rak8212-espruino-nb-iot

Prototyping NB-IoT devices with the RAK8212 (Quectel BG96) running Espruino

data-logger-bg96-mqtt.js

This example shows how one could use the MQTT stack already provided by the Quectel BG96. The advantage is that you don't need to care about the MQTT implementation on your own, e.g. by including the Espruino MQTT module. The disadvantage is, that possibly you may want to fine-tune things in the MQTT communication with your peer, and you can't. I think for almost all cases the Quectel MQTT stack should be sufficient and is a good starting point.

The example creates a NB-IoT connection with the radio network, and then creates a MQTT session with the MQTT server. It then publishes a temperature value every 60 seconds using MQTT.

Resilience

NB-IoT connections may break from time to time, the MQTT session may get terminated, publishing of messages may fail. The code uses a Finite State Machine, and in case of communication issues it shuts down the BG96 module and restarts. A "restarts" counter is reported to the AWS device shadow.

Memory usage

Low memory is an issue. It is recommended to switch on the minification feature of the Espruino Web IDE. This makes your code smaller before transferring it to the RAK8212.

Device shadow

The device shadow ("digital twin") representation in AWS IoT currently looks as follows:

{
  "desired": {
    "led": "off"
  },
  "reported": {
    "temperature": "26.47",
    "led": "off",
    "memory": {
      "free": 763,
      "usage": 1737,
      "total": 2500,
      "history": 389
    },
    "restarts": 0
  }
}

upload-ssl-certs-to-bg96.js

Some IoT Platforms (like AWS IoT) require the MQTT client to authenticate using a SSL client certificate. As the Quectel BG96 already has an embedded MQTT stack, one must supply the following files to enable authenticated and encrypted communication:

• The MQTT client's client certificate (e.g. 3a34634a38-certificate.pem.crt on AWS IoT)
• The private key of the client (e.g. 3a34634a38-private.pem.key)
• The trusted root CA certificates

All files have to be provided in PEM format. As this format is in ASCII, you can just cut and paste the contents to the JavaScript source code.

Then transfer the code to the device (using the Espruino IDE) and call function uploadCertificates(); The files will be saved to the device as cert.pem, key.pem and cacert.pem and can be used in a later step to configure the SSL connection options for the embedded MQTT stack.

data-logger-mqtt.js

This example uses the Espruino MQTT module as implementation for the MQTT protocol. The example provides a communication layer between this MQTT implementation and the BG96 which is purely used to send and receive data to/from the remote MQTT server. This communication layer only deals with IP communication. There was the need to introduce some queuing mechanisms, and MQTT ping/pong messages may interfere with other messages. My recommendation is not to use this example, as it is just to unstable and error-prone.