# micro:bit MicroPython Cookbook (Updating)

![1](https://user-images.githubusercontent.com/44191076/79871966-c0ae8b00-8417-11ea-8255-cbc681d12b8d.jpg)

[BBC micro:bit MicroPython documentation](https://microbit-micropython.readthedocs.io/en/latest/index.html#)

This is the collection of my notes, tricks and experiments about BBC micro:bit and MicroPython.

## Easer Eggs

Enter the following codes in [REPL](https://microbit-micropython.readthedocs.io/en/latest/devguide/repl.html):

```python
import this
import love
import antigravity
```

The result from <b>import this</b> is a version of [Zen of Python](https://www.python.org/dev/peps/pep-0020/) and <b>import antigravity</b> is from [original Python easter egg](https://xkcd.com/353/).

Also you can try

```python
this.authors()
love.badaboom()
```

## Some Lesser Known Facts

Since both Python and MicroPython are interpreted languages, they eat a lot of memory. Also, the hex file generated by micro:bit Python editors are consisted of 2 parts: the MicroPython firmware (up to 248 KB) and user's script (up to only 8 KB). See [Firmware Hex File](https://microbit-micropython.readthedocs.io/en/latest/devguide/hexformat.html). Which means it's less likely to build bigger projects with micro:bit's MicroPython.

One way to "minimize" your script size is to use 1-space indents instead of 4.

micro:bit's MicroPython is based on Python 3.4. Which means many built-in Python advanced feaetures, like string.format(), list comprehension, list slice, variable unpacking, lambda function, decorators, generators, @classmethod, @staticmethod, etc. can be used as well.

Also, about how micro:bit get its own version of MicroPython: [The Story of MicroPython on the BBC micro:bit](http://ntoll.org/article/story-micropython-on-microbit) by Nicholas H. Tollervey, who also created the [Mu editor](https://codewith.mu/).

## Editor of Choice

The official [Python online editor](https://python.microbit.org/v/2.0) does not need installation and can be used anywhere with Internet and Chrome web browser. Support Web-USB. It's ok to use, really.

Personally, I would perfer [Mu editor](https://codewith.mu/) for any beginners. It has code check, (limited) auto-complete and can automatically detect/upload code to your micro:bit.

If you have experiences with MicroPython with ESP8266/ESP32 or CircuitPython, you can consider [Thonny](https://thonny.org/) which allows you to access micro:bit's REPL directly without having to upload hex file.

## Why You Shouldn't Use * For Import

The following import statement

```python
from microbit import *
```

is a bad idea. This imports everything of the microbit module even you don't need many of the features and wastes extra memory.

Instead, you should only import sub-modules you are going to use:

```python
from microbit import pin0, display, sleep
```

## How Much Memory Left?

```python
from micropython import mem_info

print(mem_info(1))
```

You can also try to turn on garbage collection if the memory is almost full:

```python
import gc

gc.enable() # auto memory recycle
gc.collect() # force memory recycle
```

## Fill LED Display

Light up every LEDs. Use fillScreen() as default.

```python
from microbit import display, Image, sleep

def fillScreen(b = 9):
    f = (str(b) * 5 + ":") * 5
    display.show(Image(f[:len(f)-1]))


while True:
    
    for _ in range(2):
        fillScreen()
        sleep(100)
        fillScreen(0)
        sleep(100)
    
    for i in range(9):
        fillScreen(i)
        sleep(50)
        
    for i in reversed(range(9)):
        fillScreen(i)
        sleep(50)
```

## A More Convenient Pin Class

Make a Pin class to "rename" existing pin methods.

```python
from microbit import pin0, pin2, sleep

class Pin:
    
    __slots__ = ["pin"]
    
    def __init__(self, pin):
        self.pin = pin
    
    def set(self, value):
        self.pin.write_digital(value)
    
    def setPWM(self, value):
        self.pin.write_analog(value)
    
    def get(self):
        self.pin.set_pull(self.pin.PULL_DOWN)
        return self.pin.read_digital()
    
    def pressed(self):
        self.pin.set_pull(self.pin.PULL_UP)
        return not self.pin.read_digital()
        
    def getADC(self):
        return self.pin.read_analog()


led = Pin(pin0)
button = Pin(pin2)

while True:
    led.set(button.pressed())
    sleep(50)
```

## Another Version of Pin Class

Use **namedtuple** as a simple Pin class. Save more memory than regular class.

```python
from microbit import pin0, pin2, sleep
from ucollections import namedtuple

Pin = namedtuple('Pin', ['set', 'get'])

def setPin(pin, pull_up=False):
    pin.set_pull(pin.PULL_UP if pull_up else pin.PULL_DOWN)
    return Pin(pin.write_digital, pin.read_digital)


led = setPin(pin0)
button = setPin(pin2, pull_up=True)

while True:
    led.set(not button.get())
    sleep(50)
```

## LED Bar Graph

A 25-level LED progress bar.

```python
from microbit import display, sleep

def plotBarGraph(value, maxValue, brightness=9):
    bar = value / maxValue
    valueArray = ((0.96, 0.88, 0.84, 0.92, 1.00), 
                  (0.76, 0.68, 0.64, 0.72, 0.80),
                  (0.56, 0.48, 0.44, 0.52, 0.60), 
                  (0.36, 0.28, 0.24, 0.32, 0.40), 
                  (0.16, 0.08, 0.04, 0.12, 0.20))
    for y in range(5):
        for x in range(5):
            display.set_pixel(x, y, 
                brightness if bar >= valueArray[y][x] else 0)


while True:
    lightLevel = display.read_light_level()
    plotBarGraph(lightLevel, 255) # or plotBarGraph(lightLevel, 255, 9)
    sleep(50)
```

Since read_light_level() uses LEDs themselves as light sensors (see [this video](https://www.youtube.com/watch?v=TKhCr-dQMBY)), in this example a short delay is added, but the LED screen would still flicker a bit.

## Servo Control

```python
from microbit import pin0, sleep

def servoWrite(pin, degree):
    pin.set_analog_period(20)
    pin.write_analog(round((degree * 92 / 180 + 30), 0))


servoPin = pin0

while True:
    servoWrite(servoPin, 0)
    sleep(1000)
    servoWrite(servoPin, 180)
    sleep(1000)
```

Do not use servos and buzzers at the same time. They require different PWM frequencies and most microcontrollers can only set one frequency accross all pins at a time.

Also: micro:bit's power output may just (barely) enough to power a single SG90 mini servo. External power supply recommended.

## Value Mapping

Translate a value in a range to its corresponding value in anoher range. Borrowed from [here](https://stackoverflow.com/questions/1969240/mapping-a-range-of-values-to-another).

```python
def translate(value, leftMin, leftMax, rightMin, rightMax):
    leftSpan = leftMax - leftMin
    rightSpan = rightMax - rightMin
    valueScaled = float(value - leftMin) / float(leftSpan)
    return rightMin + (valueScaled * rightSpan)
```

## Get Pitch and Roll Degrees

These function cannot tell if the board is facing up or down. Probably need to use accelerometer.get_z() for that.

```python
from microbit import accelerometer, sleep
import math

def rotationPitch():
    return math.atan2(
            accelerometer.get_y(), 
            math.sqrt(accelerometer.get_x() ** 2 + accelerometer.get_z() ** 2)
            ) * (180 / math.pi)

def rotationRoll():
    return math.atan2(
            accelerometer.get_x(), 
            math.sqrt(accelerometer.get_y() ** 2 + accelerometer.get_z() ** 2)
            ) * (180 / math.pi)


while True:
    print("Pitch:", rotationPitch(), " / roll:", rotationRoll())
    sleep(100)
```
## NeoPixel Rainbow/Rotation

This code needs at least 3 LEDs in the NeoPixel chain. Of course, you can set a number (much) higher than actual LEDs to get smooth rainbow effects.

```python
from microbit import pin0, sleep
from neopixel import NeoPixel
from micropython import const

led_num = const(12)
led_maxlevel = const(64) # max 255
led_pin = pin0

np = NeoPixel(led_pin, led_num)

def showRainbow():
    change_amount = int(led_maxlevel / (led_num / 3))
    index = (0, int(led_num / 3), int(led_num / 3 * 2))
    for i in range(led_num):
        color = [0, 0, 0]
        for j in range(3):
            if abs(i - index[j]) <= index[1]:
                color[j] = led_maxlevel - abs(i - index[j]) * change_amount
                if color[j] < 0:
                    color[j] = 0
        if i >= index[2]:
            color[0] = led_maxlevel - (led_num - i) * change_amount
            if color[0] < 0:
                color[0] = 0
        np[i] = tuple(color)
    np.show()

def ledRotate():
    tmp = np[led_num - 1]
    for i in reversed(range(1, led_num)): # clockwise
        np[i] = np[i - 1]
    np[0] = tmp
    np.show()


showRainbow()

while True:
    ledRotate()
    sleep(50)
```

## HC-SR04 Ultrasonic Sensor

Get detected distance from HC-SR04/HC-SR04P sonar sensors. Set the parameter unit to 'cm' or 'inch'. External power supply recommended.

```python
from machine import time_pulse_us
from utime import sleep_us
from microbit import pin1, pin2, display, Image, sleep

def sonar(trig_pin, echo_pin, unit='cm'):
    
    trig_pin.write_digital(0)
    sleep_us(2)
    trig_pin.write_digital(1)
    sleep_us(10)
    trig_pin.write_digital(0)
    
    while echo_pin.read_digital() == 0:
        pass
    
    duration = time_pulse_us(echo_pin, 1, 30000)
    
    if unit == 'cm':
        return duration / 2.0 * 0.03313
    elif unit == 'inch':
        return duration / 2.0 * 0.01304
    else:
        return duration


while True:
    
    distance = sonar(trig_pin=pin1, echo_pin=pin2, unit='cm')
    print(distance)
    
    if 2 <= distance <= 20:
        display.show(Image.YES)
    else:
        display.clear()
    
    sleep(100)
```