Challenge 0: The spark

Before you can transmit anything, each device has to run on your own computer: the LED shines in a colour you choose in your program, and the sensor reports what it sees.

Goal: On each device the LED shines in a colour your program sets, and the sensor keeps printing its four readings. Each person gets their own device running on their own laptop, and at the end you switch the LED of one device and watch the numbers of the sensor opposite change.

What is new is everything: for most of you it is the first program you write, and two tools join you for the whole project, the terminal, where you start programs, and the AI assistant, which you work with. If this takes you a while, you are not behind; most people before you had never seen a terminal either.

Six tasks, one file each: the programs build on each other, and the files are ready in your template; wherever it says TODO, your code is missing.

There are no more building blocks than these: everything you program in the project is made of instructions one after the other, repeated, and under a condition. You run each task on its own, for example with python task_3_color_cycle.py (on a Mac python3).

Below, each task has its own section with what to do, the file as it looks in your template, a few hints to unfold and a sample solution you can copy or download as a file. Open the solution only once your own version runs or you are stuck: reading a finished solution is easier than writing one yourself, and only the writing is practice.

Task 1: Light on

The LED should shine red for two seconds and then go off again.

File: task_1_light_on.py; this is how it looks in your template:

# Challenge 0, task 1: Light on
#
# You learn: calling a function and handing it values.
#
# The LED should shine red for two seconds and then go off.
#
# Run it with:  python task_1_light_on.py   (on a Mac: python3)

import time

from lifi_hardware import led

# TODO: set the LED to red
#       Hint: led.set_color(red, green, blue), each value from 0 to 255

time.sleep(2)

# TODO: switch the LED off again

# Challenge 0, task 1: Light on. A sample solution.
#
# The LED shines red for two seconds and then goes off.
#
# Run it with:  python task_1_light_on.py   (on a Mac: python3)

import time

from lifi_hardware import led

led.set_color(255, 0, 0)    # red: full red, no green, no blue

time.sleep(2)

led.off()                   # the same as led.set_color(0, 0, 0)

Task 2: Blink

The LED should blink five times, half a second on and half a second off each time, without you writing the same lines five times.

File: task_2_blink.py; this is how it looks in your template:

# Challenge 0, task 2: Blink
#
# You learn: a loop, which means doing something several times without
#            writing it several times.
#
# The LED should blink five times: half a second on, half a second off.
#
# Run it with:  python task_2_blink.py   (on a Mac: python3)

import time

from lifi_hardware import led

for i in range(5):
    # TODO: LED on, wait briefly, LED off, wait briefly
    pass

# Challenge 0, task 2: Blink. A sample solution.
#
# The LED blinks five times: half a second on, half a second off.
#
# Run it with:  python task_2_blink.py   (on a Mac: python3)

import time

from lifi_hardware import led

for i in range(5):
    led.set_color(255, 255, 255)    # on, here in white
    time.sleep(0.5)
    led.off()
    time.sleep(0.5)

Task 3: Colour cycle

The LED should show all colours from the list colors one after the other, each for one second. First add at least two colours of your own to the list.

File: task_3_color_cycle.py; this is how it looks in your template:

# Challenge 0, task 3: Colour cycle
#
# You learn: a list, and how to go through it with a loop.
#
# The LED should show all colours from the list one after the other, each for
# one second. Add at least two colours of your own to the list.
#
# Run it with:  python task_3_color_cycle.py   (on a Mac: python3)

import time

from lifi_hardware import led

colors = [
    (255, 0, 0),      # red
    (0, 255, 0),      # green
    (0, 0, 255),      # blue
    # TODO: add at least two colours of your own
]

for color in colors:
    # TODO: set this colour and wait one second
    #       Hint: the three numbers are together in color
    pass

# Challenge 0, task 3: Colour cycle. A sample solution.
#
# The LED shows all colours from the list one after the other, each for one
# second.
#
# Run it with:  python task_3_color_cycle.py   (on a Mac: python3)

import time

from lifi_hardware import led

colors = [
    (255, 0, 0),      # red
    (0, 255, 0),      # green
    (0, 0, 255),      # blue
    (255, 255, 0),    # yellow: red and green together
    (255, 0, 255),    # magenta: red and blue together
]

for color in colors:
    r, g, b = color             # take the three numbers apart
    led.set_color(r, g, b)
    time.sleep(1)

led.off()

Task 4: Measure

Every time you press Enter, the program takes one reading and prints its four values; q and Enter stop it. Measure in at least four situations and change only one thing between two readings: in room light, with your hand over the sensor, with your phone torch from far away and close up. The value c is the brightness; write it down for each situation, because you need it in task 5.

File: task_4_measure.py; this is how it looks in your template:

# Challenge 0, task 4: Measure
#
# You learn: a function that gives something back, and how to take several
#            returned values apart.
#
# Every time you press Enter, the program takes one reading; q and Enter
# stops it. Measure in at least four situations and change only one thing
# between two readings: room light, the sensor covered with your hand, the
# torch of your phone from far away, the torch close up. Write down the
# clear value c for each situation; you need these numbers in task 5.
#
# If a value sticks at 65535, the sensor is overloaded: hold the torch
# further away.
#
# Run it with:  python task_4_measure.py   (on a Mac: python3)

from lifi_hardware import sensor

print("Enter = take a reading, q and Enter = stop")
while True:
    answer = input()
    if answer == "q":
        break
    # TODO: read the sensor, take the result apart into r, g, b, c
    #       and print the four values
    #       Hint: sensor.read() gives back four numbers at once

# Challenge 0, task 4: Measure. A sample solution.
#
# Every time you press Enter, the program takes one reading; q and Enter
# stops it.
#
# Run it with:  python task_4_measure.py   (on a Mac: python3)

from lifi_hardware import sensor

print("Enter = take a reading, q and Enter = stop")
while True:
    answer = input()
    if answer == "q":
        break
    r, g, b, c = sensor.read()      # four numbers come back at once
    print("r =", r, " g =", g, " b =", b, " c =", c)

Task 5: React

The program measures all the time: when it is bright, the LED shines green, when it is dark, it shines red. It is your first program that makes a decision, and it keeps running until you stop it with Ctrl+C.

File: task_5_react.py; this is how it looks in your template:

# Challenge 0, task 5: React
#
# You learn: a condition, which means doing something different depending on
#            the situation.
#
# The program measures all the time. When it is bright, the LED shines green.
# When it is dark, it shines red. Find the right threshold yourself: put it
# between the clear value with the sensor covered and the one with the torch
# from your notes of task 4.
#
# This is your first program that makes a decision. It keeps running until
# you stop it with Ctrl+C.
#
# Run it with:  python task_5_react.py   (on a Mac: python3)

import time

from lifi_hardware import led, sensor

threshold = 0   # TODO: a value between "covered" and "torch" from task 4

print("Stop with Ctrl+C")
while True:
    r, g, b, c = sensor.read()

    # TODO: if c is greater than threshold, LED green, otherwise red

    time.sleep(0.2)

# Challenge 0, task 5: React. A sample solution.
#
# The program measures all the time. When it is bright, the LED shines green.
# When it is dark, it shines red. Stop it with Ctrl+C.
#
# Run it with:  python task_5_react.py   (on a Mac: python3)

import time

from lifi_hardware import led, sensor

# Your own number goes here. Take it from your notes of task 4: somewhere
# between the clear value with the sensor covered and the one with the torch.
# 2000 is only an example and will not fit every room.
threshold = 2000

print("Stop with Ctrl+C")
while True:
    r, g, b, c = sensor.read()

    if c > threshold:
        led.set_color(0, 255, 0)    # bright: green
    else:
        led.set_color(255, 0, 0)    # dark: red

    time.sleep(0.2)

Task 6: The human as receiver

Your program sends a random sequence of colours, and one of you writes it down without looking at the screen; then you compare. The first time this works without effort. It gets interesting when you change exactly one thing each time: send faster, use more colours, do not announce the start, send the same colour twice in a row. Write down what made it fail each time. That list is pretty much the list of problems your program will have to solve in the coming challenges, and you found it yourselves.

File: task_6_human_receiver.py; this is how it looks in your template:

# Challenge 0, task 6: The human as receiver
#
# You learn: what a receiver actually has to manage.
#
# The program sends a random sequence of colours. One of you watches and
# writes it down without looking at the screen. Afterwards you compare.
#
# Try it several times and change exactly one thing each time:
#   - send faster
#   - use more colours
#   - do not announce when it starts
#   - send the same colour twice in a row
#
# Write down what made it fail each time. This list is exactly the list of
# problems your program has to solve in the coming weeks.
#
# Run it with:  python task_6_human_receiver.py   (on a Mac: python3)

import random
import time

from lifi_hardware import led

colors = {
    "red":   (255, 0, 0),
    "green": (0, 255, 0),
    "blue":  (0, 0, 255),
    "white": (255, 255, 255),
}

names = list(colors.keys())
sequence = [random.choice(names) for _ in range(10)]

input("Receiver ready? Do not look at the screen. Press Enter. ")

for name in sequence:
    led.set_color(*colors[name])
    time.sleep(1.5)          # TODO: make this shorter and see when it breaks
    led.set_color(0, 0, 0)
    time.sleep(0.5)

print()
print("What was sent:")
print("  " + ", ".join(sequence))
print()
print("Compare this with what was written down.")

# Challenge 0, task 6: The human as receiver. A sample solution.
#
# The program sends a random sequence of colours. One of you watches and
# writes it down without looking at the screen. Afterwards you compare.
#
# The task has no single right answer: the point is to change one thing at a
# time and see when the human receiver fails. This version puts the things
# you can change at the top, so that each experiment is one changed number.
#
# Run it with:  python task_6_human_receiver.py   (on a Mac: python3)

import random
import time

from lifi_hardware import led

# What you change between two attempts, one thing at a time
ON_TIME = 1.5        # seconds a colour stays on; try 0.5, then 0.2
OFF_TIME = 0.5       # dark pause between two colours; try 0, then two equal colours meet
LENGTH = 10          # how many colours are sent
ANNOUNCE = True      # False: the sequence starts without warning

colors = {
    "red":   (255, 0, 0),
    "green": (0, 255, 0),
    "blue":  (0, 0, 255),
    "white": (255, 255, 255),
    # more colours make it harder, for example:
    # "yellow":  (255, 255, 0),
    # "magenta": (255, 0, 255),
}

names = list(colors.keys())
sequence = [random.choice(names) for _ in range(LENGTH)]

input("Receiver ready? Do not look at the screen. Press Enter. ")

if ANNOUNCE:
    print("Starting in 3 seconds ...")
time.sleep(3)

for name in sequence:
    r, g, b = colors[name]
    led.set_color(r, g, b)
    time.sleep(ON_TIME)
    led.off()
    time.sleep(OFF_TIME)

print()
print("What was sent:")
print("  " + ", ".join(sequence))
print()
print("Compare this with what was written down.")