9

Smart backpack with wireless charging pocket

TUTORIAL

your strip. pixpin identifies the pin we’ve connected

our NeoPixel strip to, which is D0. The strip variable

creates the NeoPixel strip as an object, and sets

the brightness to .5. You can change the brightness

level as needed for the look you want. strength and

direction are variables that are used to create the

pulse effect; leave them at 0 and 10.

numpix = 34 # Number of NeoPixels

pixpin = board.D0 # NeoPixels pin

strip = neopixel.NeoPixel(pixpin, numpix,

brightness=.5, auto_write=False)

strength = 0 # blue intensity

direction = 10 # direction of intensity

In the main loop, we’ll create one more variable

for the colour BLUE. The three values inside it are for

red, green, and blue values, from 0 (no colour) to 255

(maximum colour). Set red and green at zero, and use

the variable strength for blue. By changing the value

of strength in our main loop, we’ll be able to make the

blue glow change over time.

while True:

BLUE = (0, 0, strength)

We’ll send this colour formula to the strip with:

strip.fill(BLUE)

strip.show()

time.sleep(0.03)

At this point in the loop, the colour formula has been

sent to the strip, but we won’t see it yet because the

strength variable is still set to zero. To increase the blue

colour slightly over time, we’ll add:

strength += direction

This line increases the strength value by adding the

direction value to it. On the first pass through the loop,

strength = 0 and direction = 10, so the new value

of strength would be 10. On every additional pass

through the loop, the value will increase by 10, and

the strip will show a blue glow that intensifies slowly

over time.

Next, we need to add upper and lower limits to this

function. A conditional statement will work great for

this. First, let’s say that if the strength value ever gets

all the way down to zero, it should be reset to 10. At

that point we’ll also want the intensity to stop getting

lower and start going up, so we’ll flip the direction

value to its opposite:

if strength <= 0:

strength = 10

direction = -direction

you can change up the animation with new code at

any time.

Connect the Trinket to your computer using a

micro USB cable. The Trinket will appear as a drive on

your computer called ‘CIRCUITPY’. On the drive, locate

the file called main.py. This is a text file that contains

the code running on the Trinket – to reprogram the

Trinket, we’ll edit this text file. You can edit the file

in any text editor, or download a Python code editor

like Mu. Saving the main.py file will make it run

automatically on the Trinket M0.

Open the main.py file in your text editor. If your

Trinket M0 is fresh from the Adafruit factory, it will

have demo code in it. Select all of the existing code,

and delete it – we’re going to start fresh!

The first thing we need to do is import some

libraries. These libraries contain helpers that we’ll refer

to in our code.

import time

import board

import neopixel

Next, we’ll set up some variables. These

placeholders will be useful for modifying and

troubleshooting the code later. Start with numpix, and

change the number 34 to the number of NeoPixels in

Right

Keep your sewing

tidy and you’ll

end up with a great-

looking bag

Above

A small board like the

Trinket can be hidden

almost anywhere