The aim of this project is to learn more about interacting with sensors. I'm using Nerves which is a Framework, Tooling and Platform built in Elixir, which enables you to get up and running with IoT projects pretty quickly. It handles things like networking, creating a build for different devices, being able to update firmware.
I'm using a Bosch BME280 pressure/temp/humidity sensor with a Raspberry Pi Zero. With this library built by Frank Hunleth https://github.com/fhunleth/bmp280.
Outcomes:
- UI displaying latest temperature readings.
- Read and write temp data to device
- Trigger a GPIO port on and off based off a max temp being reached.
TODO:
Update to use InfluxDB to persist data and use graph to visualise.Use pubsub instead of reading data at intervals.- Update UI styling
- Add ability to update max temp, currently hardcoded.
This project uses Phoenix Live View to display the temperature readings.
There are 2 processes that start up when the devices boots. 1 process handles reading from the sensor. The other process reads and writes the data to memory. To manage the data, currently temperatures are saved in memory to a queue, with a naive retention policy based on the number of items in the queue.
I'm using 2 GenServers (https://hexdocs.pm/elixir/GenServer.html) (sensor.ex, sensor_data.ex) to manage these processes.
The UI is handled using Phoenix LiveView. As i'm using live view we get a metrics dashboard for free. There is a link to this at the top of the UI, the dashboard will display things like current processes currently running on the device.
Currently temperatures are read from the sensor at 5 second intervals. A call to SensorData.add_data, which handles adding the temp data to a queue stored in memory. This function also uses Phoenix PubSub to broadcast the updated queue to any modules subscribed to the "sensor_reading" topic.
The view will read data from the memory in intervals and display as a list in the UI.
The live view is subscribed to this topic, so when the temp data is received, it updates the socket with the updated queue and the live view will update.
InfluxDB is used to persist the data and visualise, i'm running this locally on my laptop.
The sensor data is used to determine whether to trigger a GPIO port on or off, which port could be connected to a Solid State Relay which would trigger a heating/cooling element to be turned on or off. In this example i'm using an LED to indicate the port being triggered. There is a max temp of 21 hardcoded for now, when this temp is reached, the port is off, if under the port turns on.
Below is the hardware i'm using for this project. Any type of header can be used, i'm using a hammer header so I don't need to solder anything to the Pi Zero.
- Raspberry Pi Zero/Raspberry Pi Zero W
- Pi Zero Hammer Header
- BME280 Temperature sensor or BMP280 Temperature Sensor
- Red LED
- 330 ohm resistor
- Breadboard
- 6 male jumper cables
- Pi 3V3 to sensor VIN
- Pi GND to sensor GND
- Pi SCL to sensor SCK
- Pi SDA to sensor SDI
This app will trigger GPIO port 18. The below image is an example. Ensure to plug the positive wiring to GPIO port 18.
To set up locally follow these instructions https://docs.influxdata.com/influxdb/v2.0/get-started/.
- Start influxDB by running
influxd. - Go to
localhost:8086 - Follow these instructions https://docs.influxdata.com/influxdb/v2.0/get-started/#set-up-influxdb-through-the-ui
-
Setup InfluxDB (see instructions above)
-
Connect your Raspberry Pi Zero to your laptop via usb cable.
-
Prepare your Phoenix project to build JavaScript and CSS assets:
# These steps only need to be done once. cd ui mix deps.get npm install --prefix assets
-
Build your assets and prepare them for deployment to the firmware:
# Still in ui directory from the prior step. # These steps need to be repeated when you change JS or CSS files. npm install --prefix assets --production npm run deploy --prefix assets mix phx.digest
-
Change to the
firmwareapp directorycd ../firmware -
Create a .env file and add the below variables with your own values. See below for influxDB setup for the influx db variables.
export NERVES_NETWORK_SSID= export NERVES_NETWORK_PSK= export MIX_TARGET=rpi0 export INFLUX_TOKEN= export LOCAL_HOST_IP= export INFLUX_ORG= export INFLUX_BUCKET=
-
Get dependencies, source env file, build firmware, and burn it to an SD card:
mix deps.get source .env mix firmware mix firmware.burn -
Insert the SD card into your Raspberry Pi board and connect the USB cable or otherwise power it on.
-
In your terminal ping nerves.local to see when it has finished booting. (approx 5 - 10 secs)
-
Wait for it to finish booting (5-10 seconds)
-
Open a browser window on your host computer to
http://nerves.local/ -
You should see a screen displaying timestamps and temperature readings.
-
When temperature is below 21, LED will be triggered on. When temperature is above 21, LED is off.
-
Go to
localhost:8086to view InfluxDB UI and setup a query in the explorer. See here for how to run a query https://docs.influxdata.com/influxdb/v2.0/query-data/execute-queries/data-explorer/
If your device is pingable but you are not seeing anything in the browser window. You can try the below steps.
-
Open an iex session from the device.
In your terminal run
ssh nerves.local
-
This will open an iex session. Nerves provides RingLogger which enables us to view the logs from the device.
To see print all the messages from the log, run
RingLogger.nextTo monitor logs, run
RingLogger.attachIf there is an issue with reading from the sensor, the below error will display. If you receive this error, one thing you can try is to double check your wiring.
** (MatchError) no match of right hand side value: {:error, :i2c_nak}
(bmp280 0.2.2) lib/bmp280.ex:191: BMP280.query_sensor/1
(bmp280 0.2.2) lib/bmp280.ex:136: BMP280.handle_continue/2
(stdlib 3.13.2) gen_server.erl:680: :gen_server.try_dispatch/4
(stdlib 3.13.2) gen_server.erl:431: :gen_server.loop/7
(stdlib 3.13.2) proc_lib.erl:226: :proc_lib.init_p_do_apply/3