Week 6 · Session 2

Lists and Hardware

Several values under one name, then a light of your own.

What a List Is

• colors = ["red", "yellow", "green"]: square brackets, items separated by commas, kept in the order written
• colors[0] is "red", colors[1] is "yellow", colors[2] is "green". Positions start at 0
• len(colors) is 3, so the last position is len(colors) - 1
• colors[3] stops with IndexError: list index out of range

Try It: Pick by Position

Run it as it is, then follow the bullets.

• Print colors[1] and colors[2]
• Print colors[3] and read the error. Which line does it point at?
• Add a fourth color and run again. What is len(colors) now, and which position is the new one at?

for Over a List

• for color in colors: hands the block "red", then "yellow", then "green"
• The name after for holds the item itself, not its position
• range hands over counts. Use it when the count is the point, and the list when the item is
• The same loop works whether the list has three items or thirty

Try It: Every Item in Turn

• Add a fourth color to the list and run again. The loop does not change
• Print "All off" once, after every color, without adding it to the list

The Pinout

GP labels sit beside each pin. Physical positions count 1 to 40 around the board.

• Pin(15, Pin.OUT) claims GP15 as an output: 3.3 volts for on, 0 volts for off. The number is the GP label, not the physical position
• Today: GP15 at position 20 and GND at position 38

The Breadboard

• Each short row of five holes is joined together under the plastic. Anything in the same row is connected
• The channel down the middle separates the left rows from the right rows
• The long strips along the edges are rails, joined end to end: red for +, blue for -
• The Pico sits across the channel, so every pin gets a row of its own

The LED and the Resistor

• An LED lets current through one way only. The long leg faces the pin, the short leg faces ground
• Backward, nothing lights and nothing breaks. Swap the legs
• The resistor keeps the current below what a pin can safely supply: 220 or 330 ohms, and it has no direction

One Light, Four Parts

Do This Now

Unplug, Then Wire One Light

• Unplug the USB cable first. Every time, before touching a wire
• Seat the Pico across the channel in rows 1 to 20, USB end at row 1
• Jumper from row 3, column j (GND) to the blue - rail beside it
• Resistor from row 20, column a (GP15) to row 24, column a
• LED across the channel: long leg in row 24, column d, short leg in row 24, column f
• Jumper from row 24, column j to the - rail

Do This Now

Light It

• In activities, New File, one_led.py
• from machine import Pin
• led = Pin(15, Pin.OUT)
• led.on()
• Plug in, wait for Board Connected in the bar along the bottom, click Run
• Still dark: flip the LED. Then check the resistor starts in row 20, not its neighbor, and both jumpers reach the - rail

Before You Leave

• One light on GP15, lit by your own code
• Leave the wiring in place. Lab 4 releases Friday and adds two more lights on GP14 and GP13
• Friday’s class is the optional Checkpoint 1 make-up, and catch up with any other work