STM32 LoRa message communication

Introduction

This tutorial introduces message communication using LoRa Mary.

Before you start

This example requires two devices, each combining AP03 STM32 MCU and AC07 LoRa Mary: a transmitter and a receiver. They use different source programs. Choose Arduino IDE or PlatformIO and prepare the upload environment first.

Use Leafony’s arduino-LoRa and arduino-tca9536 libraries. Match the dependencies of the chosen source instead of substituting other implementations with similar names. See How to run an example for the basics of obtaining and uploading the source.

Required items

Transmitter configuration

• AC07 LoRa Mary
• AP03 STM32 MCU
• AV04 2V–4.5V
• AZ67 AAA battery holder
• AZ63 Nut Plate
• Two M2 × 12 mm screws
• Three AAA batteries

Receiver configuration

Use Back to back to keep the USB cable from covering the LoRa Mary antenna area.

• AC07 LoRa Mary
• AP03 STM32
• AZ01 USB
• AX07 Back to back
• AZ63 Nut Plate 2P
• Two M2 × 8 mm screws
• Two M2 × 10 mm screws
• USB cable
• Computer

Source code

Obtain the transmitter and receiver sources for the same development tool. For Arduino IDE, open the complete sketch folder. For PlatformIO, open the complete project including platformio.ini and src. The distribution links point to master or main, so their contents may change between downloads.

Transmitter

• Arduino source
• PlatformIO source

Receiver

• Arduino source
• PlatformIO source

Run the example

1. Check the transmitter and receiver sources and match communication settings such as frequency, spreading factor, and signal bandwidth. Refer to the downloaded source for setting names and values.
2. Upload the transmitter and receiver programs to their respective AP03 leaves. If PlatformIO’s upload_port or upload_command still contains settings for an older computer environment, follow the current upload configuration instructions.
3. After uploading, switch each AP03 to Run and reset it. Open the receiver’s serial monitor at 115200 bps.
4. Check that the receiver repeatedly displays hello, the transmission count, and received signal strength (RSSI, in dBm). The -37 below is an example; it varies with distance and installation conditions.

Received: hello 0, RSSI: -37

The transmitter log alone does not confirm reception. Check that the count displayed by the receiver updates.

Troubleshooting

Symptom	What to check
LoRa.h or TCA9536.h is not found	Check that the required libraries are installed for the selected development tool
Build succeeds but upload fails	Check AP03 upload mode, the USB port, and PlatformIO’s upload command
Execution stops while initializing LoRa or the IO expander	Turn off the power, check the AC07 and AP03 connections, and compare the assembly with the source’s target configuration
Transmission starts but nothing is received	Check that both devices start in Run mode, communication settings match, and the receiver’s serial port and 115200 bps setting are correct

Keep USB cables and metal from covering the antenna area. For connection basics, see the AC07 reference and FAQ.