micro:bit game controller with Scratch

Transcription

1 Raspberry Pi Learning Resources rpf.io/learn 1 micro:bit game controller with Scratch What you will learn By creating a micro:bit game controller with a micro:bit and your Raspberry Pi, you will learn: How to send data between the micro:bit and Scratch How to control a Scratch sprite using the micro:bit How to make a cool Spaceship game in Scratch How to create custom images to display on the micro:bit What you will need Hardware As well as a Raspberry Pi with an SD card and the usual peripherals, you ll need: x1 x1 This learning resource is provided for free by the Raspberry Pi Foundation under a Creative Commons licence. See more at raspberrypi.org/resources and github.com/raspberrypilearning.

2 2 micro:bit game controller In this resource, you ll use a micro:bit as a game controller in Scratch, and help regain control of the galaxy! Finding the USB port For the micro:bit to be able to communicate with Scratch, you need to know how the micro:bit is connected to the Raspberry Pi. With the micro:bit disconnected from the Raspberry Pi, open a terminal and type the following: ls /dev/ttya* Plug your micro:bit in via the USB cable and type the command again: ls /dev/ttya* There should be a new entry in the output, probably something like dev/ttyacm1. You need to note this down.

3 3 Setting up the micro:bit Open Python 3 (IDLE) (Menu > Programming > Python 3), create a new file (File > New File), and copy the code below into the file. Save it as rpi.py. import serial from time import sleep import scratch scr = scratch.scratch() ## THE NEXT LINE MIGHT NEED TO BE CHANGED - TYPE ls /dev/ttya* into the terminal to see which port is needed. PORT = /dev/ttyacm1 ## BAUD = s = serial.serial(port) s.baudrate = BAUD s.parity = serial.parity_none s.databits = serial.eightbits s.stopbits = serial.stopbits_one while True: data = s.readline().decode( UTF-8 ) data_list = data.rstrip().split( ) try: x, y, z, a, b = data_list scr.sensorupdate({ x : x}) scr.sensorupdate({ y : y}) scr.sensorupdate({ z : z}) scr.sensorupdate({ a : a}) scr.sensorupdate({ b : b}) except: pass s.close()

4 4 This file, once running, will listen to any data being sent out from the micro:bit, and send it over to Scratch. You may have to change this line: PORT = /dev/ttyacm1 It needs to be the same as the port you noted down earlier. Coding the micro:bit The micro:bit needs to run some code that will constantly print out its accelerometer readings and button pushes. Open mu by going to Menu > Programming > mu. Now copy the code below into the editor: from microbit import * def get_sensor_data(): x, y, z = accelerometer.get_x(), accelerometer.get_y(), accelerometer.get_z() a, b = button_a.was_pressed(), button_b.was_pressed() print(x, y, z, a, b) while True: sleep(100) get_sensor_data() You can flash this file into your micro:bit straight away.

5 5 Setting up Scratch Open Scratch on the Raspberry Pi (Menu > Programming > Scratch). Go to Sensing, then right-click on slider sensor value near the bottom of the screen and choose enable remote sensor connections from the context menu. Click on OK when the dialogue box opens. Now switch back over to Python 3 (IDLE) and press F5 to run your rpi.py script. In Scratch, you should now be able to view the values from the micro:bit s sensors. Simply click on the arrow on the slider sensor value block, choose a and then check the box:

6 6 If you repeat this for sensors b, x, y, and z, then your Scratch stage should look something like this: If you tilt the micro:bit you should see the x, y, and z values changing. Pushing the buttons will switch a and b from False to True. If the readings aren t working, check the micro:bit port again, and make sure the code is running on both the micro:bit and the Raspberry Pi. Making the assets You re going to need three new sprites for this game. Delete the cat sprite and then find a rocket sprite, a UFO sprite, and a missile sprite. You can search on the web, or even draw your own.

7 7 Import each of your sprites into Scratch: Rename the sprites by changing the name in the scripts pane: The sprites will also need to be resized. You can use the shrink sprite tool to do this: Lastly, you should rotate the rocket and missile sprite, so they both point towards the right-hand side of the screen. You can do this by editing the sprite in the costume tab and choosing the rotate tool:

8 8 Coding the rocket To code your game, you can start by adding some scripts to the rocket. Because you want the game to be able to be played over and over again, you should start it by using a broadcast block. You ll also need to make a variable called score and set it to 0 at the start of the game: To start the game, the rocket needs to be placed in the centre of the screen, pointing towards the right: Next, you need to control the rotation of the rocket. This is going to be decided by the accelerometer reading from the micro:bit, in particular from the x sensor value. At the moment, this is a value between about and 1000, so it needs to be reduced a little. Create a new variable called turn and set it as shown below:

9 9 Test out your game so far: when you tilt the micro:bit left and right, the rocket should spin around. If it s not working, try restarting the Python 3 program on your Raspberry Pi and re-flashing the micro:bit with its program. You might also have to check that the micro:bit hasn t reconnected to a different port; you can check by using the command ls /dev/ttya*. Next, you want the rocket to move. The speed can be determined by how far forwards or backwards the micro:bit has been tilted. You can use the y sensor value for this, but as before, you ll need to reduce the value a little (and in this case reverse it). Test your flight controls now by tilting the micro:bit left and right, forwards and backwards. Coding the UFO The UFO needs to start in a random location and then chase after the rocket. This is fairly easy to set up. The Scratch stage stretches from about -250 to 250 horizontally (the x-axis) and -180 to 180 vertically (the y-axis), so picking two random numbers in these ranges will enable you to position the rocket:

10 10 Next, you can use a forever loop to get the UFO to chase the rocket: In a minute, you ll code the missile to launch at the UFO. If the missile hits the UFO, the game should restart and the player s score should go up by one. A new script is needed for this: To finish off the UFO, the game needs to end if it catches the rocket:

11 11 Coding the missile To make the missile always point in the correct direction, you can make it turn exactly the same way as the rocket: Next, whenever the a button is pressed on the micro:bit, the missile should fire. To do this, you can move it to the location of the rocket, tell it to show and then move forwards until it hits either the UFO or the edge of the screen. It will need to carry on turning as it flies, otherwise the missile s rotation will become out of sync with the rocket. Test out your rocket s new ability to shoot missiles.

12 12 What next? The game has plenty of potential to be improved. Can you add in some obstacles for the rocket and UFO to avoid? You still have to find a use for the b button. Maybe this could start a turbo mode where the rocket flies faster? Could the UFO shoot a laser beam at the rocket every now and then? You can learn more about the micro:bit by visiting rpf.io/microbit. This learning resource is provided for free by the Raspberry Pi Foundation under a Creative Commons licence.find more at raspberrypi.org/resources and github.com/raspberrypilearning.

13 Raspberry Pi Learning Resources Teacher's guide rpf.io/learn The micro:bit game controller teacher's guide Objectives Understand that two devices can send data to each other using serial communication Understand that Python and Scratch can communicate with each other Implement a MicroPython program to read the accelerometer data from the micro:bit Relate accelerometer data to the motion of sprites in Scratch Experiment with physical inputs, to implement new sprite behaviours Software installation For this lesson, your students will need access to the mu IDE. To install mu, open the terminal on the Raspberry Pi and type: sudo apt-get update && sudo apt-get install mu -y They will also need the Python Scratch library. You can install this by typing the following into the terminal: sudo pip3 install --pre scratch Hardware requirements Hardware As well as a Raspberry Pi with an SD card and the usual peripherals, you ll need: x1 x1 x1 This learning resource is provided for free by the Raspberry Pi Foundation under a Creative Commons licence. See more at raspberrypi.org/resources and github.com/raspberrypilearning.