Prerequisites

You will need the following to follow this lab:

1. LoPy module

2. LoPy expansion board (optional, but advised - alternatively a USB-uart module)

3. A piece of wire.

4. Arduino IDE on your computer.

5. Install the ESP32 board support libraries for Arduino, following the steps on their github repo.

6. Install the LMIC library from my github repository.

7. On the TTN Console, create an application and a device. In settings change the device to ABP and disable Frame Counter Checks. We will later come back here for the NWKSKEY, APPSKEY and DEVADDR.

Compile the example

Open the Arduino IDE and go to File->Examples->IBM LMIC framework->ttn abp.

Around line 64, change the pin-mapping block of code. Replace the original with the following:

const lmic_pinmap lmic_pins = {
    .mosi = 27,
    .miso = 19,
    .sck = 5,
    .nss = 17,
    .rxtx = LMIC_UNUSED_PIN,
    .rst = 18,
    .dio = {23, 23, 23}, //workaround to use 1 pin for all 3 radio dio pins
};

At the top of the sketch, change NWKSKEY, APPSKEY and DEVADDR to your keys, as from the TTN console.

// LoRaWAN NwkSKey, network session key
static const PROGMEM u1_t NWKSKEY[16] = { 0x2B, 0x7E, 0x15, 0x16, 0x28, 0xAE, 0xD2, 0xA6, 0xAB, 0xF7, 0x15, 0x88, 0x09, 0xCF, 0x4F, 0x3C };
// LoRaWAN AppSKey, application session key
static const u1_t PROGMEM APPSKEY[16] = { 0x2B, 0x7E, 0x15, 0x16, 0x28, 0xAE, 0xD2, 0xA6, 0xAB, 0xF7, 0x15, 0x88, 0x09, 0xCF, 0x4F, 0x3C };
// LoRaWAN end-device address (DevAddr)
static const u4_t DEVADDR = 0x03FF0001;

In the Arduino IDE go to Tools->Board->ESP32 Dev Module.

Click on Verify. If you installed and change everything correctly, this should succeed.

If you get the following error, it means you forgot to change the pin-mapping block:

sorry, unimplemented: non-trivial designated initializers not supported
exit status 1
Error compiling for board ESP32 Dev Module.

If you get the following error, you need to change the radio type LMIC is expecting:

Starting
FAILURE
…/Documents/Arduino/libraries/<wbr>arduino-lmic-master/src/lmic/<wbr>radio.c:689

To change the setting go to …/Documents/Arduino/libraries/arduino-lmic-master/src/lmic/config.h  and change the lines about the radio to:

// This is the SX1272/SX1273 radio, which is also used on the HopeRF
// RFM92 boards.
#define CFG_sx1272_radio 1
// This is the SX1276/SX1277/SX1278/SX1279 radio, which is also used on
// the HopeRF RFM95 boards.
//#define CFG_sx1276_radio 1

Program the LoPy

Plug your LoPy into the expansion board, and plug a micro USB cable from the expansion board into your computer.
Alternatively if you do not have an expansion board, you should connect a USB to serial converter to the correct pins on the LoPy.

Connect a piece of wire from pin G23 on the expansion board to GND.
Alternatively you can short pin 2 on the LoPy to GND.

Press and release the reset button.

The LoPy is now in bootloader mode and ready to accept new code. In the Arduino IDE, got to Tools->Port and choose the port the LoPy is connected to.

Click on Upload.

After you see "Done uploading" you can remove the piece of wire between G23 and GND, and then reset the LoPy again.

Open the Serial Monitor, change it to 115200 baud, and you should see the following:

Starting
Packet queued
376953: EV_TXCOMPLETE (includes waiting for RX windows)

Conclusion

You have now successfully uploaded Arduino code to your LoPy, and you successfully sent a packet via the LoRa radio.

Now you can change the example code to create a nice use case around the LoPy!

All you need to do to put your code on the LoPy is to repeat these simple steps:

1. While pins G23 and GND are shorted, reset the LoPy.

2. Upload the code from the Arduino IDE.

3. Remove the connection between G23 and GND and reset the LoPy again.

To go back to the original micro python environment on the LoPy, just follow the procedure to do a "firmware update over USB".