sx127x_demo SX127X Radio

This example demonstrates the use of the SX127X radio.

Overview

The sx127x_demo application exercises the SX127X low-power wide-area network (LPWAN) radio driver in both transmit and receive modes. It is typically enabled via a board defconfig together with CONFIG_LPWAN_SX127X and the appropriate SPI and GPIO wiring for the target module.

Default configuration

Unless explicitly overridden in the board or application configuration, the SX127X driver uses the following relevant defaults:

  • RF frequency: CONFIG_LPWAN_SX127X_RFFREQ_DEFAULT (board-specific, for example 433 MHz, 868 MHz or 915 MHz).

  • TX power: CONFIG_LPWAN_SX127X_TXPOWER_DEFAULT. The global default is 17 dBm, which provides a stronger and more reliable link than the previous 14 dBm default.

  • CRC: CONFIG_LPWAN_SX127X_CRCON. The global default is 1 (CRC enabled), so payloads are protected by a checksum and corrupted frames are rejected.

Individual boards may override these values in their defconfig files. For example, some boards tested with integrated SX1276 modules may set CONFIG_LPWAN_SX127X_TXPOWER_DEFAULT=20 and adjust CONFIG_LPWAN_SX127X_RFFREQ_DEFAULT to match the module’s band.

Short-range FSK testing

When running short-range FSK tests (for example, two modules placed around one meter apart on a lab bench), the following settings are recommended:

  • Keep CONFIG_LPWAN_SX127X_TXPOWER_DEFAULT at 17 dBm or higher (some modules work well at 20 dBm) to avoid marginal RSSI values that can lead to intermittent reception.

  • Ensure CONFIG_LPWAN_SX127X_CRCON=1 on both transmitter and receiver so corrupted frames are discarded instead of being printed with incorrect data.

These defaults are based on empirical testing reported by users and are intended to provide robust communication without requiring additional per-board tuning.

Troubleshooting

If the receiver occasionally shows no data, truncated data, or payloads that do not match what was transmitted, check the following:

  • Verify that the RF frequency and modulation settings are identical on both sides.

  • Inspect the reported RSSI and SNR values; very low RSSI at short distance can indicate insufficient TX power or antenna issues.

  • Confirm that CRC is enabled and that both peers are configured consistently (either both with CRC enabled or both with it disabled, though enabling CRC is recommended).

Adjusting TX power or antenna placement and ensuring consistent CRC settings on the link typically resolves data integrity problems seen in simple FSK tests.