The sender micro:bit and receiver micro:bit each have their own script, and they must be running at the same time.

• Connect two micro:bit modules to two USB ports with two USB cables.
• Open two separate browsers and navigate both to python.microbit.org.
• Use the web editor Connect buttons to set up serial connections with each micro:bit.

See Texting with Terminals if you need a reminder on how to set up the serial connection to the micro:bit modules. 

• If you are part of a class, and have been assigned a channel, make sure to adjust the script’s channel=7 to your assigned channel before you save and flash the scripts.
• Enter, save, and flash the sender script countdown_sender into the sending micro:bit.
• Enter, save, and flash the receiver script countdown_reciever into the receiving micro:bit.  It’s below the countdown_sender script.

Example Sender Script: countdown_sender

# countdown_sender

from microbit import *
import radio

radio.on()
radio.config(channel=7,length=50)

sleep(1000)

print("Countdown App")
print("micro:bit sender")

while True:
    text = input("Enter countdown start: ")
    value = int(text)
    message = input("Enter message after countdown: ")
    
    dictionary = {  }
    dictionary['start'] = value
    dictionary['after'] = message

    packet = str(dictionary)
    
    print("Send: ", packet)
    radio.send(packet)
    
    print()

Example Receiver Script: countdown_receiver

# countdown_receiver


from microbit import *
import radio

radio.on()
radio.config(channel=7,length=50)

sleep(1000)

print("Countdown App")
print("micro:bit receiver\n")

while True:
    packet = radio.receive()
    if packet is not None:
        print("Receive: ", packet)

        print()
        print("Parse: ")

        dictionary = eval(packet)

        value = dictionary['start']
        message = dictionary['after']
        
        print("value = ", value)
        print("message = ", message, "\n")
        
        while value >= 0:
            print(value)
            sleep(1000)
            value = value - 1
            
        print(message)
        
        print()

• Click the Open Terminal button in both browsers, and reset both micro:bit modules.
• Follow the prompts in the sender micro:bit’s terminal for entering the countdown start value and the message to display afterwards.
• Check the receiver micro:bot’s terminal and verify that it completes the countdown and displays the message you entered.