Sim7020

Project Sim7020
SIM7020 NB-IOT modem
Status	In progress
Contact	bertrik
Last Update	2021-04-03

What

This page is about the SIM7020 NB-IOT module.

I want to experiment with this kind of network connectivity for either a bat activity monitor or air quality monitoring (particulate matter). The t-mobile portal at http://portal.iot.t-mobile.nl is dead. Use the iotcreators portal.

Status:

• I can send data from the SIM7020 to the network
• I can receive the data from the network in my own application, using the webhook

Next steps:

• find an Arduino library for this
  • what things need to be configured? put these in EEPROM?
• think about encoding data
• start sending data!

Hardware

I wired it up like this:

Connections

SIM7020	USB serial	Remark
G	nc	looped to SIM7020-K
R	TXD
T	RXD
K	nc	looped to SIM7020-G
V	3V3
G	GND
S	DTR

Software

Network setup

See:

• https://docs.iotcreators.com/docs/general-settings for general network settings
• https://docs.iotcreators.com/docs/_-2-attach-to-nb-iot-network for specific AT-commands

Things that need to be configured for the network and the backend:

• network: band (8), operator (20416), APN (cdp.iot.t-mobile.nl)
• backend: UDP server ip (172.27.131.100) and port (15683)

Receiving data from the device

First of all, a comparison to how things work with TheThingsNetwork:

• TTN publishes incoming data using MQTT
• MQTT is a light-weight publish-subscribe framework that decouples producers of data from consumers of data. So for example you can easily have one producer (the node) and several consumers, for example a logger, a data handler, or even a 3rd party that does its own thing with the data.
• TTN runs its own MQTT server, so you don't have to. There's no need for setting up your own server, with a public facing ip address, a firewall, security policies, etc.
• MQTT distinguishes different types of message by different "topics", you can only access topics you are authorised to (your own). So for example, you can easily authorise someone to see device messages, but not allow device registration access.

In my opinion, a very good match to the nature of the messages in such a network.

NB-IOT uses a different approach, I think this is called a web-hook:

• In the t-mobile dashboard you configure an "endpoint". When data comes in, t-mobile pushes data towards that using a HTTP POST.
• The endpoint is your own server that has to be ready to ready to receive incoming data. You have to manage this server yourself w.r.t. security. If you want other parties to use the data, you'll also have to come up with your own solution to that.

So, not as smart as TTN does it, but still very powerful.

How I'm making this work:

• I have a service running on a specific port on a VPS, with a Java REST API behind it (based on jersey)
• I enter the URL of the service, including the port, into the iotcreators dashboard.

If the service is not actively running at that time, this will trigger an error message in the dashboard, but the URL is still accepted.

Incoming data received by HTTP POST looks like this:

{
  "reports": [
    {
      "serialNumber": "IMEI:868333030676163",
      "timestamp": 1615660679246,
      "subscriptionId": "06f872fc-02b3-4b20-8394-3f19a7006ca9",
      "resourcePath": "uplinkMsg/0/data",
      "value": "01a3021c"
    }
  ],
  "registrations": [],
  "deregistrations": [],
  "updates": [],
  "expirations": [],
  "responses": []
}

Data messages always have a report, with resourcepath set to "uplinkMsg/0/data".

Support in my LoraLuftdatenForwarder

I've added preliminary support for this, see: https://github.com/bertrik/LoraLuftdatenForwarder/tree/nbiot/LoraLuftdatenForwarder/src/main/java/nl/bertriksikken/nbiot

References

I followed roughly this guide:

• Ordered a SIM7020 and a starter kit, see https://www.hackster.io/voske65/arduino-nb-iot-with-sim7020-and-t-mobile-027f8f
• Regional settings for the network: https://docs.iotcreators.com/docs/general-settings
• t-mobile IOT configuration page: https://portal.iotcreators.com/ ?