Level 1 Recap Quiz

Learning Goals 5 min

Before we touch a single new sensor, today we look back. By the end of this lesson you will be able to:

1. Recall the eight Level 1 ideas you'll re-use in nearly every Level 2 lesson — pinMode, digitalWrite, digitalRead, the for loop, if/else, custom functions, Serial, and Ohm's law.
2. Read a small sketch and predict its serial output or LED behaviour without uploading it.
3. Identify your own weak spots — every wrong answer is paired with the L1 lesson that explains it, so revising tonight is a 10-minute job, not a 10-hour one.

Warm-Up 10 min

Level 2 spends most of its time on analog: PWM, ADC, smoothing, calibration, sensors. None of that lands if Level 1's digital basics are wobbly. So today we'll pause and check.

One-minute warm-up question

Aisyah's sketch looks like this. What does it do?

void setup() {
  pinMode(13, OUTPUT);
}

void loop() {
  digitalWrite(13, HIGH);
  delay(1000);
  digitalWrite(13, LOW);
  delay(1000);
}

New Concept · Reading code with a stopwatch 20 min

The hidden skill of the next 47 lessons

Every Level 2 lesson hands you a sketch and asks "what will happen?". If you have to upload to find out, debugging takes ten times as long. If you can read the sketch and predict, you spot bugs before they bite.

The two-step trick

1. Trace setup() first. List which pins become INPUT, which become OUTPUT, and what Serial.begin was called with. This runs once.
2. Walk one full loop() pass on paper. For each line, write down what changed: pin state, variable values, serial output. After one full pass, the pattern is obvious.

Example — trace this one in your head

const int LED = 9;
int count = 0;

void setup() {
  pinMode(LED, OUTPUT);
  Serial.begin(9600);
}

void loop() {
  count = count + 1;
  Serial.println(count);
  digitalWrite(LED, HIGH);
  delay(500);
  digitalWrite(LED, LOW);
  delay(500);
}

Tracing: setup makes pin 9 an output and opens Serial at 9600 baud. First loop() pass — count goes from 0 to 1, Serial prints 1, LED on, 500 ms, LED off, 500 ms. Second pass: Serial prints 2. Pattern: one blink per second, with a counter ticking up forever.

The eight things to remember from Level 1

Worked Example · Two predict-the-output drills 20 min

Drill 1 — what does this print?

void setup() {
  Serial.begin(9600);
  for (int i = 1; i <= 5; i++) {
    Serial.println(i * 2);
  }
}

void loop() { }

Trace it line by line. The for loop starts with i = 1, condition i <= 5 is true, body prints 2. Then i = 2 → prints 4. Then 3 → 6, 4 → 8, 5 → 10. Then i = 6, condition is false, loop ends. loop() is empty so nothing else happens.

Expected Serial output

2
4
6
8
10

Drill 2 — what does this LED do?

const int LED = 9;
const int BUTTON = 2;

void setup() {
  pinMode(LED, OUTPUT);
  pinMode(BUTTON, INPUT_PULLUP);
}

void loop() {
  if (digitalRead(BUTTON) == LOW) {
    digitalWrite(LED, HIGH);
  } else {
    digitalWrite(LED, LOW);
  }
}

Trace. Pin 2 uses INPUT_PULLUP — the internal pull-up resistor holds the pin HIGH when nothing is pressed, and the button pulls it LOW when pressed (recall L01-17). So:

• Button not pressed → digitalRead = HIGH → the if is false → else branch runs → LED off.
• Button pressed → digitalRead = LOW → the if is true → LED on.

One-line summary: LED is on while the button is held down, off otherwise.

Try It Yourself · Five quick-fire questions 20 min

Read each sketch and write down your answer in your notebook. Reveal one at a time only after you've committed to an answer on paper.

int n = 3;
void setup() {
  pinMode(13, OUTPUT);
  if (n > 5) digitalWrite(13, HIGH);
  else digitalWrite(13, LOW);
}
void loop() { }

void setup() {
  Serial.begin(9600);
  for (int i = 10; i >= 7; i--) {
    Serial.println(i);
  }
  Serial.println("go!");
}
void loop() { }

10
9
8
7
go!

void setup() {
  pinMode(13, OUTPUT);
}
void loop() {
  digitalWrite(13, HIGH);
  delay(250);
  digitalWrite(13, HIGH);
  delay(250);
}

void flash(int pin, int times) {
  for (int i = 0; i < times; i++) {
    digitalWrite(pin, HIGH);
    delay(100);
    digitalWrite(pin, LOW);
    delay(100);
  }
}

void setup() {
  pinMode(13, OUTPUT);
  flash(13, 3);
  delay(500);
  flash(13, 2);
}
void loop() { }

Mini-Challenge · Three short sketches to debug 15 min

Each of the sketches below has exactly one bug. Find it, fix it on paper (no need to upload), then check your answer.

Bug 1

// Should make pin 9 an output and blink it.
void setup() {
  pinMode(9, INPUT);
}
void loop() {
  digitalWrite(9, HIGH);
  delay(500);
  digitalWrite(9, LOW);
  delay(500);
}

Bug 2

// Should print 1 then 2 then 3 then stop.
void setup() {
  Serial.begin(9600);
  for (int i = 1; i < 3; i++) {
    Serial.println(i);
  }
}
void loop() { }

Bug 3

// Should turn the LED on only when the button is held.
const int LED = 9;
const int BTN = 2;
void setup() {
  pinMode(LED, OUTPUT);
  pinMode(BTN, INPUT_PULLUP);
}
void loop() {
  if (digitalRead(BTN) == HIGH) {
    digitalWrite(LED, HIGH);
  } else {
    digitalWrite(LED, LOW);
  }
}

Recap 5 min

You don't need to memorise sketches; you need to be able to trace them. Walk setup() once, walk loop() once on paper, and the behaviour will be obvious. Tomorrow we leave plain on/off behind and meet PWM — the trick that lets one digital pin pretend to be analog. Everything in Level 2 builds on the L1 ideas you just refreshed.

Diagnostic

A quick test that tells you what you know and what you don't. Today's quiz is one — use the gaps to plan tonight's revision.

Tracing

Reading code line-by-line and writing down the value of each variable / pin after each line. Trains your eyes to spot bugs before upload.

Off-by-one

The most common loop bug. i < 5 runs four times (1,2,3,4); i <= 5 runs five times. Always count.

INPUT_PULLUP polarity

Pressed = LOW, released = HIGH. Forgetting this flips every button rule.

Homework 5 min

Self-grade tonight. Go through your in-class answers and tally:

• 5 / 5 right → well done. Skim the L01-XX references in §1 just to refresh names of functions you didn't use in the quiz.
• 3 or 4 / 5 → re-read the L01 lesson next to each wrong question. Type the sketch into the IDE and step through it one line at a time.
• 0 to 2 / 5 → spend 30 minutes tomorrow re-doing L01-08, L01-11, L01-17 and L01-20. Level 2 will be tough without them.

Bring back next class:

• Your tally on a single notebook page — "X / 5 in class, weak on Y".
• Your fix for the bug-hunt sketch you found hardest, typed into the IDE.