The Blog of Ian Mercer.

Showing home status with just a single RGB LED

Cover Image for 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.

Related Stories

Cover Image for Home Automation

Home Automation

I've been working on home automation for over 15 years and I'm close to achieving my goal which is a house that understands where everyone is at all times, can predict where you are going next and can control lighting, heating and other systems without you having to do or say anything. That's a true "smart home".

Ian Mercer
Ian Mercer
Cover Image for Digital Twins are never identical

Digital Twins are never identical

Digital Twin are an online representation of a real world object, a copy of its properties in the digital world and a way to send updated and commands to it. In effect I've been making them for years but now they have a trendy name.

Ian Mercer
Ian Mercer
Cover Image for Home Automation Sensors

Home Automation Sensors

An overview of the many sensors I've experimented with for home automation including my favorite under-floor strain gauge, through all the usual PIR, beam and contact sensors to some more esoteric devices like an 8x8 thermal camera.

Ian Mercer
Ian Mercer
Cover Image for Why smarthomes are hard

Why smarthomes are hard

Why automated learning is hard for a smart home. The perils of over-fitting, under-fitting and how the general unpredictable nature of life makes it hard to build a system that learns your behavior.

Ian Mercer
Ian Mercer
Cover Image for Collinearity test for sensor data compression

Collinearity test for sensor data compression

One way to reduce the volume of sensor data is to remove redundant points. In a system with timestamped data recorded on an irregular interval we can achieve this by removing co-linear points.

Ian Mercer
Ian Mercer
Cover Image for Event blocks

Event blocks

Home automation systems need to respond to events in the real world. Sometimes it's an analog value, sometimes it's binary, rarely is it clean and not susceptible to problems. Let's discuss some of the ways to convert these inputs into actions.

Ian Mercer
Ian Mercer
Cover Image for Logistic function - convert values to probabilities

Logistic function - convert values to probabilities

Another super useful function for handling sensor data and converting to probabilities is the logistic function 1/(1+e^-x). Using this you can easily map values onto a 0.0-1.0 probability range.

Ian Mercer
Ian Mercer
Cover Image for ATAN curve for probabilities

ATAN curve for probabilities

In a home automation system we often want to convert a measurement into a probability. The ATAN curve is one of my favorite curves for this as it's easy to map overything onto a 0.0-1.0 range.

Ian Mercer
Ian Mercer
Cover Image for Home Construction Advice

Home Construction Advice

Several years ago we did a major remodel. I did all of the finish electrical myself and supervised all of the rough-in electrical. I also put in all of the electrical system and water in our barn. I have opinions ...

Ian Mercer
Ian Mercer
Cover Image for T-Mobile home internet

T-Mobile home internet

I'm testing a T-Mobile Home Internet device as a backup to XFinity and a way to offload half our monthly traffic to avoid the XFinity 1.2TB cap

Ian Mercer
Ian Mercer
Cover Image for Probabilistic Home Automation

Probabilistic Home Automation

A probabilistic approach to home automation models the probability that each room is occupied and how many people are in that room.

Ian Mercer
Ian Mercer
Cover Image for Multiple hypothesis tracking

Multiple hypothesis tracking

A statistical approach to understanding which rooms are occupied in a smart house

Ian Mercer
Ian Mercer
Cover Image for A state machine for lighting control

A state machine for lighting control

An if-this-then-that style rules machine is insufficient for lighting control. This state machine accomplishes 90% of the correct behavior for a light that is controlled automatically and manually in a home automation system.

Ian Mercer
Ian Mercer
Cover Image for Home Automation States

Home Automation States

Understanding the many different 'states' a house can have is critical to creating great home automation

Ian Mercer
Ian Mercer
Cover Image for Graphing gigabytes of home automation data with tableau

Graphing gigabytes of home automation data with tableau

Some interesting charts from the gigabytes of data my home automation system produces

Ian Mercer
Ian Mercer
Cover Image for iBeacons for Home Automation

iBeacons for Home Automation

My investigations into using iBeacons for home automation

Ian Mercer
Ian Mercer
Cover Image for iBeacon meetup in Seattle - January 2015

iBeacon meetup in Seattle - January 2015

My notes on the iBeacon meetup in Seattle held in January 2015

Ian Mercer
Ian Mercer
Cover Image for Home Automation Systems as a Graph

Home Automation Systems as a Graph

Using nodes and links to represent a home and all the devices in it

Ian Mercer
Ian Mercer
Cover Image for N-Gram Analysis of Sensor Events in Home Automation

N-Gram Analysis of Sensor Events in Home Automation

Using n-gram analysis to spot patterns in sensor activations

Ian Mercer
Ian Mercer
Cover Image for Xamarin Forms Application For Home Automation

Xamarin Forms Application For Home Automation

Building a Xamarin Forms application to control my home automation system

Ian Mercer
Ian Mercer
Cover Image for The Internet of Hubs (and things)

The Internet of Hubs (and things)

Maybe it should be called the Internet of Hubs instead

Ian Mercer
Ian Mercer
Cover Image for A wireless sensor network using Moteino boards

A wireless sensor network using Moteino boards

The diminutive Arduino boards include a powerful transmitter/receiver

Ian Mercer
Ian Mercer

JSON Patch - a C# implementation

Ian Mercer
Ian Mercer
Cover Image for The home as a user interface

The home as a user interface

Ian Mercer
Ian Mercer

A RESTful API for sensor data

POSTing data to a home automation system from Arduino devices

Ian Mercer
Ian Mercer
Cover Image for The Internet of Boilers

The Internet of Boilers

An experiment to measure every aspect of an HVAC / boiler system

Ian Mercer
Ian Mercer

VariableWithHistory - making persistence invisible, making history visible

A novel approach to adding history to variables in a programming language

Ian Mercer
Ian Mercer
Cover Image for A Quantified House - My Talk to the Seattle Quantified Self Meetup

A Quantified House - My Talk to the Seattle Quantified Self Meetup

My talk to the Seattle Quantified Self meetup

Ian Mercer
Ian Mercer

Integrating an Android phone into my home automation system

Some new features for my home automation using an Android phone

Ian Mercer
Ian Mercer

Before there was the web there was BeebTel

Just thought I should mention that I built a web-like system before the web existed

Ian Mercer
Ian Mercer

My first programme [sic]

At the risk of looking seriously old, here's something found on a paper tape

Ian Mercer
Ian Mercer
Cover Image for The Internet of Dogs

The Internet of Dogs

Connecting our dog into the home automation

Ian Mercer
Ian Mercer
Cover Image for GreenGoose Review

GreenGoose Review

A review of the now defunct GreenGoose sensor system

Ian Mercer
Ian Mercer
Cover Image for Home power meters revisited

Home power meters revisited

Ian Mercer
Ian Mercer
Cover Image for Home Automation Calendar Integration

Home Automation Calendar Integration

Ian Mercer
Ian Mercer

Web site crawler and link checker (free)

Ian Mercer
Ian Mercer

Smart home energy savings - update for 2010

Ian Mercer
Ian Mercer
Cover Image for A smart power strip

A smart power strip

Ian Mercer
Ian Mercer
Cover Image for What does a Smart House do at Halloween?

What does a Smart House do at Halloween?

My favorite home automation features for Halloween

Ian Mercer
Ian Mercer
Cover Image for Home Automation Top Features

Home Automation Top Features

Ian Mercer
Ian Mercer
Cover Image for Weather Forecasting for Home Automation

Weather Forecasting for Home Automation

Ian Mercer
Ian Mercer
Cover Image for How can I tell if my house is smart?

How can I tell if my house is smart?

Ian Mercer
Ian Mercer

Home Automation Block Diagram

Ian Mercer
Ian Mercer

Elliott 803 - An Early Computer

Ian Mercer
Ian Mercer

World's Smartest House Demonstration

Ian Mercer
Ian Mercer

Looking forward to the new year and our new datacenter

Historical note about moving my servers into a datacenter

Ian Mercer
Ian Mercer

Future proof your home with a new conduit system?

Running conduit can be expensive but maybe you don't need one to every room

Ian Mercer
Ian Mercer

Second Drobo Update

At this point things were looking up for my Drobo

Ian Mercer
Ian Mercer

It's all about disk speed

Why disk speed is the most critical aspect for most modern PCs and servers

Ian Mercer
Ian Mercer

Comcast woes and a new monitoring utility

Monitoring a cable modem using its HTML management interface

Ian Mercer
Ian Mercer

Core duo desktop machine runs cool

Ian Mercer
Ian Mercer
Cover Image for New Home Automation Server

New Home Automation Server

Ian Mercer
Ian Mercer
Cover Image for World's Smartest House

World's Smartest House

Over 15 years of experimentation with home automation

Ian Mercer
Ian Mercer
Cover Image for World's Smartest House Videos

World's Smartest House Videos

A collection of videos about my smart home efforts

Ian Mercer
Ian Mercer