LoRa module not working with ESP32-C3's SPI interface

Community
1

I have wired a LoRa module (SX1278) with the ESP32C3.

The LoRa module uses the SPI interface to communicate with the ESP32C3.

When I connect all the SPI pins to the C3, the sketch seems to stop executing.

If I remove the MISO wire and reboot, the sketch executes, but the LoRa module is not recognized.

I have checked the SPI pin assignments (MOSI, MISO, SCK, SS) and they are all okay.

If I connect the LoRa module to my ESP32-WROOM dev kit, it works perfectly.

Not sure what to do next to diagnose the problem.

Any help would be greatly appreciated.

Regards,
Anand.

2

The problem is something to do with the way the ESP32C3 reads various pins at startup, with a bare bones SX127X in circuit the ESP32 goes into waiting for USB upload mode.

Fit pullup resistors to the LoRa devices NSS and SCK pins cures the problem for me.

3

The problem seems to be that the SX1278 pulls down the MISO pin on startup. The MISO / D9 pin is used to put the ESP32C3 into BOOT mode, which is why the ESP32C3 gets stuck!
As @StuartsProject suggests, adding a pullup resistor on NSS solves the issue (NSS = high deactivates the SX1278 module).

4

I fixed it by reassigning the SPI pins:

#include <SPI.h>

SPIClass spiCustom(HSPI);

...

spiCustom.begin(/* SCK  = */ 6, 
                    /* MISO = */ 7, 
                    /* MOSI = */ 21, 
                    /* SS   = */ 2);
    // Init SPI
    SPI.begin();
1 Like
5

Dear Anand,
I created a dedicated function for setting up the LoRa SX1278, and it seems to have solved the issue. Additionally, it does not require a pull-up resistor. Below is the code I used for an ESP32-C3 SuperMini as a receiver.

#include <SPI.h>
#include <LoRa.h>

#define SS 7     // Pino NSS (CS)
#define RST 3    // Pino de Reset
#define DIO0 1   // Pino de interrupção

/*
ESP 32 C3 / RA-01 SX1278

SCK   -> 4
MISO  -> 5
MOSI  -> 6
SS    -> 7
RST   -> 3
DIO0  -> 1
VCC   -> 3V3
GND   -> GND

*/

long BAND = 433E6; 

void loraSetup(){
  Serial.println("Inicializando LoRa...");

  SPI.begin(4, 5, 6, 7);  // SCK, MISO, MOSI, SS
 
  LoRa.setPins(SS, RST, DIO0);
  
  
  if (!LoRa.begin(BAND)) { // FrequĂȘncia do LoRa (433 MHz ou 915E6 para 915 MHz)
    Serial.println("Erro ao iniciar LoRa!");
    while (1);
  }
  LoRa.receive();
  Serial.println("LoRa iniciado com sucesso!");
}

void setup() {
  Serial.begin(115200);
  delay(500);  // Pequeno atraso para garantir inicialização correta

  loraSetup();
}

void loop() {
  // Verifica se hĂĄ um pacote LoRa disponĂ­vel
  int packetSize = LoRa.parsePacket();
  if (packetSize) { 
    Serial.print("Pacote recebido: ");

    String receivedData = "";
    
    while (LoRa.available()) {
      receivedData += (char)LoRa.read();  // LĂȘ o pacote corretamente como string
    }

    Serial.println(receivedData);
  }

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