Sim7020

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Revision as of 14:39, 24 January 2021 by Bertrik Sikken (talk | contribs)
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Project Sim7020
Sim7020.png
SIM7020 NB-IOT modem
Status In progress
Contact bertrik
Last Update 2021-01-24

What

This page is about the SIM7020 NB-IOT module.

I plan to experiment with this kind of network connectivity for perhaps a bat activity monitor or air quality monitoring.

Update: this escalated quickly ... the NB-IOT stuff at t-mobile already seems dead: Chromium complained about an expired certificate for the https website, otherwise seems down (error 503).

wget says:

bertrik@zenbook:~$ wget http://portal.iot.t-mobile.nl/
--2021-01-23 19:01:06--  http://portal.iot.t-mobile.nl/
Resolving portal.iot.t-mobile.nl (portal.iot.t-mobile.nl)... 52.57.78.255
Connecting to portal.iot.t-mobile.nl (portal.iot.t-mobile.nl)|52.57.78.255|:80... connected.
HTTP request sent, awaiting response... 503 Service Unavailable: Back-end server is at capacity
2021-01-23 19:01:06 ERROR 503: Service Unavailable: Back-end server is at capacity.

bertrik@zenbook:~$ wget https://portal.iot.t-mobile.nl/
--2021-01-23 19:02:35--  https://portal.iot.t-mobile.nl/
Resolving portal.iot.t-mobile.nl (portal.iot.t-mobile.nl)... 52.57.78.255
Connecting to portal.iot.t-mobile.nl (portal.iot.t-mobile.nl)|52.57.78.255|:443... connected.
ERROR: The certificate of ‘portal.iot.t-mobile.nl’ is not trusted.
ERROR: The certificate of ‘portal.iot.t-mobile.nl’ has expired.
The certificate has expired

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

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:

  • You configure an "endpoint" and t-mobile pushes data towards that
  • 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.

References

I followed roughly this guide: