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4G (Cellular) Switchover


In the previous topic, we explored the Wi-Fi interface and how your device can be configured to automatically switch over to Wi-Fi if the Ethernet link is unavailable. In addition to Ethernet and Wi-Fi, TPS devices support 4G communications. This project uses the LTE Tibbit (#45) as a backup way to send data to the MQTT server when the Ethernet connection goes down.


Note: The AppBlocks Demo Kit (ADK) does not contain Tibbit #45. You'll need to obtain this Tibbit separately if you wish to test this project.

4G is enabled on the Cellular page of the Features tab:


As with Wi-Fi, AppBlocks treats cellular as an alternative interface that will only be used if Ethernet -- the system's preferred interface -- becomes unavailable. Therefore, you must unplug the Ethernet cable to see the application switch to the 4G connection. As soon as the cable is plugged back in, the application will resume using the Ethernet interface.

Unlike with Wi-Fi, the system does not enable the 4G connection until it is actually needed. This is because sending and receiving data over 4G costs money, and there is always some traffic over 4G links, even when your system is not sending anything meaningful. To avoid wasting your funds, 4G only gets going after the Ethernet link fails and is shut down as soon as the Ethernet link is restored.

This project runs with Wi-Fi disabled, but you can enable it by yourself to see the switchover between all three interfaces:

  • The Ethernet is the preferred interface. The Wi-Fi interface will be unused (but associated with the access point) whenever there is an Ethernet link. 4G will be disabled.
  • If the Ethernet link goes down, the application will attempt to use Wi-Fi.
  • If it is impossible to associate with an access point, 4G communications will be attempted.

4G LED Patterns

As with Wi-Fi, TPS uses the five blue LEDs to tell you about the status of your 4G connection.

When the 4G interface is in the process of linking up to the cellular network, the following dynamic pattern plays on the LEDs:

4G signals -- connecting

When the link is established, you will see this static pattern:

4G signals -- connected