Hackbright Workshop

Building Connected Things
with Electric Imp
These slides are licensed under the MIT License
http://opensource.org/licenses/MIT
SSID: impdemo
PW: electric
Matt Haines | Tom Byrne
matt@electricimp.com | tom@electricimp.com
@beardedinventor | @tlbyrn

Agenda
The Internet of Things
• What is the Internet of Things
• What does the Internet of Things space look like
• What goes into an Internet of Things application
• Overview of the Electric Imp platform
Workshop – Your first imp project
• Getting your first imp online
• Digital I/O
• Building a basic HTTPS request handler
• Making HTTP requests

The Internet of Things (2025)
50B
Connected
Devices
$6.2T
Economic
Impact
McKinsey Global Institute, 2013

What Goes Into an IoT Application
• Hardware
• Microcontrollers, radios, sensors, actuators, etc
• Firmware
• Device logic, drivers, network stack, etc
• Server Code
• Heavy processing, external device API, data storage, etc
• External Web Services
• Weather APIs, Twitter, Twilio, Gmail/email, IFTTT, etc
• App / Website / Etc
• User interface, OAuth, etc
• Areas of knowledge required:
• Electrical Engineering, embedded software, security, backend/server
development, web development, database admin, app development, …

The Electric Imp Platform
Connectivity Infrastructure
In-house
Great products
Focus on the
core business
Platform
Server Infrastructure
In-house
Great products
Focus on the
core business
Platform

The Electric Imp Platform – Overview

The Electric Imp Platform - Devices
• 32-Bit ARM Cortex M3 processor
• 802.11 b/g/n WiFi
• Open WiFi, WEP, WPA, WPA2
• 80 KB* code space (device – 'firmware')
• 6/12 Configurable GPIO Pins
• Digital In/Out
• Analog In
• 12 bit DAC (Analog Out)
• PWM Out
• I2C, UART, SPI
* This value changes a little bit each release (the imp originally only had about 40 KB of code space)

The Electric Imp Platform - Agents
• Micro-server than can act on behalf of a device
• Runs on the Electric Imp Servers
• 1 MB code space
• 1MB RAM
• Allows you to do things that you typically can’t on an embedded processor
• Process incoming HTTP requests (create APIs for your device)
• Make outgoing HTTP requests (interact with external APIs)
• Persist small amounts of data

BlinkUp - Getting Online
• Create an Electric Imp Account: https://ide.electricimp.com
• Download the Electric Imp mobile app:
• Android: play.google.com/store/apps/details?id=com.electricimp.electricimp
• iPhone: itunes.apple.com/us/app/electric-imp
• Sign into the app with your Electric Imp Account
• Enter WiFi credentials:
• SSID: impdemo
• PW: electric
• Power up your imp
• The imp’s internal LED must be blinking before continuing to the next step
• Click BlinkUp in the mobile app
• Hold screen of phone against blinking light of imp until BlinkUp is complete
• Your device should now be blinking green (online)*
* Your imp will stop blinking after 1 minute to save power (it is still powered on)

BlinkUp Example
* Your imp will stop blinking after 1 minute to save power (it is still powered on)

Digital Output - Device Code
// Device Code
led <- hardware.pin9;
led.configure(DIGITAL_OUT);
state <- 0;
function blink() {
imp.wakeup(1.0, blink);
state = 1 – state;
led.write(state);
}
blink();

Blocking Loops are Bad!
// Device Code
// NOTE: THIS IS BAD CODE:
function loop() {
local state = 0;
while (1) {
led.write(state);
state = 1 – state;
imp.sleep(1.0);
}
}
loop();

Digital Input - Device Code
// Device Code:
button <- hardware.pin1;
function onButton() {
local state = button.read();
led.write(state);
}
button.configure(DIGITAL_IN_PULLUP, onButton);

Event Driven Programming and Callbacks
• Squirrel is an Event Driven Language
• Behaviour is defined by events and callbacks
• An event is a pre-programmed thing that can happen:
• The timeout on an imp.wakeup ends
• The state of a DIGITAL_IN pin changes
• A message is passed from the device to the agent or vice versa
• An agent receives an incoming HTTP request
• A callback is a function bound to a event:
• imp.wakeup(5, blink);
• Tells the imp to run the function called blink in 5 seconds
• button.configure(DIGITAL_IN, onButton);
• Tells the imp to run the function called onButton when the state of the pin
assigned to button changes

HTTP Handlers
• Each device has an agent – a tiny micro servers that act on behalf of their device
• Each agent has a unique URL associated with it (see below)
• http.onrequest binds a callback to the 'received incoming HTTP Request' event

HTTP Handler – Agent Code
// Agent Code:
function httpHandler(request, response) {
if ("state" in request.query) {
local state = request.query["state"];
device.send("led", state);
}
response.send(200, "OK");
}
http.onrequest(httpHandler);

HTTP Handler – Device Code
// Device Code:
function ledHandler(data) {
if (data == "0") {
server.log("LED OFF")
led.write(0);
} else {
server.log("LED ON");
led.write(1);
}
}
agent.on("led", ledHandler);

Making HTTP Requests – Device Code
// Device Code:
function ledHandler(data) {
if (data == "0") {
server.log("LED OFF")
led.write(0);
} else {
server.log("LED ON");
led.write(1);
}
}
agent.on("led", ledHandler);

Making HTTP Requests – Agent Code
// Add to the bottom of your agent code:
const URL = "https://agent.electricimp.com/RO5HOrveo4I1";
function buttonPressHandler(state) {
local url = URL + "?state=" + state;
local request = http.get(url);
request.sendasync(function(resp) {
server.log(resp.statuscode + " - " + resp.body);
});
}
device.on("buttonPress", buttonPressHandler)

Other activities
• Device:
• Try to control your LED with PWM
• electricimp.com/docs/examples/pwm-led
• Bonus: Try to control the brightness with a web request
• Create multiple “states” for your LED (on, off, blinking slow, blinking fast)
• Make the button switch between states
• Agent:
• Grab the Wunderground API code
• github.com/electricimp/reference/tree/master/webservices/wunderground
• Grab weather every 5 mins and change the brightness of the LED based on
the temperature
• Bonus: Create an Umbrella reminder to keep by your front door:
• Every morning the agent checks the weather
• If there’s > 50% chance of rain, LED turns on
• Grab the Twitter API
• github.com/electricimp/reference/tree/master/webservices/twitter
• Make your imp tweet whenever the button is pressed
• Bonus: Control the state of the LED based on a Twitter stream
• Turn the light on whenever something is tweeted with a tracked tag
• Click the button to clear the light

Electric Imp Resource
Getting Started Guide electricimp.com/docs/getting-started
API Documentation electricimp.com/docs/api
Squirrel Documentation electricimp.com/docs/squirrel
Reference Code github.com/electricimp/reference
Community Blog community.electricimp.com
Forums forums.electricimp.com

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