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Weather Lights

I recently spoke at the GitHub Patchwork event in Boulder last month. My son Nathan tagged along to get his first taste of the GitHub Flow. I don’t necessarily want him to be a programmer, but I do push him to learn a little to augment his interest in meteorology and astronomy.

The night was a success. He made it through the tutorial with only one complaint: the Patchwork credit went to my wife, who had created a GitHub login that night.

Since then, I’ve been looking for a project to continue his progress. I settled on a weather light, which consists of a ruby script that changes the color of a Philips Hue bulb. If you’re already an experienced coder, jump straight to the source at github.com/technoweenie/weatherhue.

NOTE: This post has been updated to match the latest version of the weatherhue script. You can still read the original blog post if you really want.


Unfortunately, there’s one hefty requirement: You need a Philips Hue light kit, which consists of a Hue bridge and a few lights. Once you have the kit, you’ll have to use the Hue API to create a user and figure out the ID of your light.

Next, you need to setup an account for the Weather2 API. There are a lot of services out there, but this one is free, supports JSON responses, and also gives simple forecasts. They allow 500 requests a day. If you set this script to run every 5 minutes, you’ll only use 288 requests.

After you’re done, you should have five values. Write these down somewhere.

Finally, you need ruby, with the following gems: faraday and dotenv. If you’re on a version of ruby lower than 1.9, you’ll also want the json gem.

Writing the script

I’m going to describe the process I used to write the weatherhue.rb script. Due to the way ruby runs, it’s not necessarily in the order that the code is written. If you look at the file, you’ll see 4 sections:

  1. Lines requiring ruby gems.
  2. A few defined helper functions.
  3. A list of temperatures and their HSL values.
  4. Running code that gets the temperature and sets the light.

You’ll likely find yourself bouncing around as you write the various sections.

Step 1: Get the temperature

The first thing the script needs is the temperature. There are two ways to get it: through an argument in the script (useful for testing), or a Weather API. This is a simple script that pulls the current temperature from the API forecast results.

```ruby if temp = ARGV[0] # Get the temperature from the first argument. temp = temp.to_i else # Get the temperature from the weather2 api url = “http://www.myweather2.com/developer/forecast.ashx?uac=#{ENV[“WEATHER2_TOKEN”]}&temp_unit=f&output=json&query=#{ENV[“WEATHER2_QUERY”]}” res = Faraday.get(url) if res.status != 200 puts res.status puts res.body exit end

data = JSON.parse(res.body) temp = data[“weather”][“curren_weather”][0][“temp”].to_i end ```

Step 2: Choose a color based on the temperature

I wanted the color to match color ranges on local news forecasts.

Our initial attempt required used color math to calculate the color between set values in 5 degree increments. This required us to specify 25 colors between -20 and 100 degrees. When we did that, we noticed a pattern:

  1. The saturation and brightness values didn’t change much.
  2. The hue value started high and eventually went down to zero.

My son saw this, and suggested that we simply calculate the hue for a temperature, leaving the saturation and brightness values the same. So then I talked him through a simple algorithm based on some math concepts he’d learned.

First, we set an upper and lower bound that we wanted to track. We decided to track from -20 to 100. The Hue light takes values from 0 to 65535.

ruby HUE = { -20 => 60_000, # a deep purple 100 => 0, # bright red }

The #hue_for_temp method gets the color range of any of the highest mapped temperature below the actual temperatur. It then uses a ratio to get the hue based on a range of hues.

For example:

```ruby temp = 50 full_range = 120 # 100 - -20 temp_range = 60 # 40 - -20 temp_perc = temp_range / full_range.to_f

full_hue_range = 60_000 # HUE[-20] - HUE[100] hue_range = full_hue_range * temp_perc hue = min_hue - hue_range ```

The #hue_for_temp method lets us set hue values for any temperature we want, too. While checking the output colors, my son wanted to set 50 to green for “hoodie weather.” This means that 60 is a really light yellow. 70 is orange, meaning we can leave off any light jackets. This is the set of mapped temperatures that we ended with:

ruby HUE = { -20 => 60_000, 50 => 25_500, 100 => 0, }

Step 3: Set the light color

Now that we have the HSL values for the temperature, it’s time to set the Philip Hue light. First, create a state object for the light:

ruby state = { :on => true, :hue => hue_for_temp(temp), :sat => 255, :bri => 200, # performs a smooth transition to the new color for 1 second :transitiontime => 10, }

A simple HTTP PUT call will change the color.

ruby hueapi = Faraday.new ENV["HUE_API"] hueapi.put "/api/#{ENV["HUE_USER"]}/lights/#{ENV["HUE_LIGHT"]}/state", state.to_json

Step 4: Schedule the script

If you don’t want to set the environment variables each time, you can create a .env file in the root of the application.

WEATHER2_TOKEN=MONKEY WEATHER2_QUERY=38.8417832,-105.0438213 HUE_API= HUE_USER=technoweenie HUE_LIGHT=1

You can then run the script with dotenv:

$ dotenv ruby weatherhue.rb 75

A crontab can be used to run this every 5 minutes. Run crontab -e to add a new entry:

# note: put tabs between the `*` values
*/5 * * * * cd /path/to/script; dotenv ruby weatherhue.rb

Confirm the crontab with crontab -l.

Bonus Round

  1. Update the script to use the forecast for the day, and not the current temperature.
  2. Set a schedule that automatically only keeps the light on in the mornings when you actually care what the temperature will be.

I hope you enjoyed this little tutorial. I’d love to hear any experiences from working with it! Send me pictures or emails either to the GitHub issue for this post, or my email address.