Before you start any band

Identify Which part have I got?

Two sketches that tell you what is in your hand, for the two parts in this kit that come in more than one kind.

Time: 25 min
You need: A buzzer and 2 jumper wires, or an RGB light with 3 × 220Ω resistors and 6 jumper wires
At once: Everybody at once
Before this: Nothing. Do this before Band 2, Band 3 or Band 5 if nobody has labelled your box.

Sketches for this project

Every file opens with a plain-English header saying what it does and how to wire it, hole by hole.

Why

Two parts, two kinds each

Most of what is in your box is exactly one thing. A resistor is a resistor. An LED is an LED.

Two parts are not like that. Each comes in two kinds that look almost the same and behave completely differently, and kits ship whichever kind was cheapest that month. If nobody has told you which you have, you will find out the hard way in the middle of a build.

Two sketches settle it: about ten minutes for the buzzer and fifteen for the RGB light. Do them once, write the answers on a slip of paper, and put the paper in the box.

Who needs to do this

The facilitator, once, for the whole hub, is ideal. Label the bags and nobody else ever has to think about it.

If you are working alone and nothing is labelled, do the buzzer one before Band 3 and the RGB one before Band 2. Twenty-five minutes for both, and they save you an hour of the wrong kind of confusion.

One

Which buzzer have I got?

10 min

There are two kinds of buzzer and they are the same size, the same colour, and have the same two legs.

Look first

Turn the buzzer over and look at the bottom.

Sealed underneath, often with a paper sticker on it

Almost certainly an active buzzer. There is a tiny circuit sealed inside it whose only job is to switch back and forth thousands of times a second, which is what a sound is. Because that circuit is already in there, the buzzer makes its own note: switch it on and it beeps. It knows one note, and it cannot be persuaded otherwise.

You can see a small green circuit board underneath

Almost certainly a passive buzzer. There is no such circuit inside, so it has no note of its own. Switch it on and it clicks once and then sits there. You have to do the switching back and forth yourself, from the board, which is exactly what tone does, and that is why you get to choose the note.

“Almost certainly” is not certainly, and some buzzers are sealed either way. So prove it.

Then prove it

Wire it. If one leg is longer than the other, or one is marked +, that leg goes to pin 8 and the other to the − rail. If both legs are the same length and nothing is marked, either way round works, and that on its own is a hint that yours is the passive kind, because a bare piezo disc has no right way round. Then one wire from the − rail to a GND pin.

About the resistorAn active buzzer pulls about twenty-five to thirty thousandths of an amp, and an Arduino pin is designed for twenty. Band 3, the one band that asks for an active buzzer, puts a 220 ohm resistor in its pin leg for that reason. A passive buzzer pulls far less and does not need one, which is why Bands 5, 7 and 8 wire it bare. Leaving a 220 ohm resistor in costs you a little volume and nothing else, so if you are unsure which kind you have, fit it. That is the safe direction to be wrong in.

Upload id_01_which_buzzer.ino and open the serial monitor (Tools, then Serial Monitor, 9600). Then listen while you read, because the sketch tells you what it is about to do before it does it.

Step 1 switches the pin on for a second. Step 2 asks for 440 Hz for a second. Watch which is which and listen to both.

You should seeOne of exactly two things.

It beeped both times, and both beeps sounded the same. You have an active buzzer. It made its own note in step 1, and in step 2 it ignored your request and made the same note again.

It clicked once in step 1, then played a clear note in step 2. You have a passive buzzer. There was nothing inside it to make a sound in step 1; in step 2 you gave it one.

If you heard nothing at all in either stepThe buzzer is not wired, not the buzzer. Check the long leg is on pin 8 and the − rail really reaches GND. Then swap the two legs over and try once more.

If step 2 was scratchy or rattly rather than a clean noteThat is an active buzzer being asked to do something it cannot. Count it as active.

Write it down, then read this

Band	With a passive one	With an active one
Band 3, the lock	Works, once you make two swaps. The sketch is written for an active buzzer, so change every `digitalWrite(buzzerPin, HIGH)` to `tone(buzzerPin, 1000)` and every `LOW` to `noTone(buzzerPin)`. Band 3 Part 11 stage three walks you through it.	Works as written. This is the kind Band 3 asks for.
Band 5, the game	Works fully. Four lights, four different notes.	Works, with one note instead of four. The game is still a game; you lose the pitch, which is a real loss but not a blocking one.
Band 7, the guard	Works fully. Beep rate and a rising note.	Works. You get the beep rate, which is the part that matters, and not the rising note.

If you have two buzzers, test both. Kits very often contain one of each, and if that is true of yours then nothing in this course is closed to you at all. Mark them, keep them apart, and you never think about it again.

Two

Which RGB light have I got?

15 min

This one has two questions inside it, and Band 2 needs both answered.

Question one: what shape is it?

Tip the bag out and look. You may find one of these, or both.

A loose dome with four legs, one longer than the rest

A discrete RGB LED. Three lights inside one case, sharing one leg. You fit three resistors yourself, one per colour.

→ Band 2's core build is written for this. Use it.

A small board with one light on it and a row of pins

An RGB module. The same three lights, on a board. Usually, but not always, with the three resistors already fitted.

→ Build the module Swap instead, after the check in the next box.

If you have both, build the core with the loose one first. The module afterwards takes twenty minutes and makes a good second look at the same idea.

If you have only the module, that is fine and Band 2 still works. What you would have missed is why the resistors are there, so the module page makes you go and find them on the board instead of fitting them.

Before you power a module: turn it over

Two kinds of RGB module are sold in the same kits and they look alike from the front. Only one of them has the resistors. Getting this wrong damages the light and the pin, which is exactly what the resistors were for.

Three tiny black rectangles on the back, with numbers on them

The resistors are fitted. This is the common kind.

→ Wire the three colour pins straight to Arduino pins. No resistors of your own.

A bare back, with nothing but solder and the light's own legs

This module has no resistors. Wired straight to a pin at 255 it would pull something like five times what a pin is rated for.

→ Put a 220 ohm resistor in each of the three colour wires yourself, exactly as the loose LED needs. Then carry on as normal. Write on your slip of paper that yours is the bare kind.

If you cannot tell, add the three resistors anyway. A module that already has them will simply look a little dimmer, and nothing is harmed. That is the safe direction to be wrong in, and choosing the safe direction when you are unsure is a habit worth building now.

Question two: which way round is it?

Both shapes come in two wirings, and you cannot tell by looking. This is the one you have to test.

Common cathode

The shared leg goes to ground. 0 is off and 255 is bright, which is what everything in Band 2 assumes.

Common anode

The shared leg goes to 5V. It is backwards: 0 is bright and 255 is off. Everything still works, but two things have to change: the shared leg moves to 5V, and then the numbers turn upside down in the code.

The test

Wire whichever one you have, following the wiring comment at the top of id_02_which_rgb.ino. It gives both, hole by hole.

Upload it, then open the serial monitor (click Tools, then Serial Monitor, and set the speed box at the bottom right to 9600). Watch the light while you read the words it prints. It shows red, green, blue, all-on and all-off, and names each one as it goes.

You should seeThree answers, and you want all three written down.

Which way round. If “all on” looked white and “all off” looked dark, it is common cathode and there is nothing to change. If “all on” was dark and “all off” was white, it is common anode.

Whether the colours are in the order the sketch thinks. If it said red and you saw green, your legs are in a different order. Nothing is broken.

Which pin turned out to be which colour, if they were not in order. Write the three down.

If only one colour ever lightsThe other two resistors are not making contact. Check that both legs of each are pushed right home, and that each resistor really does bridge the LED's column and the pin wire's column.

If two colours always come on together and never apartTwo colour legs are in the same column and are joined underneath. Move one. A hole takes one leg, and a column is one connection.

If nothing lights in any of the steps, including “all on”You almost certainly have a common anode part, whose shared leg wants 5V rather than ground. It is not dead. Unplug the USB cable first.

On a loose LED: take the wire running from j6 to the − rail and move that end to the + rail — the outer strip along the same top edge, the one marked with a red line and a +, not the inner one you have used all band. Then run one new wire from that same + rail to the Arduino's 5V pin. Leave the three resistors and the three pin wires exactly where they are. On a module: move the fourth pin's wire from GND to 5V.

Then check it by eye before the USB goes back in. This is the only step in the whole band that puts five volts onto the breadboard, and the one mistake that can damage the board is joining 5V to GND. So look: no wire runs from the + rail to a GND pin, and no wire runs from the − rail to 5V. If both of those are true, plug in. Run the sketch again. It will light this time, and “all on” will now be the dark one.

If it still does nothing after thatNow check the shared leg itself. On a loose LED it is the longest one, and it must be in f6. On a module it is the pin marked -, GND, VCC or +. Then check that the − rail really reaches a GND pin.

If yours is common anode, there are two steps and you need both

Everything in Band 2 still works. Do both of these, in this order.

Step one, the wiring, and it is not optional. The shared leg must go to 5V, as the box above described. A common-anode part with its shared leg on the − rail cannot light in any state at all, because the shared leg has to sit above the three colour legs for anything to flow through them. This is what Band 2 Part 12 tells you to do, and it is what makes the light work.

Step two, the numbers, and this is the part people miss. Rewiring makes it light. It does not un-invert it. With 5V on the shared leg, 255 puts five volts on both ends of the light and you get nothing, while 0 gives you full brightness. So turn every number upside down inside showColour as well:

analogWrite(redPin, 255 - r);
analogWrite(greenPin, 255 - g);
analogWrite(bluePin, 255 - b);

Subtracting from 255 undoes exactly what the hardware did, and from then on every number on every page in this course means what it says again. You can also just live with the inversion and remember that 0 is bright, which is where Band 2 Part 12 leaves you. That works, and it will catch you out about once a fortnight for the rest of the course. Write on your slip of paper which of the two you chose.

A module works exactly the same way. A module whose fourth pin is marked VCC or + is the common-anode kind: that pin goes to 5V, and its numbers are then upside down. b2_05_rgb_module.ino says the same.

Notice what just happened. It looked like a choice between a hardware fix and a software fix, and it was not: the hardware step was compulsory and it only got you half way there. That pattern is very common. The habit worth building is to ask, after any fix at all, what exactly did that change, and what did it leave alone?

The slip of paper

Write these seven things and put the paper in the box:

Buzzer 1 is active or passive
Buzzer 2 is active or passive
RGB shape: loose LED, module, or both
If a module: does it have its own resistors, or did you add three
RGB wiring: common cathode or common anode
Which pin is red, which is green, which is blue
The date, so the next person knows whether to trust it

That is twenty-five minutes now against an hour of everybody's confusion later, and it is the single highest-value thing a facilitator can do before a cohort starts.