SparkFun LoRa Gateway 1-Channel Hookup Guide

Contributors: jimblom, Liquid Soulder

Turning a Gateway Into a Device

If you have a pair of ESP32 gateway's you can use one of them as a LoRaWAN device. This section will get you set up with our preferred LoRaWAN Arduino library and a simple example sketch to get started.

Get the Arduino-LMIC Library to Set Up a Device

If you have a pair of ESP32 Gateways and want to set one of them up as a LoRa device, we recommend using the Arduino-LMIC library. There seem to be many versions of the Arduino-LMIC library hanging around, we've had good success with the library forked by mcci-catena. If you don't want to use GitHub you can download an archived .zip file here. It will work for this guide but it may not be completely up-to-date.

To install the library, download the ZIP file and use the Arduino's "Add ZIP library" feature (Sketch > Include Library > Add .ZIP Library) to import the zip file into your Arduino sketchbook.

Configure LMIC

Before can use an example sketch in the LMIC library, you'll need to configure it. To configure the library, navigate to the "arduino-lmic" library in your ..{Arduino Sketchbook}/libraries folder. Then go to project_config and open lmic_project_config.h.

Here you'll define which frequency bands your LoRa device will use. You can also turn on debugging and enable/disable a host of features with definitions in this file.

Make sure you uncomment one (and only one!) of the "CFG..." declarations. If you're in the USA, uncomment #define CFG_us915. Ultimately, this frequency should match what you set in the gateway.

Below is my config file -- I've turned on debugging, because I'm a log junkie.

language:c
// project-specific definitions
//#define CFG_eu868 1
#define CFG_us915 1
//#define CFG_au921 1
//#define CFG_as923 1
// #define LMIC_COUNTRY_CODE LMIC_COUNTRY_CODE_JP   /* for as923-JP */
//#define CFG_in866 1
#define CFG_sx1276_radio 1

//#define LMIC_PRINTF_TO Serial
#define LMIC_DEBUG_LEVEL 2

//#define DISABLE_INVERT_IQ_ON_RX

If you try to use the "raw" example in this library, you'll need to uncomment DISABLE_INVERT_IQ_ON_RX, otherwise keep it commented-out.

Modify the "SPI.begin" call

Just to be sure your pin definitions are correct, I recommend modifying the SPI.begin line in arduino-lmic/src/hal/hal.cpp (line 136) to:

language:c
SPI.begin(14, 12, 13, 16);

This will ensure that your SPI pins are set correctly -- this may only be necessary if you're not using the custom "SparkFun LoRa gateway 1-Channel" Arduino board.

Load the Single-Channel Device Example

We've taken one of the examples in the Arduino-LMIC library and modified it to work more reliably with a single-channel gateway.

Click the button below to download the example. Then open up ESP-1CH-TTN-Device-ABP.ino:

Among the modifications in this example are the pin map between radio and ESP32 -- set with these lines:

language:c
const lmic_pinmap lmic_pins = {
  .nss = 16,
  .rxtx = LMIC_UNUSED_PIN,
  .rst = 5,
  .dio = {26, 33, 32},
};

We've also modified the enabled channels to only use a single channel with the lines below (note this modification hasn't yet been tested on non-US frequency bands).

language:c
// First disable all sub-bands
for (int b = 0; b < 8; ++b) {
  LMIC_disableSubBand(b);
}
// Then enable the channel(s) you want to use
LMIC_enableChannel(8); // 903.9 MHz

The spread factor is set near the end of setup() with the LMIC_setDrTxpow(DR_SF7, 14); line. This can be replaced with DR_SF8, DR_SF9, or DR_SF10 at the default 903.9MHz frequency.

You can't compile successfully until you fill in these lines:

// LoRaWAN NwkSKey, network session key
// This is the default Semtech key, which is used by the early prototype TTN
// network.
static const PROGMEM u1_t NWKSKEY[16] = { PASTE_NWKSKEY_KEY_HERE };

// LoRaWAN AppSKey, application session key
// This is the default Semtech key, which is used by the early prototype TTN
// network.
static const u1_t PROGMEM APPSKEY[16] = { PASTE_APPSKEY_KEY_HERE };

// LoRaWAN end-device address (DevAddr)
static const u4_t DEVADDR = 0xPASTE_DEV_ADDR_HERE;

with something. If you want to test the gateway right now go ahead and fill the two arrays with 16 bytes each and the DEVADDR with a 4-byte wide number. If you do this and upload the code then you should see the gateway receiving messages. (If you're having trouble make sure that the device and the gateway are configured to use the same channel and spreading factor).

If you are OK waiting then leave these blank until you get your actual keys and device address from The Things Network in the next section.