SX1278 LoRa (Ra-02) with Arduino Nano — 433 MHz link with level shifting

LoRa sends small messages over kilometres on a few milliamps — farm sensors, water-tank levels across a colony, or a gate alarm at the far end of a plot. The Ra-02 (SX1278, 433 MHz) is the common module in India.

It is a 3.3 V part with SPI pins that must not see 5 V, so on the Nano it needs a 3.3 V regulator and a 4-channel level shifter. The same sketch runs on both boards: one sends “hello n” every 5 seconds, the other prints each packet with signal strength.

Wiring

Also needed: AMS1117 3.3 V regulator module, 4-channel BSS138 level shifter, 433 MHz antenna (a 17.3 cm wire works for testing), Ra-02 breakout/adapter board (the module has 2 mm pads).

Every connection
Arduino Nano	SX1278 LoRa module (Ra-02, 433 MHz)	Wire	Notes
AMS1117 3.3 V module (IN from Nano 5V) · 3.3V	3.3V	red	About 120 mA peaks while sending — too much for the Nano’s 3V3 pin. Module IN → Nano 5V, GND → Nano GND.
GND	GND	black
D10	NSS	purple	Via level shifter
D13	SCK	yellow	Via level shifter
D11	MOSI	green	Via level shifter
D12	MISO	blue	3.3 V output — the Nano reads it directly.
D9	RST	orange	Via level shifter — Shifter LV = 3.3 V from the regulator, HV = Nano 5V.
D2	DIO0	cyan	Interrupt output from the module, 3.3 V — direct.

3.3 V only (1.8–3.7 V) part, 5 V board. The SX1278 is a 3.3 V part and its pins are not 5 V tolerant. ESP32 and Pico connect directly. With an Uno or Nano, level-shift NSS, SCK, MOSI and RST, and power the module from a 3.3 V regulator that can supply about 120 mA while transmitting.

Board quirks

The SX1278 is not 5 V tolerant. NSS, SCK, MOSI and RST from the Nano must go through a level shifter; outputs (MISO, DIO0) can go direct.
BSS138 shifters are slow, so the sketch drops SPI to 1 MHz with LoRa.setSPIFrequency(1E6). At the default 8 MHz, begin() often fails.
Never transmit without an antenna — it can damage the RF stage.
433.05–434.79 MHz is licence-free in India for low-power devices; the sketch sets 10 dBm. Check the current WPC rules before increasing power.
Upload the same sketch to both Nanos, with IS_SENDER = false on the receiver. Both must use the same frequency and spreading factor.

Code

lora-nano.inoArduino C++Open in Playground Flash

// SX1278 (Ra-02, 433 MHz) LoRa on an Arduino Nano — same sketch for sender and receiver.
// 3.3V ← 3.3 V regulator, GND → GND, NSS ← D10, SCK ← D13, MOSI ← D11, RST ← D9 (all four through
// a level shifter), MISO → D12 and DIO0 → D2 direct. Set IS_SENDER = false on the second Nano.
#include <SPI.h>
#include <LoRa.h>

const bool IS_SENDER = true;
const long FREQ = 433E6;  // 433.05-434.79 MHz is the low-power licence-free band in India

void setup() {
  Serial.begin(115200);
  LoRa.setPins(10, 9, 2);       // NSS, RST, DIO0
  LoRa.setSPIFrequency(1E6);    // BSS138 shifters are slow; 1 MHz is plenty for LoRa
  if (!LoRa.begin(FREQ)) {
    Serial.println(F("LoRa init failed - check 3.3V, shifter and NSS/RST wiring"));
    for (;;) {}
  }
  LoRa.setTxPower(10);          // 10 dBm = 10 mW
  LoRa.setSpreadingFactor(9);   // longer range than the default SF7, slower
  Serial.println(IS_SENDER ? F("LoRa sender ready") : F("LoRa receiver ready"));
}

void loop() {
  if (IS_SENDER) {
    static unsigned int n = 0;
    LoRa.beginPacket();
    LoRa.print(F("hello "));
    LoRa.print(n);
    LoRa.endPacket();
    Serial.print(F("Sent packet "));
    Serial.println(n++);
    delay(5000);
  } else {
    int size = LoRa.parsePacket();
    if (size) {
      Serial.print(F("Received '"));
      while (LoRa.available()) Serial.print((char)LoRa.read());
      Serial.print(F("'  RSSI "));
      Serial.print(LoRa.packetRssi());
      Serial.print(F(" dBm  SNR "));
      Serial.println(LoRa.packetSnr(), 1);
    }
  }
}

// SX1278 (Ra-02, 433 MHz) LoRa on an Arduino Nano — same sketch for sender and receiver.
// 3.3V ← 3.3 V regulator, GND → GND, NSS ← D10, SCK ← D13, MOSI ← D11, RST ← D9 (all four through
// a level shifter), MISO → D12 and DIO0 → D2 direct. Set IS_SENDER = false on the second Nano.
#include <SPI.h>
#include <LoRa.h>

const bool IS_SENDER = true;
const long FREQ = 433E6;  // 433.05-434.79 MHz is the low-power licence-free band in India

void setup() {
  Serial.begin(115200);
  LoRa.setPins(10, 9, 2);       // NSS, RST, DIO0
  LoRa.setSPIFrequency(1E6);    // BSS138 shifters are slow; 1 MHz is plenty for LoRa
  if (!LoRa.begin(FREQ)) {
    Serial.println(F("LoRa init failed - check 3.3V, shifter and NSS/RST wiring"));
    for (;;) {}
  }
  LoRa.setTxPower(10);          // 10 dBm = 10 mW
  LoRa.setSpreadingFactor(9);   // longer range than the default SF7, slower
  Serial.println(IS_SENDER ? F("LoRa sender ready") : F("LoRa receiver ready"));
}

void loop() {
  if (IS_SENDER) {
    static unsigned int n = 0;
    LoRa.beginPacket();
    LoRa.print(F("hello "));
    LoRa.print(n);
    LoRa.endPacket();
    Serial.print(F("Sent packet "));
    Serial.println(n++);
    delay(5000);
  } else {
    int size = LoRa.parsePacket();
    if (size) {
      Serial.print(F("Received '"));
      while (LoRa.available()) Serial.print((char)LoRa.read());
      Serial.print(F("'  RSSI "));
      Serial.print(LoRa.packetRssi());
      Serial.print(F(" dBm  SNR "));
      Serial.println(LoRa.packetSnr(), 1);
    }
  }
}

Library: LoRa (Sandeep Mistry) — compiled with LoRa 0.8.0.

Expected serial output

Serial Monitor · 115200Output

LoRa receiver ready
Received 'hello 0'  RSSI -47 dBm  SNR 9.8
Received 'hello 1'  RSSI -48 dBm  SNR 10.0

LoRa receiver ready
Received 'hello 0'  RSSI -47 dBm  SNR 9.8
Received 'hello 1'  RSSI -48 dBm  SNR 10.0

Common errors

LoRa init failed

No 3.3 V, NSS/RST on the wrong pins, or SPI too fast through the shifter. Check wiring and keep setSPIFrequency(1E6).

Sender works, receiver hears nothing

Different frequency or spreading factor, DIO0 not wired, or no antenna on one side.