7. Motor_with_transistor

The examples below use definition blocks to better organize the code.

7.1. Connections

The motor requires a 2.2 k ohm resistor with the transistor to power it properly using code.

The 2.2 k ohm resistor has Red, Red, Red, Gold coloured bands.

7.2. Model

Place the resistor and transistor first.
Make sure the transistor front flat edge is facing forwards.
Connect with the motor terminal block.
Connect with the jumper wires.

7.3. Write digital

To turn the motor on fully, use pin0.write_digital(1).

To turn the motor off, use pin0.write_digital(0).

7.4. Turn on and off pin0

Pressing A turns on the motor.

Pressing B turns off the motor.

from microbit import *


def turn_on():
    pin0.write_digital(1)


def turn_off():
    pin0.write_digital(0)


while True:
    if button_a.is_pressed():
        turn_on()
    elif button_b.is_pressed():
        turn_off()
    sleep(500)

Tasks

Use the turn on and turn off functions to complete these tasks.

Write code to turn on the motor for 6 seconds then turn it off for 2 seconds before repeating.
Write code to turn on the motor for 6 seconds then turn it off for 2 seconds when the A-button is pressed, and on for 2 seconds then off for 6 seconds when the B-button is pressed, and off when nothing is pressed.
Write code to turn on the motor for 6 seconds then turn it off for 2 seconds when the A-button is pressed, and on for 2 seconds then off for 6 seconds when the B-button is pressed, and on for 4 seconds then off for 4 seconds when nothing is pressed.

Tasks

Write a new function that uses the turn_on and turn-off functions and has parameters for the length of time to turn it on and the length of time to turn it off. Set both of these parameters to a default value of 4000.
Write code, using this new function, to turn on the motor for 6 seconds then turn it off for 2 seconds when the A-button is pressed, and on for 2 seconds then off for 6 seconds when the B-button is pressed, and on for 4 seconds then off for 4 seconds when nothing is pressed.

7.5. Write analog

To turn the motor on fully use pin0.write_analog(1023).
To turn the LED off use pin0.write_analog(0).
write_analog can have values from 0 to 1023.
write_analog can be used to power the motor at different speeds.

Here is some sample code making use of write_analog to change the speed of the motor.

from microbit import *


def pulse_on():
    sleep_time = 500
    step_size = 200
    for i in range(200, 1023, step_size):
        pin0.write_analog(i)
        sleep(sleep_time)
    pin0.write_analog(1023)


def pulse_off():
    sleep_time = 500
    step_size = 200
    for i in range(1023, 200, -step_size):
        pin0.write_analog(i)
        sleep(sleep_time)
    pin0.write_analog(0)


while True:
    if button_a.is_pressed():
        pulse_on()
    elif button_b.is_pressed():
        pulse_off()
    sleep(500)

Tasks

Modify the pulse_on code so it has twice as many steps. Modify the pulse_off code so each step is half as long.
Modify the pulse_on and pulse_off functions further to show the motor speed as a value from 0 to 9. Hint: write a new function, motor_speed_display, that uses the int function to round down the value obtained from dividing the motor speed by 100. Then use the min function to make sure the highest possible value returned is 9.

7.6. Scaling the readings

The analog range, from 0 to 1023, can roughly be converted to a scaled range of 0 to 9 by dividing by 100.

The expression below uses int to round down to an integer and min to keep the maximum value at 9.

min(9, int(analog_val / 100))

Converts an analog value from a range of 0 to 1023 to 0 to 9.

e.g. scaled_value = min(9, int(analog_val / 100))

Tasks

Modify the pulse_on and pulse_off code to show the motor speed as a value from 0 to 9.