Tutorial 3: Feed it real data¶

This tutorial replaces the random numbers from tutorial 2 with a real weather forecast.

The app from tutorial 2 already keeps state, refreshes on a timer, survives a reboot and has settings. The main change is where the numbers come from. Because the work already happens in loop(), draw() stays almost the same.

We use Open-Meteo, which needs no account and no API key.

The tutorial goes in five steps. The first one gives you a working app. The others make it more robust and lighter on memory.

Look at the answer first¶

Before writing any code against a web service, look at what it answers. Open this address in a browser, with your own latitude and longitude in place of Berlin's:

https://api.open-meteo.com/v1/forecast?latitude=52.52&longitude=13.40&hourly=precipitation_probability&forecast_hours=16&timezone=auto

forecast_hours=16 asks for exactly sixteen values, which is what the display has room for. timezone=auto makes the first of them the hour you are in right now.

The answer looks like this:

{"latitude":52.52,"longitude":13.4,"generationtime_ms":0.04,"utc_offset_seconds":7200,
"timezone":"Europe/Berlin","timezone_abbreviation":"GMT+2","elevation":30.0,
"hourly_units":{"time":"iso8601","precipitation_probability":"%"},
"hourly":{"time":["2026-08-09T19:00","2026-08-09T20:00", … fourteen more … ],
"precipitation_probability":[0,0,0,0,0,0,0,5,28,18,5,0,3,0,0,0]}}

The sixteen numbers we want are in "hourly", under "precipitation_probability".

Step 1: Fetch the forecast¶

A web request takes time: usually a fraction of a second, sometimes much longer. AWTRIX never lets an app wait for it, because a waiting app would freeze the display for every app.

So http.get() works with a callback: a function you hand over, which AWTRIX calls later.

      http.get(self.url, / b, st -> self.on_body(b, st))

• http.get() sends the request and returns at once. Your loop() carries on.
• When the answer is there, AWTRIX calls your function, once, between two frames.
• / b, st -> self.on_body(b, st) is a short way to write a small function. It takes the two values AWTRIX passes in, the answer b and the status st, and hands them on to your own method on_body().

on_body(body, status) then gets two values:

• body is the answer as text. It is nil (no value) when nothing came back at all: no Wi-Fi, a wrong address, or no answer within thirty seconds. status is then 0.
• status is the HTTP status code. 200 means everything is fine. A server that answers with an error, for example 404 or 500, still sends a body, but not the one you want.

So the handler starts with one check: if body == nil || status != 200 return end.

json.load(body) turns the answer text into Berry maps and lists. After that, data["hourly"]["precipitation_probability"] is the list of sixteen numbers.

Here is the complete app. Paste it over your Rain script and save:

# @name    Rain
# @desc    Chance of rain for the next 16 hours, from Open-Meteo
# @version 1.0
# @config  lat   text   "Latitude"  default="52.52" help="Decimal degrees, north positive"
# @config  lon   text   "Longitude" default="13.40" help="Decimal degrees, east positive"
# @config  every number "Refresh"   default=15 min=1 max=60 unit=min
# @config  tint  color  "Bar color" default=#0088FF

import json

class Rain
  var hours       # 16 percentages, this hour first
  var url         # the address to fetch, built from the settings
  var tint        # bar color
  var period      # loop() calls between fetches
  var ticks       # counting down to the next fetch

  def init()
    self.url = "https://api.open-meteo.com/v1/forecast" +
               "?hourly=precipitation_probability&forecast_hours=16&timezone=auto" +
               "&latitude=" + store.get("lat") +
               "&longitude=" + store.get("lon")
    self.tint = store.get("tint")
    self.period = store.get("every") * 60
    self.ticks = 0
    self.hours = store.get("hours")
    if self.hours == nil
      self.hours = []
      for i : 0 .. 15
        self.hours.push(0)
      end
    end
  end

  def loop()
    if self.ticks <= 0
      self.ticks = self.period
      http.get(self.url, / b, st -> self.on_body(b, st))
    end
    self.ticks -= 1
  end

  def on_body(body, status)
    if body == nil || status != 200 return end
    var data = json.load(body)
    if data == nil return end
    var list = data["hourly"]["precipitation_probability"]
    if size(list) < 16 return end
    for i : 0 .. 15
      self.hours[i] = num(list[i], 0)
    end
    store.set("hours", self.hours)
  end

  def draw()
    clear()
    var h = height()
    var w = width() / size(self.hours)
    for i : 0 .. size(self.hours) - 1
      var v = self.hours[i]
      var bar = v * h / 100
      if bar > 0
        rect_fill(i * w, h - bar, w, bar, self.tint)
      end
    end
  end
end

return Rain()

Open Apps, press ⚙ on the app's row, and put your own latitude and longitude in. Decimal degrees, so Berlin is 52.52 and 13.40. Saving the settings restarts the app, and the first fetch goes out straight away.

A few details:

• json is not built in like http, so the script starts with import json.
• json.load() returns nil when the text is not valid JSON. The app then keeps its old values.
• num(list[i], 0) returns the value as a number, or 0 if the service sent no value for that hour.
• self.hours[i] = … changes the existing list in place. draw() paints the new values on the next frame.

Step 2: Don't fetch twice at once¶

If the network is slow and your timer fires again, several requests can be waiting at once, and each one uses memory. The fix is one member that says "a request is on its way":

  def loop()
    if self.ticks <= 0
      self.ticks = self.period
      if !self.in_flight
        self.in_flight = true
        http.get(self.url, / b, st -> self.on_body(b, st))
      end
    end
    self.ticks -= 1
  end

  def on_body(body, status)
    self.in_flight = false
    if body == nil || status != 200 return end
    # the rest of the handler as before
  end

Add var in_flight to the class and self.in_flight = false to init().

Clear the flag on the first line of the handler, before any check that might return early. If the handler returns before clearing it, the app thinks a request is still running and never fetches again.

Choose a long interval. A bare http.get() in loop() fires once a second, which helps nobody and puts load on the service. Weather every five to fifteen minutes is enough. The interval is a @config setting, so the user can make it slower without editing code.

Step 3: Before the first answer¶

Between installing the app and the first successful answer there are a few seconds, or after a restart a few tens of seconds, where you have nothing to show. Never leave the display blank.

Add a member ready that says "we have real numbers". It is true when the store already holds values from an earlier run. on_body() sets self.ready = true once it has stored the new values, and draw() shows a dim placeholder until then. The changed parts, in their place in the class:

class Rain
  var hours, ready   # and the other members, as before

  def init()
    self.hours = store.get("hours")
    self.ready = self.hours != nil
    if !self.ready
      self.hours = []
      for i : 0 .. 15
        self.hours.push(0)
      end
    end
    # the rest of init(), as before
  end

  def draw()
    clear()
    if !self.ready
      text(1, 6, "...", 0x444444)
      return
    end
    # the bars, as before
  end
end

return Rain()

Until the first answer arrives, a new install shows three dim dots.

The other option is to skip the turn entirely. AWTRIX asks should_show() when the rotation arrives at your app. Returning false sends it straight on to the next one:

  def should_show()
    return self.ready
  end

Which one to use:

• A dim placeholder means "this app is waiting for data". Use it when data is expected soon.
• should_show() returning false means "nothing to report". Use it for an app that is often empty, like a reminder that only shows on bin day.

A skipped app gets a dim marker on its row in the web UI, so you can see why it did not appear.

This app uses the placeholder. After the first successful run it has stored values, so the gap only ever appears once.

Step 4: Make it lighter¶

The app works. Now look at what it costs.

All scripts on the device share one block of memory. By default the whole answer lands there as one piece of text, up to 8 KB. json.load() then builds maps, lists and strings from it, several times the size of the text. Our answer is small, because we asked for only sixteen hours. Many services answer with several kilobytes, and on a device with little memory that is enough to make other apps fail.

We only want the sixteen numbers at the very end of the answer. So we ask AWTRIX to keep only that part.

Keep only a window of the answer¶

The find and keep options make AWTRIX search the answer while it arrives. It keeps only a small window. The window starts where your search text (the needle) first appears:

      http.get(self.url, / b, st -> self.on_body(b, st),
               {'find': "\"precipitation_probability\":[", 'keep': 128})

body is then the 128 characters starting at the match, needle included. The size of the whole answer does not matter. A value far into a long answer costs the same as one at the start.

Look closely at the needle. It ends with [, and that bracket is important: the text "precipitation_probability" also appears earlier, inside hourly_units, where its value is "%". Without the bracket we would match the units and get the wrong window.

Inside a Berry string, \" stands for a quote character. So the needle is the text "precipitation_probability":[ with its quotes.

If the needle never appears, the callback gets nil as body, with the real status code. An error answer from the server does not contain the needle either, so the one check if body == nil return end covers every failure.

Getting sixteen numbers out of the window¶

The window is now this, and it is not valid JSON on its own:

"precipitation_probability":[0,0,0,0,0,0,0,5,28,18,5,0,3,0,0,0]}}

So json.load() cannot read it. We do not need it: a regular expression, a small search pattern, gets the sixteen numbers without building anything else:

    var m = re.matchall("\\d+", body)

re.matchall() returns every match as a list. \d+ means "one or more digits". It is written "\\d+" because a backslash starts an escape in Berry strings too. The needle has no digits, so what comes back is exactly our sixteen numbers, as text. int(m[i]) turns the text "28" into the number 28.

re is built in and needs no import.

This is the recommended form for every app that fetches regularly: find and keep to get a small window, and re to take the values out of it.

Step 5: The finished app¶

Everything from steps 1 to 4 together, plus two small extras explained below: a dim line along the bottom, and the middle button to fetch at once.

# @name    Rain
# @desc    Chance of rain for the next 16 hours, from Open-Meteo
# @author  awtrix-ng
# @version 1.0
# @config  lat   text   "Latitude"  default="52.52" help="Decimal degrees, north positive"
# @config  lon   text   "Longitude" default="13.40" help="Decimal degrees, east positive"
# @config  every number "Refresh"   default=15 min=1 max=60 unit=min
# @config  tint  color  "Bar color" default=#0088FF

class Rain
  var hours          # 16 percentages, this hour first
  var url, tint      # built from the settings in init()
  var period, ticks  # loop() calls between fetches, and the countdown
  var in_flight      # a request is on its way
  var ready          # we have real numbers to show

  def init()
    self.url = "https://api.open-meteo.com/v1/forecast" +
               "?hourly=precipitation_probability&forecast_hours=16&timezone=auto" +
               "&latitude=" + store.get("lat") +
               "&longitude=" + store.get("lon")
    self.tint = store.get("tint")
    self.period = store.get("every") * 60
    self.ticks = 0
    self.in_flight = false

    self.hours = store.get("hours")
    self.ready = self.hours != nil
    if !self.ready
      self.hours = []
      for i : 0 .. 15
        self.hours.push(0)
      end
    end
  end

  def on_body(body, status)
    self.in_flight = false
    if body == nil return end
    var m = re.matchall("\\d+", body)
    if size(m) < 16 return end
    for i : 0 .. 15
      self.hours[i] = int(m[i])
    end
    self.ready = true
    store.set("hours", self.hours)
  end

  def loop()
    if self.ticks <= 0
      self.ticks = self.period
      if !self.in_flight
        self.in_flight = true
        http.get(self.url, / b, st -> self.on_body(b, st),
                 {'find': "\"precipitation_probability\":[", 'keep': 128})
      end
    end
    self.ticks -= 1
  end

  def draw()
    clear()
    if !self.ready
      text(1, 6, "...", 0x444444)
      return
    end
    var h = height()
    var w = width() / size(self.hours)
    line(0, h - 1, width() - 1, h - 1, 0x101820)
    for i : 0 .. size(self.hours) - 1
      var v = self.hours[i]
      var bar = v * h / 100
      if bar > 0
        rect_fill(i * w, h - bar, w, bar, self.tint)
      end
    end
  end

  def on_button(btn)
    if btn == "select"
      self.ticks = 0
      return true
    end
  end
end

return Rain()

The app does not use json, so it has no import json line.

Set Refresh to 1 minute while you are testing, and put it back afterwards.

The middle button¶

on_button(btn) runs when a button is pressed while your app is shown. btn is "left", "select" or "right". Here the middle button ("select") sets the countdown to zero, so the next loop() fetches at once. That saves a lot of waiting while you test. Returning true tells AWTRIX that the app handled the press, so the button does nothing else.

The dim line along the bottom¶

One line in draw() has nothing to do with fetching. It makes a quiet display look intentional:

    line(0, h - 1, width() - 1, h - 1, 0x101820)

On a dry day all sixteen percentages are zero or close to it. Almost no bar is drawn, and the display is nearly dark. The app works, but it looks broken.

The dim line fixes that with one call. "No rain" shows as a flat line, and a completely blank display means something is wrong. Any app that draws values that can drop to zero benefits from this.

Compare this with tutorial 2. draw() got a placeholder and a line. loop() calls http.get() instead of math.rand(). Everything else is new methods next to the old ones.

Let the firmware draw the chart¶

The hand-drawn bars show how coordinates work. AWTRIX can also draw the chart for you with bar_chart(). This is the same app with the built-in chart:

# @name    Rain
# @desc    Chance of rain for the next 16 hours, from Open-Meteo
# @author  awtrix-ng
# @version 1.0
# @config  lat   text   "Latitude"  default="52.52" help="Decimal degrees, north positive"
# @config  lon   text   "Longitude" default="13.40" help="Decimal degrees, east positive"
# @config  every number "Refresh"   default=15 min=1 max=60 unit=min
# @config  tint  color  "Bar color" default=#0088FF

class Rain
  var hours          # 16 percentages, this hour first
  var bars           # the same values as bar heights, 0 to 8
  var url, tint      # built from the settings in init()
  var period, ticks  # loop() calls between fetches, and the countdown
  var in_flight      # a request is on its way
  var ready          # we have real numbers to show

  def init()
    self.url = "https://api.open-meteo.com/v1/forecast" +
               "?hourly=precipitation_probability&forecast_hours=16&timezone=auto" +
               "&latitude=" + store.get("lat") +
               "&longitude=" + store.get("lon")
    self.tint = store.get("tint")
    self.period = store.get("every") * 60
    self.ticks = 0
    self.in_flight = false

    self.hours = store.get("hours")
    self.ready = self.hours != nil
    if !self.ready
      self.hours = []
      for i : 0 .. 15
        self.hours.push(0)
      end
    end
    self.bars = []
    self.scale()
  end

  def scale()
    self.bars.clear()
    for v : self.hours
      self.bars.push(v * 8 / 100)
    end
  end

  def on_body(body, status)
    self.in_flight = false
    if body == nil return end
    var m = re.matchall("\\d+", body)
    if size(m) < 16 return end
    for i : 0 .. 15
      self.hours[i] = int(m[i])
    end
    self.scale()
    self.ready = true
    store.set("hours", self.hours)
  end

  def loop()
    if self.ticks <= 0
      self.ticks = self.period
      if !self.in_flight
        self.in_flight = true
        http.get(self.url, / b, st -> self.on_body(b, st),
                 {'find': "\"precipitation_probability\":[", 'keep': 128})
      end
    end
    self.ticks -= 1
  end

  def draw()
    clear()
    if !self.ready
      text(1, 6, "...", 0x444444)
      return
    end
    line(0, height() - 1, width() - 1, height() - 1, 0x101820)
    bar_chart(self.bars, self.tint, false)
  end

  def on_button(btn)
    if btn == "select"
      self.ticks = 0
      return true
    end
  end
end

return Rain()

bar_chart(list, color, autoscale) spans the full display width and takes at most sixteen values. It leaves a one-pixel gap between the bars, so on a 32 pixel display each bar is one pixel wide.

The third argument, false, switches autoscaling off:

• With autoscaling on, the highest value always fills the display. A dry day with 5 % would look alarming.
• With autoscaling off, the scale is fixed from 0 to 8, and 8 fills the full height. So the chart needs bar heights from 0 to 8, not percentages. scale() converts the percentages into the list bars, once after each answer, so draw() only paints.

The color can also be a palette name. bar_chart(self.bars, "Ocean", false) colors each bar by its own height.

There is also line_chart() with the same arguments, and progress(pct) for a single value along the bottom row.

Which one to use: the built-in chart is one line and spaces the bars for you. The hand-drawn version lets you decide what a zero looks like, how wide a bar is, and where the color comes from. Start with bar_chart(), and write the loop when you need something it cannot do.

What you learned¶

• http.get() never waits. It returns at once, and AWTRIX calls your callback later, between two frames.
• body == nil means nothing useful arrived. Check it first in every handler.
• An in_flight member, cleared on the first line of the handler, stops requests piling up.
• Draw a placeholder or return false from should_show(), but never show an empty display.
• find and keep keep only a small window of the answer, and re.matchall() takes the values out of it. This saves more memory than anything else in an app that fetches.
• bar_chart() draws the chart for you.

Next¶

You have written a complete app. The four recipes are independent, and each one builds something different:

• Countdown, which needs no network at all
• MQTT status, for a device that already has a broker
• Sensor chart, using the clock's own thermometer
• Background doorbell, an app that never draws anything

If your device refuses to install scripts, or other apps start failing after you installed yours, read Keeping scripts small.

Related¶

• Scripting guide for the full HTTP, regular expression and charting reference
• Limits for response sizes, timeouts and how many requests may be in flight