Another LoRa Temperature/Humidity Sensor

Having deployed my Adafruit Feather version of a Temperature/Humidity LoRa Sensor to make use of my The Things Network gateway it’s now time to build another sesnor, this time with a Raspberry Pi Zero.

Pi Supply LoRa node pHat with sensor

I have a Pi Supply LoRa node pHAT that adds the radio side of things, but I needed a sensor. The pHAT has a header on the right hand edge which pulls out the 3.3v, 2, 3, 4 and Gnd, pins from the pi.

These just happen to line up with the I2C bus. They are also broken out in the same order as used by the Pimoroni Breakout Garden series of I2C sensors which is really useful.

Pimoroni’s Breakout Garden offer a huge range of sensors and output devices in either I2C or SPI. In this case I grabbed the BME680 which offers temperature, pressure, humidity and air quality in a single package.

Pimoroni supply a python library to read from the sensor so it was pretty easy to combine this with python to drive the LoRa pHat

#!/usr/bin/env python3
from rak811 import Mode, Rak811
import bme680
import time

lora = Rak811()
lora.hard_reset()
lora.mode = Mode.LoRaWan
lora.band = 'EU868'
lora.set_config(app_eui='xxxxxxxxxxxxx',
                app_key='xxxxxxxxxxxxxxxxxxxxxx')
lora.join_otaa()
lora.dr = 5

sensor = bme680.BME680(bme680.I2C_ADDR_PRIMARY)
sensor.set_humidity_oversample(bme680.OS_2X)
sensor.set_temperature_oversample(bme680.OS_8X)
sensor.set_filter(bme680.FILTER_SIZE_3)

while True:
    if sensor.get_sensor_data():
        temp = int(sensor.data.temperature * 100)
        humidity = int(sensor.data.humidity * 100)
        foo = "{0:04x}{1:04x}".format(temp,humidity)
        lora.send(bytes.fromhex(foo))
        time.sleep(20)

lora.close()

I’m only using the temperature and humidity values at the moment to help keep the payload compatible with the feather version so I can use a single “port” in the TTN app.

I’ve put all the code for both this and the Feather version on GitHub here.

As well as the Pi Zero version I’ve upgraded the Feather with a 1200mAh LiPo battery and updated the code to also transmit the battery voltage so I can track battery life and work out how often I need to charge it.

Adding the battery also meant I could stick it in my bag and go for a walk round the village to see what sort of range I’m getting.

I’m currently using a little coil antenna on the gateway that is laid on it’s side, I’ll find something to prop it up with which should help. The feather is also only using a length of wire antenna so this could be seen as a worst case test.

It’s more than good enough for what I need right now, but it would be good to put a proper high gain one in then it might be useful to more people. It would be great if there was a way to see how many unique TTN applications had forwarded data through a gateway to see if anybody else has used it.

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).

Adafruit Feather LoRa Module

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.

Plots of Temperature and Humdity

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.