Signal Tower

In Band 0 the light was already built into the board. Here you build the light yourself, out of separate parts, on a breadboard. That is a much bigger step than it sounds, because now things can go wrong in two places instead of one: the code, or the wiring.

Most of the time in this band, it will be the wiring. That is normal. There is a checklist at the end that finds nearly every wiring fault, and you should learn to use it before you start guessing.

What you need

• Your Arduino board and USB cable
• The breadboard from your kit
• Three LEDs: red, yellow and green if you have them. Any three colours will do.
• Three resistors of 220 ohms. The stripes read red, red, brown. Anything from 200 up to about 470 ohms also works, and the light is just slightly dimmer.
• Seven jumper wires, the kind with a stiff pin at both ends. Kits often contain wires with a socket at one end instead. Those are for something else and will not go into a breadboard.
• Card, scissors and tape for the housing at the end

By the end you will be able to

• Explain what a breadboard does and which holes are joined to which
• Build a working light circuit and say why the resistor has to be there
• Tell the two legs of an LED apart and know which way round it goes
• Control three pins in an order you designed
• Use names instead of numbers in your code, and say what that gets you
• Find a fault in code that has no error message at all

You do not need physics for this course. You need one correct picture in your head. Get this picture right now and half the confusion later never happens.

The rope activity

This takes fifteen minutes and it is worth every one of them. Read the whole activity once before you start, so you know where it is going.

What you need

Something long and bendy that you can tie. Any of these work:

• A skipping rope
• A phone charger cable or any long cable
• A shoelace, or two shoelaces knotted together
• A strip of cloth torn from an old shirt
• String, or thin rope

For the group version you want it about as long as you are tall. For the solo version, about as long as your arm is enough.

You also need a marker: a small piece of tape, a bit of paper tied on, or a knot of a different colour. This is important, so do not skip it. It is the only way to see what the rope is actually doing.

Step one: make the loop

Tie the two ends of the rope together so it becomes a closed ring with no ends. Any knot will do as long as it holds when you pull. Two ordinary knots tied one on top of the other is plenty.

Then tie your marker onto the ring somewhere.

Step two, group version: two or three other people

Step two, solo version: on your own

Step three: the three things to try

Now that the rope is moving, do these one at a time and watch the marker each time.

The second activity: read your own badge

Your band colour is brown. Brown is the code for the number 1, and Band 1 is where you are. That is not a coincidence. Resistors carry their value written on them in coloured stripes, and the nine bands of this course are named after the first nine colours of that code.

Find the 220 ohm resistors in your kit. Look at the stripes. On most 220 ohm resistors you will see red, red, brown, then a gap, then a gold stripe. Some kits use a five-stripe version which reads red, red, black, black, brown.

Write down the stripe colours you actually see on yours. From now on, find resistors by reading them rather than by guessing from the size, because all resistors look almost the same.

If your kit came with a paper listing the parts, it will usually say which packet is which. Use it to check that you picked the right ones.

First, put it down the right way round

Everything in this band names holes by row and column, and that only works if your board is the same way round as the picture.

A breadboard is a plastic block full of small holes. Inside it, some of those holes are already joined together by metal strips you cannot see.

That is the entire idea. You push component legs and wires into holes, and any two things in the same joined group are now connected to each other. No soldering, no glue, and you can pull it apart and start again.

The only thing you have to learn is which holes are joined to which. Get that wrong and nothing works, and nothing looks wrong either.

The three rules

1. Five holes in a column are joined. Look at the middle of the board. The holes are arranged in columns. In each column, the group of five holes on one side of the middle channel is joined together. If you put a wire in one of those five and a leg in another, they are connected.
2. The long lines at the edges are joined all the way along. These are called the rails. There is usually a red line with a + beside one and a blue or black line with a − beside the other. Every hole along one rail is joined to every other hole in the same rail. Rails are for things that many parts need to share, like ground.
3. Nothing crosses the middle channel. The gap down the centre is a wall. The group of five above it and the group of five below it are separate, even though they look like they are in a line.

How we will describe holes

The columns are numbered along the long edge: column 1 is at the left-hand end when the board is in front of you the long way round, then 2, 3 and so on to the right. The rows are lettered down the short side: j i h g f above the channel, and e d c b a below it, so row j is the top row and row a is the bottom row.

So hole f5 means row f, column 5. And because f, g, h, i and j in column 5 are all one joined group, putting something in f5 is the same as putting it in j5. They are the same connection.

Not every breadboard prints the letters and numbers, and some print them the other way up. What matters is the pattern, not the labels.

Two parts, and three physical skills you will use in every band from here to the end of the course. The skills take five minutes to learn and save you hours.

The LED

LED stands for light emitting diode. It is a small light. The important thing about it is that it only works one way round. Put it in backwards and nothing happens at all. It does not break, it just does not light.

You can tell which way round it goes in two ways.

• The legs are different lengths. The long leg is the side electricity goes in. It faces the pin. The short leg is where electricity comes out. It faces ground.
• The rim is flat on one side. Look at the bottom edge of the plastic dome. One side is flat rather than round. The flat side is next to the short leg. This is useful when somebody has already trimmed the legs to the same length.

A way to remember it: long leg goes to the pin, short leg goes to ground. Say it once or twice now. It is the most common mistake in this band, so if a light does not come on, turn the LED round before you do anything else.

The resistor

A resistor slows the current down. It has no direction, so it goes in either way round.

Why an LED needs one: an LED will take as much current as it can get. Connect it straight to a pin with nothing to slow it down and it takes far more than it can handle, gets hot, and burns out in seconds. The resistor limits how much gets through, and the LED lives.

Never connect an LED without a resistor. Not even for a quick test.

Reading the stripes

All resistors look almost identical. The only way to tell them apart is the coloured stripes, so learn to read them now rather than guessing.

If your kit came with a paper listing the parts, it usually says which packet is which. Use it to check.

Why 220 ohms

A rough answer is enough for now. The board supplies 5 volts. An LED is comfortable with about 15 thousandths of an amp, which is the unit we measure current in. Working out what resistance gives roughly that lands you somewhere between 200 and 330 ohms, and 220 is a common value in that range.

You do not have to do that arithmetic to finish this course. For now, anything from 200 to about 470 ohms works fine and the light is just a little dimmer at the top end. If you ever want to work it out yourself, the sum is Ohm’s law, and it is worth looking up once you are comfortable with everything in Band 4.

The three skills

Skill one: bending the legs

This is the step nobody tells you about, and it stops more beginners than anything else.

A resistor arrives with two long straight legs pointing out sideways, like a tiny dumbbell. It will not go into a breadboard in that shape. You have to bend both legs down first.

LEDs usually do not need bending, because their legs already point down. If an LED's legs are too close together for the two holes you need, spread them apart gently, holding the plastic body, not the legs.

Skill two: pushing a part in, and knowing it went in

Skill three: taking a part out again

You will move things constantly. Doing it wrong slowly destroys your parts.

• Pull by the body, never by one leg. Pulling one leg bends it and eventually breaks it off.
• Pull straight up, rocking very slightly side to side if it is tight.
• For an LED, hold the plastic dome, not the legs.
• For a jumper wire, hold the stiff plastic end, not the soft wire. Pulling the soft part will eventually tear the wire out of its plug.

Here is the sketch for the first circuit. Read it and answer the questions before you touch anything.

int lampPin = 8;

void setup() {
  pinMode(lampPin, OUTPUT);
}

void loop() {
  digitalWrite(lampPin, HIGH);
  delay(400);
  digitalWrite(lampPin, LOW);
  delay(1600);
}

Everything here you met in Band 0, except the first line, which you saw in the worked example. int lampPin = 8; makes a name called lampPin and puts the number 8 in it. Everywhere below, lampPin means 8.

Here is what you are building. Follow the picture first, then the steps.

Now test the thing you were asked to predict

Question 3 asked what would change if the resistor were on the other side of the LED. Find out.

Here are the exact holes, so you are changing the circuit and not guessing at it. Unplug the USB first.

Same idea, three times over. The one new idea is that all three lights share a single return path back to the board.

Now read the sketch you just ran

void setup() {
  pinMode(9, OUTPUT);
  pinMode(8, OUTPUT);
  pinMode(7, OUTPUT);
}

void loop() {
  digitalWrite(9, HIGH);
  digitalWrite(8, LOW);
  digitalWrite(7, LOW);
  delay(5000);

  digitalWrite(9, HIGH);
  digitalWrite(8, HIGH);
  digitalWrite(7, LOW);
  delay(1500);

  digitalWrite(9, LOW);
  digitalWrite(8, LOW);
  digitalWrite(7, HIGH);
  delay(5000);

  digitalWrite(9, LOW);
  digitalWrite(8, HIGH);
  digitalWrite(7, LOW);
  delay(1500);
}

Look at the shape of it. There are four blocks, and every block has exactly the same form: three digitalWrite lines, then one delay.

Each block is one state. A state is one complete situation: what all three lights are doing, and for how long.

Notice that every block says something about all three lights, including the ones that should be off. That looks like extra typing. It is deliberate, and there is a question about it in the next part.

a. Follow the code by hand

Copy this table onto paper and fill it in for one full round of b1_02. Then add up the four times and say how long a complete round takes.

b. Find a fault with no error message

Open b1_04_buggy_silent.ino and upload it. It will compile with no error. It will upload with no error. The wiring is correct. And the green light never comes on.

Here is the third block of its loop:

  digitalWrite(6, HIGH);
  delay(1000);
  digitalWrite(6, LOW);

Find the fault by reading. Do not touch the breadboard. Look at the top of the sketch where the names are made, and compare.

c. Put the states in order

Imagine the four state blocks of b1_02 have been cut out and shuffled. Put them back into an order that would be safe at a real road crossing, and write one sentence saying why you chose that order.

There is more than one reasonable answer. The sentence is the part that counts.

d. Explain one line

In state 1, there is a line that says digitalWrite(8, LOW);. It switches off the yellow light. But in state 1 the yellow light is already off. So why is that line there at all?

This part contains the most useful thing in the whole band, and it is disguised as a boring task. Do it properly.

Bronze

Move the yellow light from pin 8 to pin 12. Do it in b1_02 first. Count every line you had to edit, and write the number down. Then do exactly the same job in b1_03_signal_variables.ino and write that number down too. Move the wire on your board from pin 8 to pin 12 as well, so the tower still works. (Pin 6 is deliberately left empty. Part 7b needs it that way.)

Silver

Add a warning state at the very start: all three lights on together for one second, then carry on into the normal sequence.

Gold

Make the yellow light blink three times during state 2 instead of staying on solidly, without changing how long state 2 lasts in total.

Here is the top of the second sketch. Everything below it is the same as b1_02, except that it uses these names instead of the numbers.

int redPin = 9;
int yellowPin = 8;
int greenPin = 7;

int stopTime = 5000;
int changeTime = 1500;
int goTime = 5000;

Building the housing

You do not need anything fancy. A cereal box, the side of any cardboard box, or a piece of stiff card is enough.

Test it on somebody

Find one person who was not there while you built it. Do not tell them what it is. Show it to them and ask: what do you think this is telling you?

Write down what they actually said, in their words, not what you were hoping they would say.

If they got it wrong, that is not a failure. That is a finding, and it is worth more than a working build. Write down what you would change, and if you have time, change it and test again.

Show your work

Post a photo of the tower, a video of the full sequence, and the sentence your tester said. Then look at one other person's sketch and leave them one useful comment: something you would have done differently, and why.

Code you have not seen. Answer from reading only.

int a = 10;
int b = 11;
int wait = 300;

void setup() {
  pinMode(a, OUTPUT);
  pinMode(b, OUTPUT);
}

void loop() {
  digitalWrite(a, HIGH);
  digitalWrite(b, LOW);
  delay(wait);
  digitalWrite(a, LOW);
  digitalWrite(b, HIGH);
  delay(wait);
}

1. Two LEDs are wired to pins 10 and 11. Describe in one sentence what someone watching them would see.
2. Is there ever a moment when both are lit? How can you tell from the code alone?
3. Change one line so that LED a stays on twice as long as LED b. Which line, and what does it become?
4. wait is used in two places. Name one good thing about that and one bad thing about it.
5. Somebody deletes the line pinMode(b, OUTPUT);. What are you likely to see, and why is this harder to work out than an error message?
6. Both LEDs have been put in with their long legs towards GND. What will you see, and why is this not a problem with the code?

Work down this list in order. Do not skip and do not guess. Six of the seven faults below can be seen in a photograph, which is why the first thing to do when you are stuck is photograph your board.

You can read a breadboard. You can build a circuit that works and explain why each part is in it. You have met a bug that the computer could not find for you, and you found it by reading. And you have measured for yourself why naming your numbers is worth the effort.

Before you move on, make sure you have

• Your signal tower, working and housed, with a video of the full sequence
• The sentence your tester said, in their words
• Your two numbers from Bronze
• Your completed state table from Part 7a
• Your build log for this band
• Five or six correct answers in Part 10, including question 6

Next is Band 2: Mood Lamp. So far your lights have only been fully on or fully off. Next you get everything in between, and colour.