T3-S3 LR1121 Quick Start

Required Libraries

Library	Version	Source
RadioLib	Latest	GitHub
U8g2	Latest	Arduino Library Manager

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Arduino

PlatformIO (Recommended)

1. Install VS Code with the PlatformIO IDE extension
2. Clone the repository:

   git clone https://github.com/Xinyuan-LilyGO/LilyGo-LoRa-Series.git

3. Open the project and select the T3-S3-LR1121 environment in platformio.ini
4. Click ✓ to build, connect via USB-C, then click → to upload

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Arduino IDE

Board Settings

Setting	Value
Board	LilyGo T3-S3
Board Revision	Radio-LR1121
Upload Speed	921600
USB Mode	Hardware CDC and JTAG
USB CDC On Boot	Enabled
CPU Frequency	240 MHz (WiFi)
Flash Mode	QIO 80 MHz
Flash Size	4MB (32Mb)
Partition Scheme	Default 4MB with spiffs
PSRAM	QSPI PSRAM

Steps

1. Install Arduino IDE and add ESP32 board support: https://espressif.github.io/arduino-esp32/package_esp32_index.json
2. Clone the LilyGo-LoRa-Series repo and open an example sketch
3. Set Board Revision to Radio-LR1121
4. Click Upload

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Peripheral Examples

LoRa (LR1121 tri-band)

#include <RadioLib.h>

// T3-S3 LR1121: CS=7, IRQ=33, RST=8, BUSY=34
LR1121 radio = new Module(7, 33, 8, 34);

void setup() {
  Serial.begin(115200);
  radio.reset();
  int state = radio.begin(915.0);
  if (state != RADIOLIB_ERR_NONE) {
    Serial.print("Radio init failed: "); Serial.println(state);
    while (true);
  }
  radio.setOutputPower(22);
  Serial.println("LR1121 ready");
}

void loop() {
  int state = radio.transmit("Hello LR1121");
  if (state == RADIOLIB_ERR_NONE) Serial.println("Sent OK");
  delay(2000);
}

OLED Display (SH1106 1.3-inch)

#include <U8g2lib.h>
#include <Wire.h>

// SH1106 128×64 I2C, SDA=18, SCL=17
U8G2_SH1106_128X64_NONAME_F_HW_I2C u8g2(U8G2_R0, U8X8_PIN_NONE);

void setup() {
  Wire.begin(18, 17);
  u8g2.begin();
}

void loop() {
  u8g2.clearBuffer();
  u8g2.setFont(u8g2_font_ncenB08_tr);
  u8g2.drawStr(0, 20, "LR1121 Ready");
  u8g2.sendBuffer();
  delay(1000);
}

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Notes

• LR1121 tri-band radio: Supports 400–520 MHz, 830–945 MHz, and 2400–2500 MHz; the board cannot TX and RX on two bands simultaneously
• 1.3-inch OLED: Larger than the 0.96-inch on most T3 siblings — initialize with the correct U8g2 display constructor
• RTC: PCF85063ATL is present on I2C — useful for low-power timestamped data logging
• PSRAM: QSPI PSRAM — select QSPI PSRAM in Arduino IDE

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FAQ

Q: LR1121 not responding? A: The LR1121 requires a reset pulse on startup. Call radio.reset() before radio.begin().

Q: Cannot upload? A: Ensure USB CDC On Boot is Enabled. Hold BOOT + press RST to enter download mode if needed.