12. Radio draw

12.1. Send Drawn Image

This script acts like a simple drawing program on the microbit.
You can move around the grid by tilting the microbit, toggle LEDs on and off with A-button, and send your drawing to another microbit with the B-button.
The x and y variables represent the current position on the microbit’s LED display.
The tick variable is used to control the blinking of the current position.
The grid list represents the state of each LED on the display.
Toggle(tx, ty): toggles the state of the LED at position (tx, ty) on the grid.
The ^= operator is a bitwise XOR operation that is used here to toggle between 0 and 1.
If grid[tx][ty] is 0, grid[tx][ty] ^= 1 will set it to 1, and if grid[tx][ty] is 1, grid[tx][ty] ^= 1 will set it back to 0.
Draw(t): creates an image representing the current state of the grid and the position (x, y). The position (x, y) blinks on and off every other tick.
It starts by creating a blank image with all LEDs off.
Then it loops over each position (cx, cy) in the grid.
If grid[cx][cy] is 1, it sets the pixel at (cx, cy) to a brightness of 5 via ``img.set_pixel(cx, cy, grid[cx][cy]*5) ``.
img.set_pixel(x, y, (t % 2)*9) creates a blinking effect for the pixel at the current position, (x, y).
(t % 2) gives the remainder then t is divided by 2. (t % 2)*9) is 0 when t is even or 9 if t is odd.
The function returns the created image.
ImageString(): converts the current state of the grid into a string that can be sent over the radio.
It starts with an empty string, then loops over each position (cx, cy) in the grid.
It adds the brightness of the pixel at (cx, cy) (either 0 or 9) to the string.
After each row of the grid, it adds a colon to the string.
The resulting string represents the current state of the grid in a format that can be easily sent over the radio and interpreted by another microbit running the same script.
The accelerometer is used to change the position (x, y).
If the microbit is tilted to the left or right, x is decreased or increased.
If the microbit is tilted forward or backward, y is decreased or increased.
If the A-button is pressed, the state of the LED at the current position (x, y) is toggled.
The display is updated to show the current state of the grid and the position (x, y).
If the B-button is pressed, the current state of the grid is sent over the radio.
from microbit import *
import radio

# Choose own group in pairs 0-255
radio.config(group=8)
# Turn on the radio
radio.on()

x = 2
y = 2
tick = -1

grid = [
    [0,0,0,0,0],
    [0,0,0,0,0],
    [0,0,0,0,0],
    [0,0,0,0,0],
    [0,0,0,0,0]
    ]


def Toggle(tx, ty):
    # bitwise or swaps 0 for 1 and 1 for 0
    grid[tx][ty] ^= 1


def Draw(t):
    img = Image('00000:'*5)
    for cy in range(0,5):
        for cx in range(0,5):
            img.set_pixel(cx, cy, grid[cx][cy]*5)
    img.set_pixel(x, y, (t % 2)*9)
    return img


def ImageString():
    s = ""
    for cy in range(0,5):
        for cx in range(0,5):
            s += str(grid[cx][cy]*9)
        s += ":"
    return s


while True:
    tick +=1
    if tick==2:
        tick = 0
    # check for movement
    dx = accelerometer.get_x()
    dy = accelerometer.get_y()
    if dx > 300:
        x += 1
        sleep(200)
    if dx < -300:
        x -= 1
        sleep(200)
    if dy > 300:
        y += 1
        sleep(200)
    if dy < -300:
        y -= 1
        sleep(200)
    # keep on grid
    x = max(0, min(x, 4))
    y = max(0, min(y, 4))
    # check for button press
    if button_a.was_pressed():
        Toggle(x, y)
        sleep(200)
    # update screen
    i = Draw(tick)
    display.show(i)
    if button_b.was_pressed():
        radio.send(ImageString())
    sleep(50)
Use this code to receive the image.
from microbit import *
import radio


# Choose own group in pairs 0-255
radio.config(group=8)
# Turn on the radio
radio.on()

while True:
    incoming_message = radio.receive()
    if incoming_message:
        # print(incoming_message)
        i = Image(incoming_message)
        display.show(i)

Exercise

  1. Organise players into pairs, and set the radio group to the pair number. Design a game room with 25 desks in a 5 by 5 grid. On each of these desks, place cards of different values face down according to a drawn map. A copy of the card value maps is given to each controller in each pair. The controllers take it in turns to draw the location on the grid to go to on their microbit, directing their playing partner to cards of the highest value using the radio image sent to them. Limit the time for each player to 30 seconds. After all the cards are collected declare the winner with the highest score.

    An example of a 5 by 5 grid with card values is below.

../_images/card_draw.png