Continuous wave on SX1276

Question

I'm trying to send CW (like hello world) with the SX1278 on ttgo t-beam. I've read the datasheet and some examples and come to this code:

  sx1278my.writeRegister(REG_OP_MODE, FSK_SLEEP_MODE);
  sx1278my.writeRegister(REG_OP_MODE, FSK_STANDBY_MODE);  
  //433500000MHz
  sx1278my.writeRegister(REG_FRF_MSB, 0x6c);
  sx1278my.writeRegister(REG_FRF_MID, 0x60);
  sx1278my.writeRegister(REG_FRF_LSB, 0x00);  
  delay(10);

  sx1278my.writeRegister(REG_DIOMAPPING1, 0x00 );
  sx1278my.writeRegister(REG_FDEVMSB, 0x00);
  sx1278my.writeRegister(REG_FDEVLSB, 0x00);
  sx1278my.writeRegister(REG_BITRATEMSB, 0x00);
  sx1278my.writeRegister(REG_BITRATELSB, 0x00);

  sx1278my.writeRegister(REG_PACKETCONFIG1, 0x80); //variable length
  sx1278my.writeRegister(REG_PACKETCONFIG2, 0x00);

  // Disable radio interrupts
  sx1278my.writeRegister(REG_DIO_MAPPING1, 0x00);
  delay(10);
  //sx1278my.writeRegister(REG_OP_MODE, 0x00100011); //continuous mode, TX
  sx1278my.writeRegister(REG_OP_MODE, 0b00100011);

AFAIK it shall transmit now, however it does not. The Serial.print("REG_OP_MODE:"); Serial.println(sx1278my.readRegister(REG_OP_MODE), HEX); gives 0x01 which is stadby mode. gives 0x23 but no carrier is to be seen with rtl_sdr&gqrx. Any tips?

Answer 1

While I don't have any experience with this particular device, I can offer some basic guidance when dealing with a new device. You want to make sure that your read and write function calls are working properly. In the spirit of divide-and-conquer, the goal is to determine if the problem is due to the communication or due to unexpected behavior in the device.

I suggest that you first verify that you can reliably write to the device by putting a readRegister call after each writeRegister and comparing the read and write values.

In this specific case, your last line of code is:

sx1278my.writeRegister(REG_OP_MODE, 0x00100011); //continuous mode, TX

You're attempting to write a 32 bit value to an 8 bit register. Did you mean to write:

sx1278my.writeRegister(REG_OP_MODE, 0x23); //continuous mode, TX

Answer 2

Ok, for a reason I don't understand The PaSelect bit(7) in REG_PA_CONFIG has to be set:

sx1278my.writeRegister(REG_PA_CONFIG, 0b10100000);