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The motors can be controlled by the PWM controller. The drive(PWM0, PWM1, PWM2, PWM3) function takes four values between 0 and 255. This defines the motor speed. PWM0 and PWM1 define the left motor and control the forward and reverse movement. PWM2 and PWM3 define the right motor accordingly.

The additional function stop() sets all motor movements to 0 and thus performs a braking manoeuvre.

# Import of the micro:bit module
from microbit import *

# Initialization of the I2C interface
i2c.init(freq=400000, sda=pin20, scl=pin19)

# Initialization of the PWM controller
i2c.write(0x70, b'\x00\x01')
i2c.write(0x70, b'\xE8\xAA')

# The deceleration of a motor can compensate for a different
# speed of the motors due to production-related tolerances.
biasR = 0  # Deceleration of the right motor in percent
biasL = 0  # Deceleration of the left motor in percent

# The scale function is used to rescale the bias
# variables for the calculation of the motor speed.
def scale(num, in_min, in_max, out_min, out_max):
    return (num - in_min) * (out_max - out_min) / (in_max - in_min) + out_min

# Control motors using the PWM controller
# PWM0 and PWM1 for the left motor and PWM2 and PWM3 for the right motor
def drive(PWM0, PWM1, PWM2, PWM3):
    # Scaling of the deceleration value into the value in percent
    # with which the motor should rotate.
    # Ex: bias = 5 is converted to 95
    # and then divided by 100. 255 * (95/100).
    PWM0 = int(PWM0 * (scale(biasR, 0, 100, 100, 0) / 100))
    # Repeat the procedure for all 4 channels
    PWM1 = int(PWM1 * (scale(biasR, 0, 100, 100, 0) / 100))
    PWM2 = int(PWM2 * (scale(biasL, 0, 100, 100, 0) / 100))
    PWM3 = int(PWM3 * (scale(biasL, 0, 100, 100, 0) / 100))
    # Transfer value for PWM channel (0-255) to PWM controller.
    # 0x70 is the I2C address of the controller. b'\x02 is
    # the byte for PWM channel 1. The byte with the PWM value
    # is added to the byte for the channel.
    i2c.write(0x70, b'\x02' + bytes([PWM0]))
    # Repeat the procedure for all 4 channels
    i2c.write(0x70, b'\x03' + bytes([PWM1]))
    i2c.write(0x70, b'\x04' + bytes([PWM2]))
    i2c.write(0x70, b'\x05' + bytes([PWM3]))

# stop all motors
def stop():
    drive(0, 0, 0, 0)


# Variables for the demo-while loop
speed = 35
direction = "f"

# Demo-loop
while True:

    # drive forward
    if direction == "f":
        speed += 1
        drive(speed, 0, speed, 0)
        sleep(30)
        if speed > 254:
            stop()
            print("backwards")
            sleep(1000)
            speed = 35
            direction = "b"

    # reverse
    elif direction == "b":
        speed += 1
        drive(0, speed, 0, speed)
        sleep(30)
        if speed > 254:
            stop()
            print("left")
            sleep(1000)
            speed = 35
            direction = "l"

    # Drive left
    elif direction == "l":
        speed += 1
        drive(0, speed, speed, 0)
        sleep(30)
        if speed > 254:
            stop()
            print("right")
            sleep(1000)
            speed = 35
            direction = "r"

    # Drive right
    elif direction == "r":
        speed += 1
        drive(speed, 0, 0, speed)
        sleep(30)
        if speed > 254:
            stop()
            print("forward")
            sleep(1000)
            speed = 35
            direction = "f"

    # else stop
    else:
        stop()
        print("stopped")
motor_control+bias.py