDPin = redLED;     // MCU pin connected an LED to show modem
                                       // status

// Network connection information
const char* apn = "xxxxx";  // APN for GPRS connection

// Create the modem object
DigiXBeeLTEBypass modemXBLTEB(&modemSerial, modemVccPin, modemStatusPin,
                              useCTSforStatus, modemResetPin, modemSleepRqPin,
                              apn);
// Create an extra reference to the modem by a generic name
DigiXBeeLTEBypass modem = modemXBLTEB;

LTE Network Selection

It is good practice to select which network you'll be connecting to based on your SIM card and signal availability. Example code for this can also be found in the menu a la carte example.

    // Extra modem set-up
    Serial.println(F("Waking modem and setting Cellular Carrier Options..."));
    modem.modemWake();  // NOTE:  This will also set up the modem
    // Turn off the cellular radio while making network changes
    modem.gsmModem.sendAT(GF("+CFUN=0"));
    modem.gsmModem.waitResponse();
    // Mobile Network Operator Profile - 0 = SW default
    //                                 - 1 = SIM ICCID selected
    //                                 - 2: ATT
    //                                 - 6: China Telecom
    //                                 - 100: Standard Europe
    //                                 - 4: Telstra
    //                                 - 5: T-Mobile US
    //                                 - 19: Vodafone
    //                                 - 3: Verizon
    //                                 - 31: Deutsche Telekom
    modem.gsmModem.sendAT(GF("+UMNOPROF="), 2);
    modem.gsmModem.waitResponse();
    // Selected network technology - 7: LTE Cat.M1
    //                             - 8: LTE Cat.NB1
    // Fallback network technology - 7: LTE Cat.M1
    //                              - 8: LTE Cat.NB1
    // NOTE:  As of 2020 in the USA, AT&T and Verizon only use LTE-M
    // T-Mobile uses NB-IOT
    modem.gsmModem.sendAT(GF("+URAT="), 7, ',', 8);
    modem.gsmModem.waitResponse();
    // Restart the module to apply changes
    modem.gsmModem.sendAT(GF("+CFUN=1,1"));
    modem.gsmModem.waitResponse(10000L);

Classes

class DigiXBeeLTEBypass

The class for any of Digi's cellular LTE-M XBee3 modules operating in Digi's "bypass" mode.

Defines

#define TINY_GSM_MODEM_SARAR4

The modem type for the underlying TinyGSM library.