Raspberry Pi temperature logger for Adafruit IO

RPiTemp is a simple proof-of-concept utility to post to Adafruit IO the readings from one or more DS18B20 temperature probes. It's intended for use on a Raspberry Pi.

It has one purpose: on an interval (2 minutes seems right), read the temperatures, and post them using the REST API for Adafruit IO.

Build and deploy steps

Format and lint Go code

goimports -w rpi_temp.go
golangci-lint run  --enable-all rpi_temp.go

Cross-compile for Raspberry Pi

Building a Go binary on the RPi is quite slow, but can be done. It's recommended to run the compilation on another computer, then copy just the executable to the RPi, with scp.

env GOARCH="arm" GOARM="6" GOOS="linux" go build rpi_temp.go

TODO(tedb): Convert to a build tool

Create Adafruit IO "feed"

Substitute each probe's serial number for 011850aaaaaa, from: cat /sys/bus/w1/devices/28-*/name

export ADAFRUIT_IO_KEY=zzzzzzzzz
export ADAFRUIT_USER=myusername
export SERIAL=011850aaaaaa

curl -X POST -H "Content-Type: application/json" -H "X-AIO-Key: $ADAFRUIT_IO_KEY" \
    --data '{"feed": {"name": "Temp $SERIAL"}}' \
    https://io.adafruit.com/api/v2/$ADAFRUIT_USER/feeds

Run on RPi

In the URL, %s will be substituted with the serial number of the 1-Wire probe.

export ADAFRUIT_IO_KEY=zzzzzzzzz
export ADAFRUIT_USER=myusername
export ADAFRUIT_IO_URL=https://io.adafruit.com/api/v2/$ADAFRUIT_USER/feeds/temp-%s/data
./rpi_temp

TODO(tedb): document running from systemd timer

Aren't there several other scripts and tools that do this?

Many scripts and tools are similar. But, this one is mine. :)

Apparently, writing a tool like this is a popular hobby. I didn't find a script that does this exact one thing: read the temperature an post it to Adafruit.IO. Some of them don't work with multiple temperature probes.

What's the back story?

After setting up a small fish tank, my first realization was it would be a perfect excuse to rig up an old otherwise-useless first-generation Raspberry Pi. Rigging up a fish-tank cam with some 1-Wire probes is pretty much the Hello World of RPi electronics tinkering. This is my idea of "a fun hobby".

Why Adafruit IO?

Adafruit has a fantastic focus on serving the individual hobby hacker for electronics components, microcontrollers, etc. I am primarily a software person, and over the years I've been grateful to have learned so much from Adafruit's hardware tutorials. There are places to get cheaper prices on parts, but it's worthwhile to know that Adafruit vets the things they sell, and that I can trust the parts are legitimate and will work as intended.

In a cunning move, they have launched an "internet of things" cloud service targeting my exact use case. I could also get started with the API immediately with zero fuss. The first prototype was just a Bash one-liner with curl.

What about the major cloud providers?

The major cloud providers (Google Cloud, AWS, Azure, etc.) all have big pushes into the "Internet of Things" space. Unfortunately, it was harder to figure out how to get started for my simple use case than I was willing to invest. Just setting up authentication for a device (with OAuth, certificates, etc.) is a bigger lift than the actual work to log the temperatures.

Goals?

This is part utilitarian tool, and part "art project": in that way, it is not unlike gardening. Potential future directions:

• Automatically build a binary for RPi using GitHub Actions
• Refactor the REST call to use the official Go client.
• Use MQTT client to post results
• Integration tests.
• On start-up, create data feeds as needed for the attached sensors. (MQTT group post automatically creates feeds)
• Provide systemd unit files
• Run the build (and dev tools like linting) with Bazel
• Provide Debian package, from Bazel
• Notify me (e.g. email, or Pushover) when the temp exceeds a range
• Maybe port the code to Elixir
• Consider "bulk read" interface (faster?)
• Capture RPi camera and publish to Adafruit for its dashboard; see docs