Learning to code for robots: a six-week path

Who this is for

You are new to robotics, and maybe new to programming. You have, or will buy, a beginner microcontroller board (an Arduino-style board is a common choice), a USB cable, a breadboard, a few LEDs and resistors, a push button and a simple sensor. Check current prices and specifications on the seller's page.

The plan at a glance

1. 1.Week 1: output. Blink an LED.
2. 2.Week 2: input. Read a button.
3. 3.Week 3: variables and loops. Count presses and blink that many times.
4. 4.Week 4: analog output. Fade an LED.
5. 5.Week 5: serial monitor and analog input. Print a sensor value.
6. 6.Week 6: decisions. Turn something on when a reading crosses a threshold.

Step by step

1. 1. Keep one concept per week

   Resist the urge to jump ahead. If you finish early, repeat the week's project in a new way, such as a different blink pattern, rather than adding a new idea.

2. 2. Build and test every week

   Finish each week by running the project on the board. A program you have only read has not taught you what it does.

3. 3. Change one thing at a time

   When something breaks, undo your last change. When it works, change one number and predict what will happen before you run it.

4. 4. Keep a notebook

   Write down the pin numbers you used, what you expected and what happened. Next week you will not remember.

5. 5. Use low-voltage power only

   Power the board from USB or a small battery pack, and never connect it to mains power.

Worked example: six weekly projects

Weeks 1 and 2: blink and button

Week 1 teaches pinMode, digitalWrite and delay. Week 2 adds digitalRead, so a program can ask a question and answer it.

const int LED = 13;
const int BUTTON = 2;

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

void loop() {
  // with INPUT_PULLUP, a pressed button reads LOW
  if (digitalRead(BUTTON) == LOW) {
    digitalWrite(LED, HIGH);
  } else {
    digitalWrite(LED, LOW);
  }
}

Weeks 3 and 4: counting and fading

In week 3, store a count in a variable and use a for loop to blink that many times. In week 4, use analogWrite(pin, value) with a value from 0 to 255. On many boards this is pulse-width modulation: the pin switches on and off quickly, and the value sets how long it is on in each cycle. A value of 128 is about half on, since 128 ÷ 255 = 0.50.

Weeks 5 and 6: read a sensor and decide

A common analog input converts a voltage between 0 and 5 V into a whole number from 0 to 1023 (a 10-bit reading, which is 1024 steps). Print it with Serial.println, then convert it back to volts by hand to be sure you understand it.

const int SENSOR = A0;
const int LED = 13;

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

void loop() {
  int raw = analogRead(SENSOR);
  float volts = raw * 5.0 / 1023.0;
  Serial.print(raw);
  Serial.print(" -> ");
  Serial.println(volts);
  digitalWrite(LED, raw > 600 ? HIGH : LOW);
  delay(200);
}

Check the conversion by hand. A reading of 512 gives 512 × 5 ÷ 1023 = 2.50 V, almost exactly halfway, as it should be. A reading of 600 gives 600 × 5 ÷ 1023 = 2.93 V, so the LED lights when the sensor voltage is above about 2.9 V. That is the first real robot behavior: a measured number controls an action. A light sensor, a potentiometer or a distance sensor can all stand in as the input, as long as you check the sensor's own documentation for its voltage range.

If something goes wrong

• The upload fails. Check the selected board and port in your editor, try another USB cable and unplug other devices.
• The LED never lights. LEDs only work one way round. Flip it, and check that it has a resistor in series.
• The button seems to flicker. Mechanical switches bounce. Add a short delay after a press, or read it only when the state changes.
• The sensor value is stuck at 0 or 1023. Check the wiring of power, ground and signal, and whether the sensor really outputs a voltage in range.
• You are stuck for over an hour. Make the smallest program that shows the problem and ask a person or a forum with that code attached.

Keep it going

Before moving on, reread your notebook and pick the project you found hardest. Redo it from a blank file without looking, which shows you what has stuck and what has not. After week 6, join your sensor to a robot: drive a motor when the reading crosses a line, which is how a robot stops before a wall. Read about electronics basics so you can pick resistors with confidence, and about building your first robot in a weekend. If you hit an error message you do not understand, you can ask DuckyHelper out loud while you keep the editor open, and it can see the code on your screen.