sensors – Ben's Place

Google Assistant Sensors

Having built my 2 different LoRA connected temperature/humidity sensors I was looking for something other than the Graphana instance that shows the trends.

Being able to ask Google Assistant the temperature in a room seemed like a good idea and an excuse to add the relatively new Sensor device type my Google Assistant Bridge for Node-RED.

I’m exposing 2 options for the Sensor to start with, Temperature and Humidity. I might look at adding Air Quality later.

Once the virtual device is setup, you can feed data in the Google Home Graph using a flow similar to the following

The join node is set to combine the 2 incoming MQTT messages into a single object based on their topics. The function node then builds the right payload to pass to the Google Home output node and finally it feeds it through an RBE node just to make sure we only send updates when the data changes.

msg.payload = {
  params: {
    temperatureAmbientCelsius: msg.payload["bedroom/temp"],
    humidityAmbientPercent: Math.round(msg.payload["bedroom/humidity"])
  }
}

LoRa Temperature/Humidity Sensor

After deploying the TTN Gateway in my loft last year, I’ve finally got round to deploying a sensor to make use of it.

As the great lock down of 2020 kicked off I stuck in a quick order with Pimoroni for a Adafruit Feather 32u4 with an onboard LoRa radio (In hindsight I probably should have got the M0 based board).

I already had a DHT22 temperature & humidity and the required resistor so it was just a case of soldering on an antenna of the right length and adding the headers so I could hook up the 3 wires needed to talk to the DHT22.

There is an example app included in with the TinyLoRa library that reads from the sensor and sends a message to TTN every 30 seconds.

(There are full instructions on how to set everything up on the Adafruit site here)

Now the messages are being published to TTN Application I needed a way to consume them. TTN have a set of Node-RED nodes which make this pretty simple. Though installing them did lead to a weekend adventure of having to upgrade my entire home automation system. The nodes wouldn’t build/install on Node-RED v0.16.0, NodeJS v6 and Raspbian Jessie so it was time to upgrade to Node-RED v1.0.4, NodeJS v12 and Raspbian Buster.

Node-RED flow consuming messages from Temp/Humidity sensor from TTN

This flow receives messages via MQTT direct from TTN, it then separates out the Temperature and Humidity values, runs them through smooth nodes to generate a rolling average of the last 20 values. This is needed because the DHT22 sensor is pretty noisy.

It outputs these smoothed values to 2 charts on a Node-RED Dashboard. which show the trend over the last 12 hours.

It also outputs to 2 MQTT topics that mapped to my public facing broker, which means they can be used to resurrect the temperature chart on my home page, and when I get an outdoor version of the sensor (hopefully solar/battery powered) up and running it will have both lines that my old weather station used to produce.

The last thing the flow does is to update the temperature reading for my virtual thermostat in the Google Assistant HomeGraph. This uses the RBE node to make sure that it only sends updates when the value actually changes.

The next step is to build a couple more and find a suitable battery and enclosure so I can stick one in the back garden.

Tinkerforge Node-RED nodes

For a recent project I’ve been working on a collection of different Node-RED nodes. Part of this set is a group of nodes to interact with Tinkerforge Bricks and Bricklets.

Tinkerforge is a platform of stackable devices and sensors/actuators that can be connected to via USB or can be attached directly to the network via Ethernet or Wifi.

Collections of sensors/actuators, known as bricklets, are grouped together round a Master Brick. Each Master Brick can host up to 4 sensors/actuators but multiple Master Brick’s can be stacked to add more capacity. The Master Brick also has a Micro USB socket which can be used to connect to a host machine running a deamon called brickd. The host runs a daemon that handles discovering the attached devices and exposes access to them via an API. There are also Ethernet (with and without PoE) and WiFi bricks which allow you to link the stack directly to the network.

As well as the Master Brick there is a RED Brick which contains a ARM Cortex A8 processor, SD card, USB socket and micro HDMI adapter. This runs a small Linux distribution (based on Debian) and hosts a copy of brickd.

There are bindings for the API in a number of languages including:

C/C++
C#
Delphi
Java
Javascript
PHP
Perl
Python
Ruby

For the Node-RED nodes I took the Javascript bindings and wrapped them as Node-RED nodes. So far the following bricklets are supported:

Adding others shouldn’t be hard, but these were the ones I had access to in order to test.

All the nodes share a config node which is configured to point to the instance of the brickd the sensors are linked and it then provides a filtered list of available bricklets for each node.

The code for the nodes can be found here and is available on npmjs.org here