Presentation given at Computing at Schools (CAS) NI conference 2015: "Not so hard “hardware”-Using Raspberry Pi GPIO pins with Scratch

1. ulster.ac.uk
Not so hard “hardware”
-Using Raspberry Pi GPIO pins with Scratch
Richard Gault
PhD Researcher in Computational Neuroscience
Intelligent Systems Research Centre
Ulster University, Magee

2. Not so hard “hardware”
Contents
- Teaching through context and effective use of language
- Evolving an open ended problem
- Using the Raspberry Pi GPIO pins from Scratch
- First Project:
- Belisha Beacon
- Extending knowledge:
- Traffic Lights
- Introducing Inputs:
- Pedestrian Crossing (Pelican Crossing/Toucan Crossing)
- Extending knowledge and introducing sensors:
- Puffin Crossing

3. Teaching through Context and effective use of language
Benefits of Teaching through Context:
- Bringing learning beyond the classroom
- Encourages deeper thinking in the world around
- Develops thinking from different perspectives
Effective use of Language:
- Closes the gap between problem solving and coding
- Provides a more structured discussion for problem
solving.
- Helps to put students in the computer perspective

4. Evolving an open ended problem
All aboard ‘computing sight seeing tours’
1
2
3
4
On the tour we will have:
- Raspberry Pi/Scratch/GPIO
- Electronics/Physics/Circuit Diagrams
- Controlling Outputs using Scratch
- Sequences
- Loops: Both finite and infinite
- States and state transition
- Handling inputs using Scratch
- Modifying behaviour to evaluate understanding of concepts
- A brief glimpse at sensors

5. Getting Started
Main components
- Raspberry Pi (RPi)
(These slides are based on (RPi 1), B+ V1.2)
Setting up the RPi
Also see Chapter 1: Adventures in Raspberry Pi, Carrie Anne Philbin (Wiley
2014)
- Students should have basic experience of using Scratch
RPi 2 Model B

6. GPIO pins
- General purpose input/output (GPIO) pins can be used to
interact with the real world.
- Using these pins is completely safe, however, you
should take great care when connecting cables to the
GPIO pins on your Raspberry Pi (to protect you and the
device).
Some pins are designated as power
supply (red) and others as ground
(black). The rest can either be for an
input or an output.
Input Output

7. GPIO Pins
How do they work?
Output:
The RPi acts as both a power supply and a switch. So
when we turn a particular pin on (or set it high, or to 1) in
our code, we are turning on a switch. It will remain on until
we set the pin to be off (or set it low, or 0).

8. GPIO Pins
How do they work?
Inputs:
Inputs are a little more tricky. For our work, if enough ‘input’
(voltage) comes in then the RPi will register that there is an
input, i.e. Yes = 1, or there isn’t, i.e. No = 0.

9. Using the GPIO pins from Scratch
You cannot automatically control the GPIO pins from
Scratch.
Option 1: Pi_Scratch(Pridopia)
Option 2: ScratchGPIO
Option 3: ???
If you find other alternatives please share them with the
CAS community!

10. Getting Started with ScratchGPIO
Select the right version for you:
- For RPi 1, model B+ V1.2, I recommend using
ScratchGPIO5
- For RPi 1 models before B+ you may need to
use an earlier version
- For RPi 2 with Scratch 2.0, I recommend using
ScratchGPIO7
You can download and install the right version for
you either straight from the internet to the RPi or
first downloaded on to a memory stick and
complete installation from the memory stick onto
the RPi.
Word of Caution!
Input and Output pins are pre assigned when
starting up ScratchGPIO – You can change
inputs to outputs (and vice versa) later if
needed.
Pin naming convention ->
pin11on
pin11high
GPIO17on
GPIO17high

11. Know your pin layout!
RPi 2
also
* You can damage the RPi by plugging components in to
the wrong pins.

12. Getting started with ScratchGPIO
What’s going on?
Once you have successfully installed ScratchGPIO:
Use ScratchGPIOX …without the ‘plus’
When you open up:
From ScratchGPIO we will broadcast specific messages
that the scratch gpio handler will understand and execute
the appropriate commands.

13. Stop 1: Belisha Beacon
Zebra Crossing
Lesson based upon road safety and different types of
crossings.
What exactly is a Belisha beacon?
- “It is a flashing light”
- “The light turns on and then off”
- “The light turns on, then after a second or two it turns off”
Recipe for Belisha beacon:
Ingredients will include: A light, RPi
Instructions will include: Turn light on
Wait 1 second
Turn light off
Wait 1 second

14. Stop 1: Belisha Beacon
Ingredients

15. Stop 1:Belisha Beacon
Set up: Hardware
Connect the positive side of the LED to a resistor, and
connect the resistor to pin 11 of the RPi. Connect the
negative leg of the LED to any of the ground pins of the
RPi. (see OCR Traffic Lights Recipe)
Without Breadboard With Breadboard

16. Stop 1: Belisha Beacon
Set up: Software
Start ScratchGPIO5->Go to the control tab->Use the
‘broadcast’ blocks to communicate with GPIO pins

17. Stop 1: Belisha Beacon
Implementing our recipe

18. Stop 1: What can we really do?
Also at this stop:
Electronics->flow of electricity->voltage and current
Resistance-> Actually calculating the voltage and current->V=IR calculations
Reading resistor values->Significant figures and multiplication by 10.
1
2
3
4
Continually turn a light on and off…
-Lights on an emergency vehicle
-Notification light
-School warning sign/train crossing
-Road bollard ->Translucent/transparent/opaque materials
-Traffic lights -> more complex sequences

19. Stop 2: Traffic Lights
The problem
- First work out the traffic light sequence:
- Traffic lights recipe:
Ingredients will include 3 LEDs
(one red, one amber/yellow, one
green) and 3 resistors, jumper
cables to connect RPi to components
4.
1.
2.
3.

20. Stop 2: Traffic Lights
Set up: Hardware
See OCR traffic light recipe for set up without breadboard

21. Stop 2: Traffic Lights
Implementing our algorithm
4.
1.
2.
3.

22. Stop 2: What do we really know?
- At this stage we can still only control outputs (LEDs)
- The traffic lights can be used to assess the degree of
understanding students have on circuits, using GPIO
pins and algorithmic design.
Also at this stop:
-States and state transitions.
-Repeating sequences.
-2 or more traffic lights
1
2
3
4

23. Stop 3: Pedestrian Crossing
Pelican crossing

24. Stop 3: Pedestrian Crossing
Introducing inputs
- Now we will introduce a new element to the problem:
input!
- A button will be used to signal to the system there is a
pedestrian ready to cross
- High or low?
- Let us see what happens
when the button is pressed

25. What does your input do?
Depending on the type of switch/button and the way you
construct your circuit will dictate what your system will do
when the button is pushed.
The state of the pin will either be of value 1, or value 0.
Push
button

26. Stop 3: Pedestrian crossing
Implementation
Identifying the correct code to modify
We also need red and
green LEDs for the
pedestrians!
pin26

27. Stop 3: Pedestrian Crossing
Set up: Hardware

28. Stop 3: Pedestrian
Implementation
pin26 pin26

29. Stop 3: Pedestrian Crossing
Pelican crossing from the drivers perspective

30. Stop 3: Pedestrian Crossing
Pelican Crossing-modified sequence
pin26
pin26

31. Step 3: What do we really know?
Inputs and Outputs
Switch
Button
Microphone
LED
Buzzer
Heater
Speaker
Also at this stop:
-Toucan crossing
- Inputs vs outputs exercise (telephone)
- Pull up and pull down resistor circuits
1
2
3
4
Input
Output
Why not use the button as an input to a Scratch game – 4
buttons to move a character up/down/left/right.
Revisit the emergency vehicle -> start flashing lights with
the push of a button -> introduce sound(?)

32. Stop 4: Puffin Crossing
Sensors

33. Stop 4: Puffin Crossing
Introduction to sensors
- Sensors are used to measure physical quantities such as
temperature, light, pressure, sound and movement.
- We will be using a passive infra-red sensor which will
detect a change in motion.
- If there is a change in motion, the internal properties of
the sensor will change and thus the information being
sent to the RPi will be different than before.
- So our sensor will provide information in to our system.
- We need to test our sensor value like we did with the
button.

34. Stop 4: Puffin Crossing
Testing the PIR sensor

35. pin26
Stop 4: Puffin Crossing
Implementation (same hardware set up as Pelican crossing)
pin26
pin7

36. Stop 4: Puffin Crossing
Looking at a problem from different angles
Traffic lights and pedestrian crossings must account for every eventuality
…as do good computer programs.
This often requires you to look at a problem from various perspectives.
Therefore empathy is in an important attribute to develop to become strong
at problem solving and computing.

37. Useful Links
Components:
5mm LEDs (x20 Red, x20 green, x20 yellow, x20 blue, x20 white): £1.69*
220Ohm Resistor (x 100) : £1.49*
20cm jumper cables (x40): £1.27-£1.98*
Push buttons (x100): £3.85*
Passive IR motion detector: £3.13*
400 point breadboard : £1.79*
Breakout board (RasPIO Pro) : £9.95
Breakout board (GPIO Cobbler+T-Cobbler+Ribbon Cable+breadboard) :
£11.99 *
37 Sensor kit: £34.95*
Cost for one full project: £3.64 + £11.99(optional bread board and breakout
board)
PiStop: (Traffic lights only) £2.10 -£2.95 (depending on quantity)
*Price includes delivery

38. Useful Links
Websites:
https://www.raspberrypi.org/
http://simplesi.net/scratchgpio/
http://www.ocr.org.uk/Images/129940-recipe-card-traffic-
lights.pdf
http://fritzing.org/home/
https://www.raspberrypi.org/learning/robot-antenna/
http://camjam.me/?page_id=618

39. Acknowledgements: Ann O’Neill (Stranmillis University
College)
Web:
http://isrc.ulster.ac.uk/rgault/research.html
Email:
gault-r2@email.ulster.ac.uk
CAS:
Richard Gault (email as above)
Thank you for listening!