Pibrella Workshop May 2014
Welcome to the Pibrella workshop. In this workshop you will be using the
Pibrella from Pimoroni (http://shop.pimoroni.com) and Cyntech
(http://shop.cyntech.co.uk).
The Pibrella is an addon board for the Raspberry Pi that plugs into the GPIO port
of the Pi. The Pibrella comes pre-made with 3 LEDs (Red,Green and Yellow), a
button and a simple buzzer. It also has 4 input and outputs that can be used for
other projects.
Figure 1 The Pibrella. Can you label the parts of
the Pibrella?
For this workshop you will be using Python on the Raspberry Pi to
control the LEDs, buttons and buzzer. You will also be using the
official Pimoroni Python library for controlling the Pibrella. It is
possible to control the Pibrella without using the official Python
library by accessing the GPIO directly in Python. However the official library
does a lot of the work for you in setting up and accessing the GPIO ports.
Now turn over the page to start playing with the LEDs on the Pibrella…
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Pibrella Workshop May 2014
Playing with the LED’s
The Pibrella has 3 LEDs on it, Red, Yellow and Green. In this activity you will be
learning how to switch the LEDs on and off using Python.
Project 1
In your first Python program for the Pibrella you will be switching the red LED
on and off.
Using the GPIO ports on the Raspberry Pi requires that your Python program is
run as a superuser. You will be using Idle in this session which does not normally
run in this mode. However it is possible to run Idle as a superuser so when it
runs your Python code accessing the GPIO there will be no permissions problems
(hopefully).
To run Idle in superuser mode you need to open up a terminal window and at
the command line prompt type the following:
sudo idle
Once Idle has loaded, go to File and select New Window. This will open a new
window for you to type your Python program into.
In this new window type the code from Code 1 box below:
import pibrella
import time
pibrella.light.red.on()
time.sleep(2)
pibrella.light.red.off()
import brings in Python code
from other files. In your
program you are getting code
to access the Pibrella and code
that allows you to do stuff
with time.
Code 1 Turning the red LED on and off
Once you have typed this in press F5 to run your Python program. You will be
prompted to save your code. Give your code a filename and save in your home
directory. Once done the red LED on the Pibrella will light up for 2 seconds.
Well done on completing your first Python program for the Pibrella.
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Pibrella Workshop May 2014
CHALLENGE: Can you change your program so that it lights up the Green or
Amber LEDs instead?
Question: What line would you change in your program to increase or decrease
the amount of time that the LED is on?
Project 2
Apart from switching on individual LEDs by name, the Pibrella Python library
also allows you to also perform actions on all of the LEDs at once.
You can either edit your existing program or create a new one. So either enter all
the Python code in Code 2 box below as a new program or change your existing
one to look like it.
import pibrella
import time
pibrella.light.on()
time.sleep(2)
pibrella.light.off()
Code 2 Python program to switch on all of the LEDs at once
Once you have a program that looks like the above, press F5 to run it. When the
program runs you should see all of the three LEDs come on at once.
Congratulations you can now turn on all of the LEDs at once.
CHALLENGE: Get the LEDs on the Pibrella to mimic a set of traffic lights
GOING FURTHER: The Pibrella Python library also has commands that you can
use to make the LEDs blink, fade and pulse. How could you use these? Look at the
Pimoroni GitHub page (link on last page) to find out more.
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Pibrella Workshop May 2014
Playing with the button
In this activity you are going to learn how to use the button on the Pibrella.
Project 3
Create a new window in Idle for this project, and enter the code from Code 3 box
below:
import pibrella
import time
while True:
if pibrella.button.read():
print("Button pressed")
else:
print("Button not pressed")
time.sleep(0.1)
Code 3 Python code to look for a button press
In the code above you are using a while loop to keep checking whether the
button on the Pibrella has been pressed. A loop allows you to repeat a section of
code a number of times. Which you are doing here.
This project is an illustration of “polling”. There are two main disadvantages to
“polling”. The first is that while you are checking for something to happen (in this
case the pressing of a button) you cannot do anything else.
The other disadvantage is that it is possible to miss the button being pressed.
Press F5 (if you haven’t done so already) and you will see that when you press
the button the text changes to Button Pressed and then back.
So now that you have tried “polling” let’s look at turning your program for
looking for a button press in to an event driven program! Onto project 4 on page
5.
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Pibrella Workshop May 2014
Project 4
In this project you will create a program that when you press the button makes a
noise, turns on the red LED, while counting to 100! To do all this you are going to
create an event driven program.
So as usual by now start a new window for your program, and enter the code
from the Code 4 box below:
import pibrella
import time
def button_pressed(pin):
print("You pressed the button!")
pibrella.light.red.on()
pibrella.buzzer.alarm()
time.sleep(1)
pibrella.light.red.off()
pibrella.buzzer.stop()
pibrella.button.pressed(button_pressed)
for x in range(1,100):
print (x);
Code 4 An example event driven program using the button
Ok in the program you have just entered you have created a function called
button_pressed. This function will get called everytime the button is pressed.
‘Suppose I better explain what a function is. A function allows you to reuse code
in multiple places in your program without repeating it everytime. You write it
once (as a function) and then call that function each time you want to use that
code in your program.
When you press F5 you will notice that the program starts counting from 1 to
100. When you press the button a message appears, the red LED comes on and
the buzzer plays an alarm! And the counting continues during all this!
For the counting you are using another type of loop called a for loop.
You are able to do all of the above because the function that was created was
attached to the button pressed event. Which means the function is only called
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Pibrella Workshop May 2014
when the button is pressed, so your program is free to go off and do other stuff
like count to 100.
CHALLENGE: Change the for loop so it counts from 30 to 300.
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Pibrella Workshop May 2014
Playing with the buzzer
In this activity you are going to get the buzzer on the Pibrella to work. Ok I know
technically you have already with Project 4.
Project 5
The buzzer on the Pibrella has 3 inbuilt sounds that you can call. These are fail,
success and alarm.
Once more create a new window in Idle for this project, and enter the code from
the Code 5 box.
import pibrella
import time
pibrella.buzzer.fail()
time.sleep(2)
pibrella.buzzer.success()
time.sleep(2)
pibrella.buzzer.alarm()
time.sleep(2)
pibrella.buzzer.stop()
Code 5 Inbuilt buzzer sounds on the Pibrella
Once you have done that press F5 to run and you will hear all three of the inbuilt
sounds on the Pibrella.
Remember when using the button to use the stop command to stop the buzzer
playing.
So that was easy wasn’t it? Ready to try something a little more complicated?
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Pibrella Workshop May 2014
Project 6
In this project you will play a short musical scale. I’ll apologise now this is the
sum of my musical ability, otherwise you would have some fancy tune.
You know what to do now to at the start of a project
import pibrella
import time
notes = {
'c':3830,
'd':3400,
'e':3038,
'f':2864,
'g':2550,
'a':2272,
'b':2028,
'C':1912}
tune = [notes['c'],notes['d'],notes['e'],notes['f'],notes['g']]
for x in tune:
pibrella.buzzer.buzz(x)
time.sleep(0.5)
pibrella.buzzer.stop()
Code 6 Playing a scale on the buzzer
In the code above you use a dictionary to define the frequencies of the various
notes that can be played. A list is then used to hold the notes that make up the
tune, in this example a simple scale.
After that a for loop is used to loop through each of the notes in the tune to play
them.
Press F5 to hear the tune being played on the buzzer.
QUESTION: Where else have you used a for loop in this workshop?
CHALLENGE: Create a new tune to be played by your program.
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Pibrella Workshop May 2014
WOW! Congratulations you have completed the workshop and found out how to
use the
LEDs,button
and buzzer
on the Pibrella.
Finally one to try at home with the Pibrella and Minecraft. Save this code in the
~/mcpi/api/python folder for it to work. This is a variation of Project 4 that also
sends a message to the screen in Minecraft on the Pi.
import pibrella
import mcpi.minecraft as minecraft
import time
mc = minecraft.Minecraft.create()
def button_pressed(pin):
print("You pressed the button!")
pibrella.light.red.on()
pibrella.buzzer.alarm()
time.sleep(1)
pibrella.light.red.off()
pibrella.buzzer.stop()
msg = "Button Pressed"
mc.postToChat(msg)
pibrella.button.pressed(button_pressed)
for x in range(1,100):
print (x);
Useful Pibrella Links
The Official Pibrella website is http://pibrella.com
You can get the official Pimoroni Python library for the Pibrella from GitHub at the following
web address https://github.com/pimoroni/pibrella .
The Pibrella can also be programmed using ScratchGPIO on the Raspberry Pi. You can find out
more about ScratchGPIO here http://cymplecy.wordpress.com/2013/03/19/scratch-gpiodevelopment/
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You can find a digital version of this worksheet and examples of accessing the Pibrella
directly via the GPIO on my blog Manic Coding at http://maniccoding.blogspot.co.uk