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Code

A photoresistor (or light-dependent resistor, LDR, or photocell) is a light-controlled variable resistor. The resistance of a photoresistor decreases with increasing incident light intensity; in other words, it exhibits photoconductivity. A photoresistor can be applied in light-sensitive detector circuits, and light- and dark-activated switching circuits.

A photoresistor is made of a high resistance semiconductor. In the dark, a photoresistor can have a resistance as high as several megohms (MΩ), while in the light, a photoresistor can have a resistance as low as a few hundred ohms. If incident light on a photoresistor exceeds a certain frequency, photons absorbed by the semiconductor give bound electrons enough energy to jump into the conduction band. The resulting free electrons (and their hole partners) conduct electricity, thereby lowering resistance. The resistance range and sensitivity of a photoresistor can substantially differ among dissimilar devices. Moreover, unique photoresistors may react substantially differently to photons within certain wavelength bands.

A photoelectric device can be either intrinsic or extrinsic. An intrinsic semiconductor has its own charge carriers and is not an efficient semiconductor, for example, silicon. In intrinsic devices the only available electrons are in the valence band, and hence the photon must have enough energy to excite the electron across the entire bandgap. Extrinsic devices have impurities, also called dopants, added whose ground state energy is closer to the conduction band; since the electrons do not have as far to jump, lower energy photons (that is, longer wavelengths and lower frequencies) are sufficient to trigger the device. If a sample of silicon has some of its atoms replaced by phosphorus atoms (impurities), there will be extra electrons available for conduction. This is an example of an extrinsic semiconductor

Here is a typical module that you can buy

Layout

ldr_bb

Code

In this example we will display the value of the LDR. In Mu , click on the Repl button and then cover the LDR

[codesyntax lang=”python”]

from microbit import *

while True:
    x = pin0.read_analog()
    print("value " + str(x))
    sleep(1000)

[/codesyntax]

Here is another example, when the analogue value is below a certain value all the LEDs will switch on

[codesyntax lang=”python”]

from microbit import *
lights_off= Image('99999:99999:99999:99999:99999:')
lights_on= Image('00000:00000:00000:00000:00000:')

while True:
    display.show(lights_off)
    x = pin0.read_analog()
    print("value " + str(x))
    if x>300:
        display.show(lights_on)
    sleep(1000)

[/codesyntax]

Python

Microbit temperature in python

by shedboy71 26th September 2016

The BBC micro:bit does not have a dedicated temperature sensor. Instead, the temperature provided is actually the temperature of the silicon die on the main CPU.

So not a perfect measure of the temperature of a room but can be used a rough guide, you could also use this to monitor that your micro bit processor is not overheating

Code

[codesyntax lang=”python”]

from microbit import *

while True:
    sleep(5000)
    print(str(temperature())+" degrees C")

[/codesyntax]

Testing

28 degrees C
28 degrees C
28 degrees C
28 degrees C
28 degrees C
28 degrees C
28 degrees C
28 degrees C
28 degrees C
28 degrees C

Python

Micro:bit compass example in micropython

by shedboy71 26th September 2016

The micro:bit also has a compass (magnetometer)

The compass has to be calibrated before it can give accurate readings. Calibration involves moving a dot to make a circle on the matrix. Once this is complete you get a smiling face image displayed to show you that you have successfully completed the calibration.

Again you will need to click on the REPL button in the mu editor prior to flashing the micro:bit

Move the Micro:bit about and you should see different values in the console, 0 is equivalent to North

Code

[codesyntax lang=”python”]

from microbit import *

compass.calibrate()
while True:
    bearing = compass.heading()
    print(bearing)
    sleep(100)

[/codesyntax]

Further Ideas

As part of an experiment you could use the display object to display one of the corresponding images

Image.ARROW_N, Image.ARROW_NE, Image.ARROW_E, Image.ARROW_SE, Image.ARROW_S, Image.ARROW_SW, Image.ARROW_W, Image.ARROW_NW

Python

Micro:bit accelerometer Micropython example

by shedboy71 26th September 2016

The micro:bit has an accelerometer on board, you can see this in the picture below

When you flash the program, you should see a reading of the accelerometer x axis being printed at the bottom of the Mu application. You can move the Micro:bit around and the values should change

Code

[codesyntax lang=”python”]

from microbit import *

while True:
    x = accelerometer.get_x()
    print(x)
    sleep(1000)

[/codesyntax]

You can also use the get_y and get_z() methods to find out the readings on the other axes. here is an example showing this

[codesyntax lang=”python”]

from microbit import *
while True:
x = accelerometer.get_x()
y = accelerometer.get_y()
z = accelerometer.get_z()
print (“x: ” + str(x) + ” y: ” + str(y) + ” z: “+ str(z))
sleep(1000)

[/codesyntax]

Python

Random image on the Micro:bit using Micropython

by shedboy71 26th September 2016

The Image class also has the following built-in instances of itself included as its attributes (the attribute names indicate what the image represents). In this example we will randomly display an image on the led matrix when the button a is pressed

Code

[codesyntax lang=”python”]

from microbit import *

import random

image_array = [Image.HEART, Image.HEART_SMALL, Image.HAPPY, Image.SMILE, Image.SAD,
Image.CONFUSED, Image.ANGRY, Image.ASLEEP, Image.SURPRISED, Image.SILLY, Image.FABULOUS,
Image.MEH, Image.YES, Image.NO, Image.CLOCK12, Image.CLOCK11, Image.CLOCK10, Image.CLOCK9,
Image.CLOCK8, Image.CLOCK7, Image.CLOCK6, Image.CLOCK5, Image.CLOCK4, Image.CLOCK3,
Image.CLOCK2, Image.CLOCK1, Image.ARROW_N, Image.ARROW_NE, Image.ARROW_E, Image.ARROW_SE,
Image.ARROW_S, Image.ARROW_SW, Image.ARROW_W, Image.ARROW_NW, Image.TRIANGLE,
Image.TRIANGLE_LEFT, Image.CHESSBOARD, Image.DIAMOND, Image.DIAMOND_SMALL, Image.SQUARE,
Image.SQUARE_SMALL, Image.RABBIT, Image.COW, Image.MUSIC_CROTCHET, Image.MUSIC_QUAVER,
Image.MUSIC_QUAVERS, Image.PITCHFORK, Image.XMAS, Image.PACMAN, Image.TARGET, Image.TSHIRT,
Image.ROLLERSKATE, Image.DUCK, Image.HOUSE, Image.TORTOISE,Image.BUTTERFLY,
Image.STICKFIGURE, Image.GHOST, Image.SWORD, Image.GIRAFFE, Image.SKULL,
Image.UMBRELLA, Image.SNAKE]

while True:
    if button_a.is_pressed():
        display.show(random.choice(image_array))
        sleep(1000)
    else:
        display.clear()

[/codesyntax]

Python

Image examples for the Micro:bit using Micropython

by shedboy71 26th September 2016

Here we show you how to create a custom image on the led matrix, we use the Mu editor – http://codewith.mu/

[codesyntax lang=”python”]

from microbit import *
im = Image(‘99999:90009:90009:90009:99999:’)
display.show(im)

[/codesyntax]

You can vary the brightness by changing the value of the digits from 0 – 9.

[codesyntax lang=”python”]

from microbit import *
im = Image(‘99999:96369:96369:96369:99999:’)
display.show(im)

[/codesyntax]

A simple animation example

[codesyntax lang=”python”]

from microbit import *

imgs = [
Image(‘90000:00000:00000:00000:00000:’),
Image(‘00000:09000:00000:00000:00000:’),
Image(‘00000:00000:00900:00000:00000:’),
Image(‘00000:00000:00000:00090:00000:’),
Image(‘00000:00000:00000:00000:00009:’)
]

display.show(imgs, delay=1000,loop=True)

[/codesyntax]
You can also set a pixel and move it around

[codesyntax lang=”python”]

from microbit import *

img = Image('00000:00000:00900:00000:00000:')
display.show(img)
sleep(1000)

while True:
img = img.shift_up(2)
display.show(img)
sleep(1000)
img = img.shift_right(2)
display.show(img)
sleep(1000)
img = img.shift_down(2)
display.show(img)
sleep(1000)
img = img.shift_left(2)
display.show(img)
sleep(1000)

[/codesyntax]
shift_left(n)

Return a new image created by shifting the picture left by n columns.

shift_right(n)

Same as image.shift_left(-n).

shift_up(n)

Return a new image created by shifting the picture up by n rows.

shift_down(n)

Same as image.shift_up(-n).

Block Editor

LED pattern using the Microsoft Block Editor for Micro:Bit

by shedboy71 26th September 2016

Go to the micro:bit web site and follow the hyperlink to Create Code. Choose the Microsoft Block Editor and make a New Project.

Look in the Basic section for the show leds block.

Drag it into the code window and click on some of the check boxes to make a pattern. Here is our example pattern

Click the Run button in the browser and you can see a preview of the image on the right hand side of the page.

Simulations are fine but we want to see this on our Micro bit, Click on the Compile button to create a .hex file for the micro bit. You will be prompted to download the file, you can either download to your computer or straight to your Micro Bit.

The Micro Bit is similar to the MBed system in that it has an online compiler which creates hex files that you save to your computer or can save to your device as it appears as a drive on your computer, I save to my computer and drag it into my Micro Bit’s drive – just my preference

Once complete you should see the pattern on your Micro Bit

Python

MicroBit push button and display image example

by shedboy71 26th September 2016

A simple example using the 2 buttons (a and b), pressing them will display one of the built in images on th 5×5 LED display on the Micro Bit

The Image Class can display a wide variety of images, you can change these in the code below

Image.HEART

Image.HEART_SMALL

Image.HAPPY

Image.SMILE

Image.SAD

Image.CONFUSED

Image.ANGRY

Image.ASLEEP

Image.SURPRISED

Image.SILLY

Image.FABULOUS

Image.MEH

Image.YES

Image.NO

Image.CLOCK12, Image.CLOCK11, Image.CLOCK10, Image.CLOCK9, Image.CLOCK8, Image.CLOCK7, Image.CLOCK6, Image.CLOCK5, Image.CLOCK4, Image.CLOCK3, Image.CLOCK2, Image.CLOCK1

Image.ARROW_N, Image.ARROW_NE, Image.ARROW_E, Image.ARROW_SE, Image.ARROW_S, Image.ARROW_SW, Image.ARROW_W, Image.ARROW_NW

Image.TRIANGLE

Image.TRIANGLE_LEFT

Image.CHESSBOARD

Image.DIAMOND

Image.DIAMOND_SMALL

Image.SQUARE

Image.SQUARE_SMALL

Image.RABBIT

Image.COW

Image.MUSIC_CROTCHET

Image.MUSIC_QUAVER

Image.MUSIC_QUAVERS

Image.PITCHFORK

Image.XMAS

Image.PACMAN

Image.TARGET

Image.TSHIRT

Image.ROLLERSKATE

Image.DUCK

Image.HOUSE

Image.TORTOISE

Image.BUTTERFLY

Image.STICKFIGURE

Image.GHOST

Image.SWORD

Image.GIRAFFE

Image.SKULL

Image.UMBRELLA

Image.SNAKE

http://microbit-micropython.readthedocs.io/en/latest/image.html – has more information on the image class
Code

This was written using the http://codewith.mu/ python editor

[codesyntax lang=”python”]

from microbit import *

# Write your code here :-)
while True:
    if button_a.is_pressed() and button_b.is_pressed():
        display.show(Image.CONFUSED)
    elif button_a.is_pressed():
        display.show(Image.YES)
    elif button_b.is_pressed():
        display.show(Image.NO)
    sleep(100)

[/codesyntax]

Newer Posts

Older Posts

Code

Microbit RGB led examples

Microbit and LDR example

Microbit temperature in python

Micro:bit compass example in micropython

Micro:bit accelerometer Micropython example

Random image on the Micro:bit using Micropython

Image examples for the Micro:bit using Micropython

LED pattern using the Microsoft Block Editor for Micro:Bit

MicroBit push button and display image example