BTHome ESP Arduino BLE

[sjmtlewy]

I was struggling to get the BTHome ESP32 example working on an ESP32-C6. This is because for newer ESP32 mcus there is a conflict between the Arduino-NimBLE library this is based on and changes that have been made by espressif. I've changed the example to use the ArduinoBLE library that is supplied with esp32-arduino. If this is of any help to anyone else, the meat of it is:

void BTHome::buildPaket() {
  //the Object ids have to be applied in numerical order (from low to high)
  if (this->m_sortEnable) sortSensorData();

  std::string serviceData = "";
  uint8_t i;

  // The encryption
  if (this->m_encryptEnable) {
    if (this->m_triggerdevice)
      serviceData += ENCRYPT_TRIGGER_BASE;
    else
      serviceData += ENCRYPT;

    uint8_t ciphertext[BLE_ADVERT_MAX_LEN];
    uint8_t encryptionTag[MIC_LEN];
    //buildNonce
    uint8_t nonce[NONCE_LEN];
    uint8_t* countPtr = (uint8_t*)(&this->m_encryptCount);
    esp_bd_addr_t* addrs = BLEDevice::getAddress().getNative();
    nonce[0] = *addrs[5];
    nonce[1] = *addrs[4];
    nonce[2] = *addrs[3];
    nonce[3] = *addrs[2];
    nonce[4] = *addrs[1];
    nonce[5] = *addrs[0];
    //esp_read_mac(&nonce[0], ESP_MAC_BT);
    nonce[6] = UUID1;
    nonce[7] = UUID2;
    nonce[8] = ENCRYPT;
    memcpy(&nonce[9], countPtr, 4);
    //encrypt sensorData
    mbedtls_ccm_encrypt_and_tag(&this->m_encryptCTX, this->m_sensorDataIdx, nonce, NONCE_LEN, 0, 0,
                                &this->m_sensorData[0], &ciphertext[0], encryptionTag,
                                MIC_LEN);
    for (i = 0; i < this->m_sensorDataIdx; i++) {
      serviceData += ciphertext[i];
    }
    //writeCounter
    serviceData += nonce[9];
    serviceData += nonce[10];
    serviceData += nonce[11];
    serviceData += nonce[12];
    this->m_encryptCount++;
    //writeMIC
    serviceData += encryptionTag[0];
    serviceData += encryptionTag[1];
    serviceData += encryptionTag[2];
    serviceData += encryptionTag[3];
  } else {
    if (this->m_triggerdevice)
      serviceData += NO_ENCRYPT_TRIGGER_BASE;
    else
      serviceData += NO_ENCRYPT;
    for (i = 0; i < this->m_sensorDataIdx; i++) {
      serviceData += this->m_sensorData[i];  // Add the sensor data to the Service Data
    }
  }

  BLEAdvertisementData advertisementData = BLEAdvertisementData();
  advertisementData.setFlags(ESP_BLE_ADV_FLAG_GEN_DISC | ESP_BLE_ADV_FLAG_BREDR_NOT_SPT);

  BLEUUID btHomeID((uint16_t)0xFCD2);

  advertisementData.setServiceData(btHomeID, String(serviceData.c_str(), serviceData.length()));

  if (!this->dev_name.isEmpty()) {
    int dn_length = this->dev_name.length() + 1;
    if (dn_length > 28) dn_length = 28;  //BLE_ADVERT_MAX_LEN - FLAG = 31 - 3
    advertisementData.setName(this->dev_name.substring(0, dn_length - 1));
  }
  pAdvertising->setAdvertisementData(advertisementData);
  pAdvertising->setAdvertisementType(ADV_TYPE_NONCONN_IND);
}

[RobWilks]

Thanks for sharing the adaptation for ArduinoBLE. How well has this worked for you?

I am trying to implement BTHome on an old esp32 development board (DOIT ESP32 DEVKIT V1)
However Chreece's code is not compatible with the most recent version of the NimBLE library.
I was wondering whether your approach might work for me. The alternative is to update Chreece's code to make it compatible with the most recent version of NimBLE - there seems to be a comprehensive migration log.

Any views on which route will be easier?

Cheers

RobWilks

[sjmtlewy]

Either route is fairly straightforward, or you could just use the old version of the NimBLE library if you just want it working quickly.

[Chreece]

@RobWilks you could check the updated code, I just merged a PR that should should be compatible with the latest NimBLE.
Please give some feedback if not, to revert the changes.

[RobWilks]

@Chreece thanks for the quick reply and even better for proposing a solution. I'll try it out and come back to you

[RobWilks]

The updated code worked perfectly with:
board: DOIT ESP32 DEVKIT V1
Arduino IDE
The DIY sensor appeared automatically in HA as expected

It is discoverable but not possible to connect to it with nRF Connect - not sure why - not important

Thankyou for the hard work on this. Possibly worth advertising to the HA community which has several people interested in making ESP BT Nodes

[sjmtlewy]

That's as-designed, as BTHome just uses advertisements not connections. It's good for battery-powered devices, which won't get their power drained by active scanning.

[RobWilks]

@sjmtlewy thanks for commenting. I guess I should read a primer on BLE!