IoT with Sub-1 GHz Sensor Network

The idea is to have a local network of sensors connected to a hub. Obviously, I'd like to interface those sensors with Node-RED, which offers native support for MQTT and JSON, with an off-the-shelf protocol I could rely on.

Candidates for the radio include WiFi, Bluetooth and sub-1 GHz. The low power requirement rules the WiFi solution out. Both Bluetooth and sub-1 GHz fit for the low volume of data transferred. However, Bluetooth has a limited range and do not cross walls. So the sub-1 GHz remains the recommended option.

However, sub-1 GHz doesn't include a TCP/IP stack, on which MQTT relies. Luckily, there are specific protocols for sensors, but they require a gateway so they can talk with the MQTT broker. One the MQTT side, there is a variant called MQTT-SN for sensor network.

Two Half-Failures

Texas Instruments has two evaluation kits with a gateway for sub-1 GHz sensors.

The first, the SimpleLink™ Sub-1 GHz Sensor to Cloud Gateway Reference Design for TI-RTOS Systems, uses a CC3220SF as a bridge between the sub-1 GHz sensors and a WiFi network with MQTT messages. Unfortunately, the provided solution was intended to run on IBM Bluemix, which has been passed out and is replaced by IBM Cloud.

Form left to right, the CC1310 LaunchPad with the Sensors BoosterPack, and the CC1350 LaunchPad used as a BoosterPack on top of the CC3220SF LaunchPad.

So I asked for help and get some pointers from the E2E forum. All the application notes were updated to release A and I was able to complete the

On the right, the web-page shows the connected CC1310 LaunchPad with the temperature.

However, I wasn't able to connect to IBM Cloud or to a local MQTT broker.

The second, the Sub-1 GHz Sensor to Cloud Industrial IoT Gateway Reference Design for Linux Systems, runs on a BeagleBone. A sub-1 GHz radio is plugged into the USB port and the BeagleBone runs the bridge to send MQTT messages. As before, the provided solution runs on AWS and the credentials required for the demo are not available for individuals.

Form left to right, the CC1350 SensorTag, the CC1350 LaunchPad connected through USB to the BeagleBone Black.

I failed to set the third-party services despite the instructions provided by Texas Instruments, and so I couldn't complete any of the demos.

So I asked for help and get some pointers from the E2E forum. Actually, there is a parallel application note with a procedure to set a 802.15.4 star network and run a web-service on a local machine.

On the right, the web-page shows two nodes, one CC1350 SensorTag and one CC1310 LaunchPad.

However, I wasn't able to figure out how to connect it to a MQTT broker.

One Success

So I turned to another solution based on the Moteino boards from LowPowerLab. The boards are very compact and combine a sub-1 GHz radio (433, 868 or 915 MHz) with an ATmega328.

The radios are provided by the modules RFM69 and RFM95/96 from HopeRF, based on the SX1231and SX127x transceivers from Semtech.

The boards come with an extensive suite of libraries, for radio, EEPROM, power management, OTA upload.

This solution relies on MQTT-SN, and comes with all the required examples prepared by Rodrigo Méndez.

There are two sketches, one for the nodes and another for the bridge. They run on the same Moteino boards.

The clients run the An example of an Aquila 2.0 MQTT-SN client implementation for RFM69.
The bridge is operated by the MQTT-SN Bridge firmware for RFM69 RF module and is plugged into an USB port of the Raspberry Pi.

Form left to right, the Moteino node, the Moteino gateway connected through USB to the Raspberry Pi.

The application for the gateway runs on the Raspberry Pi.

The gateway on the Raspberry Pi, is the MQTT-SN gateway for the Aquila 2.0 platform (actually the develop branch), which transfers the messages between the MQTT-SN bridge and the MQTT broker. It also acts as a port forwarder between the USB port the MQTT-SN bridge is connected to and the gateway.

Left: Monitoring the node
Click to enlarge

Right: Monitoring the bridge

Finally, I'm using mosquitto as the MQTT broker.

Node-RED connects to the MQTT broker, receives and displays the messages, and sends the commands.

A dashboard displays the messages and provides a switch button for easier interaction.

Conclusion

Despite all the buzz around IoT and home automation, I'm surprised to find a limited offer of solutions, and the instability of most of them. I've faced unexpected issues that lead to half-successes, with the Aquila and Moteino as a notable exception.

If home automation is the new main trend, there is ample room for easy-to-use and robust solutions.

I haven't tested other solutions like CoAP or ZigBee.