Showing home status with just a single RGB LED

This week I decided to try out the Bluno (Bluetooth + Arduino Uno) and WiDo (WiFi + Arduino Lenardo) modules that I’d ordered from DFRobot.

The Bluno investigation was fairly short-lived: it works as advertised but it cannot scan for Bluetooth devices which is how I was hoping to use it.

Moving on to the WiDo, this is a very cheap way to get an Arduino + WIFI. It worked well despite the rather small on-board WIFI antenna. I added a NeoPixel single RGB LED to it on digital output 6.

After a short while configuring it to scan for SSIDs and connect to my local network I was able to get it calling out to my home automation server using POST requests. I quickly added a new API to report how recently each major area of the house had been occupied (minutes since last triggered) that produces JSON like this:

{
"first": 1.5860427216666666,
"second": 29.900604178333335,
"basement": 196.46606494,
"barn": 446.73795961333332,
"driveway": 162.16262138333335,
"kitchen": 86.293791955
}

I quickly found many of the ways the WiDo could hang during Http requests and SSID scanning / joining networks so I plugged one of my Arduino Watchdog boards on top after moving the jumper from the ~10s position to ~40s.

I used the Adafruit library to connect to the server and make the request. Avoiding memory allocations is usually the best approach on a small memory device like this so I have a fixed buffer into which I read the response rather than using `String` or any other class that makes dynamic allocations.

  int count = 0;
  
  /* Read data until either the connection is closed, or the idle timeout is reached. */ 
  unsigned long lastRead = millis();
  while (www.connected() && (millis() - lastRead < IDLE_TIMEOUT_MS)) {
    while (www.available()) {
      char c = www.read();
      if (count < responseBufferLength)
        responseBuffer[count++] = c;
      lastRead = millis();
    }
  }

Parsing JSON in Arduino isn’t trivial. There is a library that many people recommend but it takes up a fair amount of RAM and I wanted something simpler so I used my trusty ‘cheat’ parsing code that looks for a string, skips a few characters and then reads a number:

static double getJsonDouble(const char* buffer, const char* name) {
  char* p = strstr(buffer, name) + strlen(name) + 2;
  if (p != NULL) {
    return atof(p);
  }
  return -1;
}

static int getJsonInt(const char* buffer, const char* name) {
  char* p = strstr(buffer, name) + strlen(name) + 2;
  if (p != NULL) {
    return atoi(p);
  }
  return -1;
}

Using this it’s easy to get each of the values being passed back from the API call:

     double firstFloor = getJsonDouble((char*)responseBuffer, "\"first\"");

I decided to color the LED with Blue for barn, Green for house and Red for driveway with the brightness fading out the longer it has been since the last trigger. I also blip the LED to off each time any of the values reduces because that indicates it was triggered since last time it was read.

So now, at a glance I can see what’s happening at home: Red = a car came down the drive but nobody is home, Yellow = a car came down the drive and someone is home, Green = someone is home, Blue = Someone is in the barn, White = lots happening, Black = all quiet, nobody around! Based on the brightness I can tell how recently each area was occupied.

Overall this one solitary RGB LED conveys quite a lot of information about what’s happening at home. With a quick reconfigure of the SSID and password I had it running on my desk at work. Now I just need to put it in a translucent orb casing to make it look more attractive.

I’m also planning on building a few more to indicate other interesting data about the house, maybe one connected to my traffic alerts, another to my delta-weather reports, … But rather than putting these out on desks as visible orbs I’m planning on putting them in places where they can cast a subtle light onto a wall – i.e. not something a visitor would notice but something we can see as we walk around – a ‘glanceable information source.

The post Showing home status with just a single RGB LED appeared first on Ian Mercer.