Building the Internet of Things with Raspberry Pi

Who am I?

I am a Software Developer and Architect at Energy Partners

Caution – I am not an Electronic Engineer!

Building the Internet of Thingswith Raspberry Pi

Building the Internet of Thingswith Raspberry Pi

Building the Internet of Thingswith Raspberry Pi

Building the Internet of Thingswith Raspberry Pi

Model A Model B Model B+

$25 $35 $35

1 USB port 2 USB ports 4 USB ports

No Ethernet 10/100 Ethernet 10/100 Ethernet

SD card slot SD card slot Micro SD card slot

General-purpose input/output pins (GPIO)

Building the Internet of Thingswith Raspberry Pi

• GPIO pins can be configured to be input or output

• Input values are readable - HIGH or LOW (3v3 or 0v)

• Output values are writable/readable

The Hardware

Building the Internet of Thingswith Raspberry Pi

Building an Input Circuit

Opto-coupler / Opto-isolator

Transfers electrical signals between two isolated circuits by using light

Building the Internet of Thingswith Raspberry Pi

Building an Input Circuit

Building the Internet of Thingswith Raspberry Pi

Resistor

Implements electrical resistanceReduce current flow

Pull-up / pull-down resistors

• Pull-up resistors are connected to the high voltage (3.3V)

• Pull-down resistors are connected to ground

• Initialize an input pin to a known state when nothing is connected to it

Building the Internet of Thingswith Raspberry Pi

Pull-up resistor

Building an Input Circuit - The diagram

Building the Internet of Thingswith Raspberry Pi

Building an Output Circuit - The components

Building the Internet of Thingswith Raspberry Pi

Transistor

• Used to amplify and switch electronic signals and electrical power

• A voltage or current applied to one pair of the transistor's terminals changes the current through another pair of terminals.

Building an Output Circuit - The components

Relay

• Electrically operated switch• Many relays use an electromagnet to

mechanically operate a switch• To control a circuit by a low-power

signal

Building the Internet of Thingswith Raspberry Pi

Building an Output Circuit

Building the Internet of Thingswith Raspberry Pi

Veroboard / Stripboard

Building the Internet of Thingswith Raspberry Pi

26pin IDC ribbon cable + crimp connector

Building the Internet of Thingswith Raspberry Pi

Shortcuts!

Building the Internet of Thingswith Raspberry Pi

Accessories

The Software

Building the Internet of Thingswith Raspberry Pi

Building the Internet of Thingswith Raspberry Pi

Finding your Pi's hardware revision

cat /proc/cpuinfo

Code(s) Model and revision2 Model B Revision 1.03 Model B Revision 1.0 + ECN0001 4, 5, 6 Model B Revision 2.0

Building the Internet of Thingswith Raspberry Pi

Software considerations

• The software is the easy part!

• Possible to damage the Pi• Triple check your pin

configuration

Building the Internet of Thingswith Raspberry Pi

Introducing RPi.GPIO

• Depending on your distro, probably already installed

• If not, use pip: sudo pip install rpi.gpio

Building the Internet of Thingswith Raspberry Pi

Basic usage

#To import the RPi.GPIO module: import RPi.GPIO as GPIO

#Select the pin numbering scheme: GPIO.setmode(GPIO.BOARD) # or GPIO.setmode(GPIO.BCM)

Building the Internet of Thingswith Raspberry Pi

Exit Cleanly

• Inputs are safer than outputs• Shorting outputs to ground can damage the PI• Any ports not reset before script exit will

remain as is• Always perform cleanup before script exits

Building the Internet of Thingswith Raspberry Pi

Exit Cleanly

import RPi.GPIO as GPIO

# the rest of your code goes here

GPIO.cleanup() # remember, a program doesn't necessarily # exit at the last line!

Building the Internet of Thingswith Raspberry Pi

Inputs - Setupimport RPi.GPIO as GPIO

#GPIO numbering GPIO.setmode(GPIO.BCM)

channel = 7 GPIO.setup(channel, GPIO.IN, pull_up_down=GPIO.PUD_UP) # or GPIO.setup(channel, GPIO.IN, pull_up_down=GPIO.PUD_DOWN)

Building the Internet of Thingswith Raspberry Pi

Inputs - Pollingif GPIO.input(channel): print('Input was HIGH') else: print('Input was LOW')

# Or, in a loop while GPIO.input(channel) == GPIO.LOW: # wait 10 ms time.sleep(0.01)

Building the Internet of Thingswith Raspberry Pi

Inputs - wait_for_edge()

• blocks execution until an edge is detected• GPIO.RISING, GPIO.FALLING or GPIO.BOTH

GPIO.wait_for_edge(channel, GPIO.RISING)

Building the Internet of Thingswith Raspberry Pi

Inputs - event_detected()

• Designed to be used in a loop with other things

# add rising edge detection on a channel GPIO.add_event_detect(channel, GPIO.RISING) do_something() if GPIO.event_detected(channel): print('Button pressed')

Building the Internet of Thingswith Raspberry Pi

Inputs - Threaded callbacks

• RPi.GPIO runs a second thread for callback functions

GPIO.add_event_detect(channel, GPIO.RISING, callback=my_callback)

Building the Internet of Thingswith Raspberry Pi

Outputs - Setup

import RPi.GPIO as GPIO

GPIO.setmode(GPIO.BOARD)

GPIO.setup(12, GPIO.OUT)

Building the Internet of Thingswith Raspberry Pi

Outputs

#Set output to HIGH GPIO.output(12, GPIO.HIGH)

#Set output to LOW GPIO.output(12, GPIO.LOW)

#Read the state of the output GPIO.input(12)

Building the Internet of Thingswith Raspberry Pi

Example - Bell

Building the Internet of Thingswith Raspberry Pi

The Raspberry Pi Alarm

Building the Internet of Thingswith Raspberry Pi

On Github

Building the Internet of Thingswith Raspberry Pi

github.com/nbroers/hal

What’s next?

Building the Internet of Thingswith Raspberry Pi

Questions?

Building the Internet of Thingswith Raspberry Pi

Parts list12V input circuit:

• Optocoupler: LTV-847 - http://www.mantech.co.za/ProductInfo.aspx?Item=340M0324• Resistor: 1K Ohm - http://www.mantech.co.za/ProductInfo.aspx?Item=64M0009

Output circuit:

• Resistor: 100k ohm• Resistor: 10k ohm• Transistor (NPN Transistor): P2N2222AG - http://www.mantech.co.za/ProductInfo.aspx?Item=72M3626• Relay: EDR101A1200Z - http://www.mantech.co.za/ProductInfo.aspx?Item=35M1045• Diode: 1N4007: http://www.mantech.co.za/ProductInfo.aspx?Item=64M0027

Extras:

• 26pin IDC ribbon cable crimp connector - http://www.mantech.co.za/ProductInfo.aspx?Item=14M8762• Ribbon cable - http://www.mantech.co.za/ProductInfo.aspx?Item=45M0001• Single core cable• Veroboard - http://www.mantech.co.za/ProductInfo.aspx?Item=64M0010

Building the Internet of Thingswith Raspberry Pi

ReferencesInput Circuit design:http://raspberrypihobbyist.blogspot.com/2012/09/gpio-input-circuit_19.html

Output Circuit design:http://raspberrypihobbyist.blogspot.com/2012/10/revision-to-relay-circuit.html

RPi.GPIO wikihttp://sourceforge.net/p/raspberry-gpio-python/wiki/Home/

Raspberry Pi Technical Infohttp://elinux.org/RPi_Low-level_peripherals

GPIO quick referencehttp://raspi.tv/2014/rpi-gpio-quick-reference-updated-for-raspberry-pi-b

Exit Cleanlyhttp://raspi.tv/2013/rpi-gpio-basics-3-how-to-exit-gpio-programs-cleanly-avoid-warnings-and-protect-your-pi

Building the Internet of Thingswith Raspberry Pi

Neil Broers

@nbroers

neil@foo.co.za github.com/nbroers

Building the Internet of Thingswith Raspberry Pi