6. Radio resend

6.1. Back and forth messaging

The code below creates a continuous conversation between 2 microbits that might seem like an infinite loop as the messages might be sent back and forth indefinitely.
If two microbits are running this code and one sends a message “A”, the other will receive it, display it, and then send a message “B”.
Then the first microbit will receive “B”, display it, and send “A” again.
This could go on indefinitely, but it’s controlled by the sleep(250) command which introduces a delay of 250 milliseconds between each loop iteration, preventing the system from being overwhelmed.
To stop this, introduce a condition to break the loop or turn off the microbits.

from microbit import *
import radio

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

while True:
    # send
    if button_a.was_pressed():
        radio.send("A")
    elif button_b.was_pressed():
        radio.send("B")
    # receive
    incoming_message = radio.receive()
    if incoming_message:
        display.show(incoming_message)
        sleep(250)
        if incoming_message == "A":
            radio.send("B")
        elif incoming_message == "B":
            radio.send("A")

Tasks

Add counter variables to the code to limit the number of receiver based sends to 5 for each letter.

6.2. Back and forth messaging

In summary, the code below allows two microbits to send and receive characters from the string “ABCDEFG” to each other.
When one microbit sends a character, the other microbit displays it and then sends the next character in the sequence.
If button B is pressed, it stops displaying messages and clears the radio queue.

index_next = (s.index(incoming_message) + inc) % len(s): calculates the index of the next character to be sent.
s.index(incoming_message): finds the index of the received message in the string s. For example, if s is “ABCDEFG” and the incoming message is “C”, this would return 2 (since indexing starts from 0).
+ inc: adds the increment (inc) to the index. In this code, inc is set to 1, so this effectively gets the index of the next character in the string.
% len(s): is the modulus operation, which finds the remainder of the division of the number by len(s). This is used to ensure that the index doesn’t go out of bounds. If the index reaches the end of the string, it wraps around to the start.
radio.send(s[index_next]): This line sends the character at the calculated index in the string s via radio. For example, if s is “ABCDEFG” and index_next is 3, this would send “D”.

from microbit import *
import radio

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

# Define the string
s = "ABCDEFG"
# set the index steps
inc = 1
# set the delay after showing a letter
showtime = 400

while True:
    # send
    if button_a.was_pressed():
        radio.send(s[0])   # start at start
    # receive
    incoming_message = radio.receive()
    if incoming_message is not None:
        if button_b.was_pressed():
            # Clear the radio queue by calling radio.receive()
            while radio.receive() is not None:
                sleep(100)
        else:
            display.show(incoming_message)
            sleep(showtime)
            index_next = (s.index(incoming_message) + inc) % len(s)
            radio.send(s[index_next])

Exercises

Challenge your partner to stop the display on their microbit at a certain letter by pressing B.

Tasks

Modify the code to start at a randomly chosen letter.

6.3. Speed ups

Below is code to speed up the resending with each new start via the A-button.

from microbit import *
import radio
import random  # Import the random module

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

# Define the string
s = "ABCDEFG"
# Initialize the index
inc = 1
# set the delay after showing a letter
showtime = 550

while True:
    # send
    if button_a.was_pressed():
        if showtime == 100:
            # reset delay after showing a letter
            showtime = 500
        else:
            # speed up letter display
            showtime = max(100, showtime - 50)
        # Send the showtime to all microbits
        radio.send('showtime:' + str(showtime))
        start_letter = random.choice(s)  # Choose a random letter from s
        radio.send(start_letter)  # Send the random letter
    # receive
    incoming_message = radio.receive()
    if incoming_message is not None:
        if incoming_message.startswith('showtime:'):
            # Update the showtime from the received message
            showtime = int(incoming_message.split(':')[1])
        elif button_b.was_pressed():
            # Clear the radio queue by calling radio.receive()
            while radio.receive() is not None:
                sleep(100)
        else:
            display.show(incoming_message)
            sleep(showtime)
            index_next = (s.index(incoming_message) + inc) % len(s)
            radio.send(s[index_next])

Exercises

Challenge your partner to stop the display on their microbit at a certain letter by pressing B.