What is AT LoRa Dongle?

Ropixon AT-USB LoRa Dongle enables sending and receiving all LoRa packets! Just configure it properly using intuitive AT commands via serial line.

• No programming required.
• It's suitable for rapid development, testing, or creating your own wireless LoRa link.

What is it for?

AT LoRa Dongle is suitable for:

• Testing and development of LoRa applications
• Point-to-Point communication over long distances
• Range tests - measuring capable of LoRa connection distance
• Sensor networks - collecting data from remote sensors
• RF testing - testing RF parameters, CW transmission
• Scanning - capturing random packets transmitted over the air

Overview

When sending packets, no additional "wrapping" or encryption of data is used - you always send RAW (hex or ASCII) data. The same applies to reception.

Additional functions: AT LoRa dongle has 8 aux pins - you can set its logical level or activate PWM on it - just through the AT commands.

For quick start:

1) Install driver for serial interface CP2102 according to your system: Download drivers

2) Connect AT dongle to USB and set desired LoRa parameter configuration (or leave defaults)

3) Send your first LoRa packet via AT commands:

• Send data in ASCII: AT+RF_TX_TXT=Hello, this is AT LoRa dongle Ropixon!
• Send data in HEX: AT+RF_TX_HEX=48656C6C6F2C2074686973206973204154204C6F526120646F6E676C6520526F7069786F6E21

4) Reception is activated automatically - output format HEX/ASCII can be selected using AT+RF_RX_FORMAT=HEX|ASCII, ?

Status LEDs

The dongle has 3 LEDs serving these functions:

• RED => Reception of new AT commands
• GREEN => System LED - indicates proper operation of the entire device
• BLUE => Reception or transmission of LoRa data

*Note: RF path is optimized for 868 MHz band (EU: 863-870 MHz, USA: 915 MHz). The further from the operating band, the less power can be transmitted/received. *

Aux pins

The AT dongle has 8 aux pins that can be "manually" controlled or run PWM modulation (maximum frequency 1 kHz): AT+AUX_PULSE=<pin:1-8>,<period_ms>,<duty%:0-100>

Main Features:

• RF LoRa Chip: SX1262 LoRa transceiver from Semtech - Datasheet here: SX1262
• Interface: USB (Virtual COM port) - Drivers can be found here: Download drivers
• Control: AT commands via serial line
• Supported baud rates: 9600, 19200, 38400, 57600, 115200, 230400 (default/recommended)
• Frequency: 150 MHz - 960 MHz (typically 863-870 MHz for EU, 915 MHz for USA), RF path is optimized for 868 MHz band, but 915 MHz operation is also fine. The further from the operating band, the less power can be transmitted/received from the dongle.
• TX power: up to 22 dBm
• Spreading Factor: SF5 to SF12
• Bandwidths: 7.81 kHz to 500 kHz

Serial terminal connection configuration:

• Baud rate: 230400 (default)
• Data bits: 8
• Parity: None
• Stop bits: 1
• Flow control: None
• Line ending: CR+LF (\r\n)

Communication test

Send command: AT (or AT+HELP) Dongle will respond with a list of all available commands. AT+IDENTIFY Dongle will respond "Ropixon AT-USB LoRa_Dongle v1.0.0 UID:xxxxxxx......."

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AT Commands - Complete Overview

Basic System Commands

Command	Description	Example
AT	Print help	AT
AT+HELP	Display all available commands	AT+HELP
AT+IDENTIFY	Return unique device ID	AT+IDENTIFY
AT+FACTORY_RST	Reset all settings to factory defaults and restart	AT+FACTORY_RST
AT+SYS_RESTART	System restart	AT+SYS_RESTART
AT+UART_BAUD	Set/query baud rate, restart on change	AT+UART_BAUD=230400

LoRa TX Parameters (transmission)

Command	Description	Value Range	Example
AT+LR_TX_FREQ	TX frequency in Hz	-	AT+LR_TX_FREQ=869525000
AT+LR_TX_POWER	TX power	-17 to 22 dBm	AT+LR_TX_POWER=14
AT+LR_TX_SF	Spreading Factor	5 to 12	AT+LR_TX_SF=7
AT+LR_TX_BW	Bandwidth	0-9 (see table)	AT+LR_TX_BW=7
AT+LR_TX_CR	Coding Rate	45, 46, 47, 48	AT+LR_TX_CR=45
AT+LR_TX_PREAMBLE	Preamble length	symbols	AT+LR_TX_PREAMBLE=8
AT+LR_TX_SYNCWORD	Sync word	0x0000-0xFFFF	AT+LR_TX_SYNCWORD=0x3444
AT+LR_TX_CRC	CRC enable/disable	0, 1	AT+LR_TX_CRC=1
AT+LR_TX_IQ	IQ inversion	0, 1	AT+LR_TX_IQ=0
AT+LR_TX_HEADERMODE	Header mode	0=explicit, 1=implicit	AT+LR_TX_HEADERMODE=0
AT+LR_TX_LDRO	Low Data Rate Optimization	0=off, 1=on, 2=auto	AT+LR_TX_LDRO=2

LoRa RX Parameters (reception)

Same parameters as TX, just replace TX with RX:

• AT+LR_RX_FREQ, AT+LR_RX_SF, AT+LR_RX_BW, etc.

Important: AT+LR_RX_PLDLEN - Payload length (required for implicit header mode)

Bandwidth Values

Value	Bandwidth
0	7.81 kHz
1	10.42 kHz
2	15.63 kHz
3	20.83 kHz
4	31.25 kHz
5	41.67 kHz
6	62.5 kHz
7	125 kHz
8	250 kHz
9	500 kHz

Quick Setup (all RF parameters at once)

TX configuration: AT+LR_TX_SET=SF:7,BW:7,CR:45,Freq:869525000,IQInv:0,HeaderMode:0,CRC:1,Preamble:8,LDRO:2,Power:22

RX configuration: AT+LR_RX_SET=SF:7,BW:7,CR:45,Freq:869525000,IQInv:0,HeaderMode:0,CRC:1,Preamble:8,LDRO:2

How to navigate all parameter configurations? Here is calculator showing what happens to data/packet with different modulation settings (select SX1262 as device):

• Online calculator: Semtech LoRa Calculator
• Offline calculator (PDF): Semtech SX1262 Calculator

A simple rule applies: For high data rates, choose high BW and low SF - however, this reduces the receiver's ability to obtain data at greater distances. On the other side, if signal is weak (poor transmission conditions) SF needs to be increased and BW decreased. All this affects packet Time on Air (TOA). TOA can also be easily verified using the command: AT+RF_GET_TOA=<packet_size_bytes>, the result is calculated from the current LoRa TX settings.

RF Transmission and Reception

Command	Description	Example
AT+RF_TX_HEX	Transmit data in HEX format	AT+RF_TX_HEX=48656C6C6F
AT+RF_TX_TXT	Transmit data as text	AT+RF_TX_TXT=Hello
AT+RF_RX_TO_UART	Enable/disable RX to UART	AT+RF_RX_TO_UART=1
AT+RF_RX_FORMAT	RX data output format	AT+RF_RX_FORMAT=HEX

Received data is displayed automatically (if RX_TO_UART=1 (ON), =0 (OFF), ?

Received data output format:

+RX:5,48656C6C6F,RSSI:-45 Where 5 = number of received bytes, 48656C6C6F = packet itself, -45 = packet RSSI

Saved Packets and Periodic Transmission

One packet can be stored in the AT dongle (NVM memory), which can then be sent at any time or set for periodic transmission

Command	Description	Example
AT+RF_SAVE_PACKET	Save packet to memory	AT+RF_SAVE_PACKET=010203
AT+RF_TX_SAVED	Transmit saved packet once	AT+RF_TX_SAVED
AT+RF_TX_SAVED_REPEAT	Start/stop periodic TX	AT+RF_TX_SAVED_REPEAT=ON
AT+RF_TX_NVM_PERIOD	Set saved packet TX period	AT+RF_TX_NVM_PERIOD=1000
AT+RF_TX_PERIOD_STATUS	Current periodic TX status	AT+RF_TX_PERIOD_STATUS?

RF Test Commands

For various testing purposes, these 3 commands may be useful, especially AT+RF_TX_CW=1 (ON), =0 (OFF), ?, which enables carrier wave transmission (no modulated data).

Command	Description	Example
AT+RF_TX_CW	Enable/disable CW (continuous wave) transmission	AT+RF_TX_CW=1
AT+RF_GET_TOA	Calculate Time on Air from current TX settings, parameter is packet length in bytes	AT+RF_GET_TOA=10
AT+RF_GET_TSYM	Get symbol time from current TX settings	AT+RF_GET_TSYM

AUX GPIO Pins (1-8)

Command	Description	Example
AT+AUX	Set pin state	AT+AUX=1,1 (pin 1 HIGH)
AT+AUX_PULSE	Start PWM	AT+AUX_PULSE=1,1000,50 (pin 1, 1Hz, duty 50%)
AT+AUX_PULSE_STOP	Stop PWM	AT+AUX_PULSE_STOP=1 (stop PWM on pin 1)

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Practical Usage Examples

Example 1: Simple Point-to-Point Communication

Dongle 1 (transmitter):

AT+LR_TX_SET=SF:9,BW:7,CR:45,Freq:869525000,IQInv:0,HeaderMode:0,CRC:1,Preamble:8,Power:22,LDRO:2 AT+RF_TX_HEX=AABBCCDD

Dongle 2 (receiver):

AT+LR_RX_SET=SF:9,BW:7,CR:45,Freq:869525000,IQInv:0,HeaderMode:0,CRC:1,Preamble:8,LDRO:2

→ Receiver will output: +RX:4,AABBCCDD,RSSI:-47

Example 2: Range Test with Periodic Transmission

TX Dongle: AT+LR_TX_SET=SF:12,BW:7,CR:45,Freq:869525000,IQInv:0,HeaderMode:0,CRC:1,Preamble:8,LDRO:2,Power:22 AT+RF_SAVE_PACKET=31313232333334343535 AT+RF_TX_NVM_PERIOD=2000 AT+RF_TX_SAVED_REPEAT=ON

RX Dongle: AT+LR_RX_SET=SF:12,BW:7,CR:45,Freq:869525000,IQInv:0,HeaderMode:0,CRC:1,Preamble:8,LDRO:2 AT+RF_RX_TO_UART=1 AT+RF_RX_FORMAT=ASCII

Subsequent RX reception: +RX:5,1122334455,RSSI:-68

Example 3: CW Test on Frequency

AT+LR_TX_FREQ=868000000 AT+LR_TX_POWER=10 AT+RF_TX_CW=1 Transmits carrier wave at 868 MHz with 10 dBm power

Stop TX: AT+RF_TX_CW=0

Example 4: Baud Rate Change

Query current speed: AT+UART_BAUD? 115200

Change to faster: AT+UART_BAUD=230400 OK Dongle restarts and switches to 230400 baud. Terminal must also be switched.

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Important Notes

TX/RX Parameter Compatibility

For successful communication, RF settings must match:

• Frequency (TXFREQ = RXFREQ)
• Spreading Factor (TXSF = RXSF)
• Bandwidth (TXBW = RXBW)
• Coding Rate (TXCR = RXCR)
• Sync Word (TXSYNCWORD = RXSYNCWORD)
• Header Mode (TXHEADERMODE = RXHEADERMODE)
• CRC (TXCRC = RXCRC)
• LDRO (LDRO 2 = automatic mode)
• IQInv (TXIQInv = RXIQInv)

Range vs. Speed Optimization

Maximum range (lowest speed): High SF and low BW → maximum range → slowest data rate

• SF: 12
• BW: 0 (7.81 kHz)
• CR: 48 (4/8)
• Power: 22 dBm
• → Range: > 10 km (open space)

High speed (shorter range):

• SF: 5
• BW: 9 (500 kHz)
• CR: 45 (4/5)
• Power: 22 dBm

Time on Air (ToA)

The higher the SF and lower the BW, the longer the transmission time. Use AT+RF_GET_TOA to get packet time on air.

Implicit vs. Explicit Header

• Explicit (0): Header contains packet length
• Implicit (1): No header - RX_PLDLEN must be set on receiver side before starting reception!

LDRO (Low Data Rate Optimization)

• Auto (2): Firmware automatically selects based on SF and BW - recommended
• On (1): Manually enabled - you can experiment and select suitable option for your settings
• Off (0): Manually disabled

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Troubleshooting

Dongle is not responding to AT commands

1. Check baud rate (try 115200 or 230400) 2. Check connection jumpers on serial line MCU-USB must be connected on both RX and TX headers 3. Check line ending (must be CR+LF) 4. Restart dongle (disconnect and reconnect USB) 5. Try AT+SYS_RESTART

RX not seeing TX data

1. Verify all RF parameters for TX and RX are identical 2. Verify RX has enabled AT+RF_RX_TO_UART=1 3. Increase TX power or shorten distance

Low RSSI or Packet Loss

1. Increase TX power (max 22 dBm) 2. Reduce distance 3. Try higher SF (7→9→12) 4. Try connecting external antenna - need to resolder jumper (zero ohm resistor in 0402 package) from chip antenna to UFL connector!!

CRC Errors

1. RF interference - change frequency 2. TX/RX parameter mismatch 3. Set LDRO to "auto" on both TX and RX sides

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Technical Specifications

Hardware

• MCU: STM32L071 (ARM Cortex-M0+)
• RF chip: Semtech SX1262
• Frequency: 150 MHz - 960 MHz
• TX power: 0 to +22 dBm
• RX sensitivity: up to -149.1 dBm (SF12, BW 7.81 kHz)
• USB: Virtual COM port
• GPIO: 8x AUX pins (PWM capable)

Operating Conditions

• Power supply: 5V from USB
• Temperature: -20°C to +70°C (operating)

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