wayne roberts / Mbed OS chat_sx127x

UART console application for testing SX1272/SX1276

Dependencies:   SX127x

This is a UART console test application for using SX127x library driver for SX1272/SX1276 radio transceivers. Serial console is provided at 57600bps. Refer to Serial Communication with a PC for information about using the serial port with your PC.

Using this command interface, you can exercise the functionality of radio chip without needing specialized software application for your PC.

Commands which can be used include ? to list available commands, or . to query status from radio chip, for example. The serial console allows you to configure the radio chip, such as setting spreading factor, bandwidth, operating frequency, etc.

A simple chat application is provided to try communications between two boards. The SX127x library object is instantiated with pin assignments generic arduino headers, but can be easily reassigned for any mbed board.

The same driver library can operate for both SX1272 and SX1276. Upon starting, the driver auto-detects whether SX1272 or SX1276 transceiver chip is connected by attempting to change the LowFrequencyModeOn bit in RegOpMode register. If this bit can be changed, then the radio device is SX1276. This bit is not implemented in SX1272. A few of the radio driver functions select behavior based on this detection. The differences between these two devices is small, from a software perspective.

Using with SX1276MB1xAS Shield

This component plugs into any board with arduino uno headers.

There are two different version of this shield. European version (MAS), and North American (LAS). The LAS shield uses PA_BOOST transmit pin to permit +20dBm power. The MAS version uses RFO transmit pin in Europe. This software reads RF switch pin (A4 pin) pulling resistor to determine which type of shield is installed.

Using with your own production board

This software is useful for validating RF performance your own LoRa board design, because only two external pins needs to be provided to PC (UART TX/RX). You can select an mbed platform which matches the CPU on your own board. If the memory size doesnt match exactly, you can export the program to an offline toolchain and edit the target type or linker file there.

Transmitter Test Guidelines

FSK mode is used for transmitter testing, because an unmodulated carrier can be sent, permitting easy measurement of TX power and frequency error.

commands used for transmitter testing:

• frf915.0 change to your desired RF center frequency (in this case 915MHz)
• L to toggle the radio chip into FSK mode.
• fdev0 to configure TX frequency deviation to zero, to put the transmitted carrier on the center frequency.
• pas to select which TX pin is connected to antenna matching (RFO vs PA_BOOST).
• op<dBm> to configure TX power.
• If you desire to test higher power PA_BOOST, use ocp<mA>
• w 01 03 put radio chip into transmit mode (skips writing to FIFO). This will cause radio to transmit preamble, because the FIFO is empty in TX mode. Since Fdev is zero, an unmodulated carrier is sent.
• Spectrum analyzer can now be used to to observe TX power, harmonics, power consumption, or frequency error.
• stby to end transmission, or use h to reset radio chip to default condition.
• Use period . command at any time to review current radio configuration.

LoRa transmitter testing

• use L command to toggle radio into LoRa, if necessary.
• Normally the tx command is used to manually send single packets.
• txc will toggle TxContinuousMode in LoRa modem to send continuous modulated transmission.
• Useful for checking adjacent channel power.
• enter txc again to end transmission.

Receiver Test Guidelines

FSK mode is used for receiver sensitivity testing, allowing the use of a BERT signal generator (such as R/S SMIQ03B). Using this method provides real-time indication of receiver sensitivity, useful for tuning and impedance matching. The radio chip outputs DCLK and DATA digital signals which are connected back to BERT signal generator.

commands used for receiver testing:

• L to toggle the radio chip into FSK mode.
• datam to toggle FSK modem into continuous mode. This disables packet engine and gives direct access to demodulator.
• configure DIO1 pin to DCLK function, and DIO2 pin to DATA function:
  • dio command to list current DIO pin asignments
  • d1 to cycle DIO1 function until Dclk is selected
  • d2 for DIO2, only Data function is available in FSK continuous mode
• frf915.0 change to your desired RF center frequency (in this case 915MHz)
• rx to start receiver
• stby to disable receiver

Full command list

Arguments shown in square brackets [] indicate required. <> are optional, where leaving off the argument usually causes a read of the item, and providing the value causes a write operation. You should always have the radio chip datasheet on-hand when using these commands.

Hitting <enter> key by itself will repeat last command.
<Ctrl-C> will cancel an operation in progress.

command list: common commands (both LoRa and FSK)

command list: LoRa modem commands

command list: FSK modem commands

added fsk back-to-back packet demonstration