The Shop on the Corner
The door sticks, then gives. Inside it smells of dust, old electronics and oil — a tech shop that has not been opened in years, and the last place in Neon City that belonged to Dr. Ezekiel.
This is where Kai starts. Not because it is safe, but because it is the only corner of the city that Sintech has forgotten about, and because somewhere on these shelves is everything needed to finish his grandfather's work.
Orion does not let him settle in. There are people out there — the Resistance — who need to know what Sintech is doing, and no way to reach them. Not a phone, not a message; anything on the network is read before it arrives. What they need is something that cannot be intercepted because it is not on any network at all.
"We'll begin with something simple, Kai. Let's use the Raspberry Pi Pico W to make an LED blink. This will be our beacon to contact the Resistance."
That is today's job, and it is smaller than it sounds: one light, turning on and off, on purpose. Everything else in this course is built on top of it.
The Emergency Kit
There is a box in the shop with the essentials in it. You need four things out of it, and Orion talks you through them because he cannot pick any of them up — being a drone, he has no fingers, a fact he brings up often.
The Raspberry Pi Pico W is the small board with a USB port at one end — in Orion's words, an older version of him that cannot talk, but understands MicroPython. The LED is the little light bulb with two legs of different lengths. The 220Ω resistor is the cylinder with coloured bands, there to limit how much current reaches the LED. And the breadboard is the slab of holes that lets you connect all of it without soldering.
Leave the jumper wires in the box. Tonight you do not need them — Orion is in a hurry, and this circuit is small enough to build without a single one.
Which cylinder is the 220Ω one?
Read the coloured bands. Five bands means red, red, black, black, brown; four bands means red, red, brown, gold. In this kit they are also bundled and labelled in brown tape — the doctor's eyesight was going, so he labelled everything he owned.
If you have not put MicroPython onto your Pico or set up a way to send it code yet, stop here and do Day 0 first. It takes about twenty minutes, you only ever do it once, and nothing below will work without it.
Building the Beacon
The whole circuit. One LED, one resistor, no jumper wires.
- Push the Pico into the breadboard at the very edge, so the USB port hangs off the end with room for the cable. Line the pins up with the holes and press down firmly — it takes a bit of force — but watch that none of the little pins fold under instead of going in.
- Take the LED and put its longer leg into the row beside physical pin 20.
- Put its shorter leg into a row along the blue line at the edge of the breadboard. That entire strip is joined together internally and is used as the ground rail.
- The ground rail is not actually connected to anything yet. Bridge it to any GND pin on the Pico using the 220Ω resistor. Resistors are not fussy about direction, so either way round is fine.
Trace the loop with your finger and it should make sense: current leaves pin 20, runs through the LED, along the ground rail, through the resistor and back into the Pico's ground pin. A complete circle. If any part of that ring is missing, nothing lights.
The LED only works one way round.
It is polarised — the longer leg is positive (the anode) and the shorter leg is negative (the cathode). Put it in backwards and nothing breaks, it simply stays dark, which is why this is the first thing to check when an LED refuses to light. It is the answer about half the time.
Pin 20, GP15, and Why Both Are True
Here is the one thing that trips up everybody on their first evening. You just put the LED into physical pin 20 — count the pins down the side of the board and it is the twentieth. But when you write the code in a moment, you will refer to that same pin as GP15.
Both are correct. The physical number is where it sits on the board; the GP number is what the chip calls it. Your fingers use one, your code uses the other, and the map between them is worth keeping open in a tab for the next few days:
Physical pin numbers run down the middle; the GP names your code uses sit beside them.