8. Potentiometer

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

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The potentiometer is a variable resistor.

Turn it one way to reduce the resistance. Turn it the other way to increase it.

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8.1. Model

1. Place the potentiometer.

2. Connect with the jumper wires.

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8.2. Read analog

To read the value of the potentiometer use pin2.read_analog.

The code below reads the value and displays it.

Try turning it from side to side to see the effect.

from microbit import *

while True:
    pot_val = pin2.read_analog()
    display.scroll(pot_val, delay=80)
    sleep(20)

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8.3. Scaling the readings

scale(value, from_, to)

Converts a value from a range to another range.

Parameters:

• value – A number to convert.

• from – A tuple to define the range to convert from.

• to – A tuple to define the range to convert to.

Returns:

The value converted to the to range.

e.g. temp_fahrenheit = scale(30, from_=(0.0, 100.0), to=(32.0, 212.0))

Tasks

1. Modify the code to scale the potentiometer value in the range 0 to 9 and scrolls its value.

Q1

Modify the code to scale the potentiometer value in the range 0 to 9 and scrolls its value.

from microbit import *

while True:
    pot_val = pin2.read_analog()
    scaled_pot_val = scale(pot_val, from_=(0.0, 1023.0), to=(0, 9))
    display.scroll(scaled_pot_val, delay=80)
    sleep(20)

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8.4. Advanced: Power meter simulation

The code below takes an analog value from the potentiometer and displays it on the microbit LEDs.

See the custom images lesson for more on display.set_pixel.

The maximum potentiometer reading is 1023, so this can be treated as 1000 for simplicity.

This gives 5 levels in steps of 200.

Each row step of 200 can be divided into 10 steps of brightness from 0 to 9.

3 variables are used for each section of the display: y_clear_list for the blank rows, y_list for the full brightness rows and y_val for the row in between that is of partial brightness.

y_clear_list has the rows which are at brightness of 0.

y_list has the rows which are at brightness of 9.

y_val is the row with variable brightness.

Each of these variables is first checked to see if it is None before setting the pixels it controls.

from microbit import *


def display_level(level):
    x_list = [0, 1, 2, 3, 4]

    # display
    val = int((level % 200) * 9 / 200)
    if level < 200:
        y_val = 4
        y_list = None
        y_clear_list = [0, 1, 2, 3]
    elif level < 400:
        y_val = 3
        y_list = [4]
        y_clear_list = [0, 1, 2]
    elif level < 600:
        y_val = 2
        y_list = [3, 4]
        y_clear_list = [0, 1]
    elif level < 800:
        y_val = 1
        y_list = [2, 3, 4]
        y_clear_list = [0]
    elif level < 1000:
        y_val = 0
        y_list = [1, 2, 3, 4]
        y_clear_list = None
    else:
        y_val = None
        y_list = [0, 1, 2, 3, 4]
        y_clear_list = None

    for x in x_list:
        if y_val is not None:
            display.set_pixel(x, y_val, val)
        if y_list is not None:
            for y in y_list:
                display.set_pixel(x, y, 9)
        if y_clear_list is not None:
            for y in y_clear_list:
                display.set_pixel(x, y, 0)


def display_potentiometer_level(pin=pin2):
    pot_val = pin2.read_analog()
    display_level(pot_val)


while True:
    display_potentiometer_level()
    sleep(20)