Drizzle is a Nerves-based home sprinkler system. It is designed to support up to 8 zones, and will automatically adjust watering times given local weather data. By default, the watering times will increase gradually as the temperature reaches a predetermined threshold (90ºF) and will decrease gradually based on recent and upcoming precipitation. The system will also shut down when the temperature drops below a predetermined threshold (40ºF). You also have the option to set "Winter months", which are months where the system will not run regardless of temperature.
Configuration
For the system to work properly, you need to export some ENV variables. For weather forecasts, set the following:
LATITUDE=<your local latitude>LONGITUDE=<your local longitude>DARKSKY_API_KEY=<your 32 character API key>Weather forecasts are retrieved from Dark Sky. You can get a free API key at: https://darksky.net/dev.
First boot
When your device starts up for its first time it will need to know the SSID and passphrase (aka PSK, pre-shared key) for the wireless SSID its going to connect to (for weather updates for example). This process is done using the VintageNetWizard, so this means you have to temporarily connect your mobile or laptop to the wireless access point named "nerves_xxxxx" (where xxxxx is an automatically generated ID for your nerves machine) and access a basic web portal to select your home network and provide its password.
Once you select a wireless network and provide the credentials, just double-check your entered the correct passphrase and click on Complete without validation button (as validation involves the AP dropping the connection to test connecting to your home router's AP and then reconnecting it back to the temporary AP later - so I find it error-prone and inconvenient).
After the process is complete, the WiFi card will be automatically configured with the SSID and passphrase upon next boot-ups.
The device is now discoverable as drizzle.local (try pinging it!) and exposes an SSH server into the Erlang VM console:
$ ping drizzle.local
PING drizzle.local (192.168.8.111) 56(84) bytes of data.
64 bytes from 192.168.8.111 (192.168.8.111): icmp_seq=1 ttl=64 time=12.2 ms
64 bytes from 192.168.8.111 (192.168.8.111): icmp_seq=2 ttl=64 time=6.41 ms
^C
--- drizzle.local ping statistics ---
2 packets transmitted, 2 received, 0% packet loss, time 1002ms
rtt min/avg/max/mdev = 6.407/9.304/12.201/2.897 ms
ekarak@ekarak-Latitude-7400:~$ ssh drizzle.local
The authenticity of host 'drizzle.local (192.168.8.111)' can't be established.
RSA key fingerprint is SHA256:s6rDEVL9YH3LaEDRxRX4qStknwY3560Vs5wkQ4wQMmA.
Are you sure you want to continue connecting (yes/no/[fingerprint])? yes
Warning: Permanently added 'drizzle.local' (RSA) to the list of known hosts.
Interactive Elixir (1.10.3) - press Ctrl+C to exit (type h() ENTER for help)
The Nerves.Runtime.Helpers have been removed. Use https://hex.pm/packages/toolshed instead.
iex(1)>
OTA firmware upgrades
Once you've pinged it succesfully you can leverage nerves_firmware_ssh mechanism to do OTA (over-the-air) firmware upgrades (so that you don't need to swap the microSD card in and out from your RPi), as follows:
# write out the firmware upload script (upload.sh), you only need this done once
$ mix firmware.gen.script
# generate firmware file
$ mix firmware
# run the upload script
$ ./upload.sh drizzle.local ./_build/rpi3/rpi3_dev/nerves/images/drizzle.fwHow It Works
- Starts the weather data agent, which stores state for the previous 12 hours and next 24 hours of weather. Until the system has been online for 12 hours, your previous 12 hours will not be set.
- Registers each of your zones with a corresponding GPIO pin on your device.
- Initializes a schedule of todays events. (This will happen at midnight each day or whenever the schedule for today is empty.) This means starting up a genserver and loading it with the schedule from your config file.
- Starts a recurring genserver that checks the weather each hour and updates the weather data agent.
- Each minute the scheduler checks if there is a scheduled event for the current time. Events are either to activate or deactivate a zone. If an event is scheduled, the GPIO sends the correct signal to the relay board to fulfill the request.
Targets
Nerves applications produce images for hardware targets based on the
MIX_TARGET environment variable. If MIX_TARGET is unset, mix builds an
image that runs on the host (e.g., your laptop). This is useful for executing
logic tests, running utilities, and debugging. Other targets are represented by
a short name like rpi3 that maps to a Nerves system image for that platform.
All of this logic is in the generated mix.exs and may be customized. For more
information about targets see:
https://hexdocs.pm/nerves/targets.html#content
Testing
Getting Circuits.GPIO to work in stub mode is tricky, as it needs recompilation. You only need to recompile when you switch mix targets though:
$ rm -rf _build/
$ MIX_ENV="test" MIX_TARGET="host" CIRCUITS_MIX_ENV="test" mix test
...when done with testing, clean all build artifacts and recompile:
$ rm -rf _build/
$ MIX_TARGET="rpi3" mix firmwareGetting Started
To start your Nerves app:
export MIX_TARGET=my_targetor prefix every command withMIX_TARGET=my_target. For example,MIX_TARGET=rpi3- Install dependencies with
mix deps.get - Create firmware with
mix firmware - Burn to an SD card with
mix firmware.burn
Learn more
- Official docs: https://hexdocs.pm/nerves/getting-started.html
- Official website: http://www.nerves-project.org/
- Discussion Slack elixir-lang #nerves (Invite)
- Source: https://github.com/nerves-project/nerves