R12-U2 · usually age 12 · Robotics Engineers

Arduino as a Controller

How does an Arduino program interact with hardware?

Pilot unit plan · 5 sessions · not yet classroom-validated

Build: Programmable LED and button

The Arduino as a controller: a sketch's setup() and loop(), digital outputs and inputs with INPUT_PULLUP, keeping time with millis() instead of waiting, and the Serial Monitor to see what the program is doing. Learners change sketches on purpose and explain each change.

Sense
Decide
Act

Who it is for

Age is a starting point, never a limit. A learner who can show what this unit starts from can begin here at any age.

How they learn: By reading and changing real Arduino sketches, predicting, testing in a model, then building and testing the real circuit.
The adult's role: An adult checks every circuit and anything that moves before it is powered.
Session: 75–90 minutes
Hardware: Arduino Uno R3 or compatible (5 V). The adult checks the power circuit and the motor driver. Motors never run from a pin; share GND between supplies.

Starts from

Ordering steps
Give step-by-step instructions in the right order, and fix a wrong step.
Built in R06-U3 Robot Instructions
If … else
Choose between two actions with 'if … else'.
Built in R08-U3 Robots That Respond
Switch inputs
Use a switch or touch as an input to a machine.
Built in R07-U3 Signals and Switches
Checking before power-on
Check polarity, current and resistor values before power-on.
Built in R12-U1 Safe Circuits and Power

Builds, and what it is the input for

Reading code
Read and change a text program: setup(), loop() and variables.
Input for R12-U3 Sensors and Actuators
Inputs and outputs in code
Read inputs and write outputs in code.
Input for R12-U3 Sensors and Actuators, R13-U1 Mobile Robot Hardware
Timing without waiting
Keep time without stopping the program (millis()).
Input for R13-U3 Autonomous Behaviour, R14-U1 Distance, Speed and Odometry, R14-U2 Feedback Control
Serial debugging
Print readings to the Serial Monitor to see what the program is doing.
Input for R12-U3 Sensors and Actuators, R13-U2 Read and React to Obstacles, R14-U1 Distance, Speed and Odometry, R14-U3 Data and Tuning

In the studio today

The labs run a model of each sketch in the browser. They prepare the real build; they never count as a working circuit.

Sessions

Session 1 · 75 min
What does a sketch do once, and what does it repeat?
setup() runs once after power-up or reset; loop() repeats. Variables. Serial.begin() and Serial.println(), and a Serial Monitor set to the same baud rate.
In the studio
- Meet the board
Hands-on
In Meet the board, predict and then watch the model of setup() once and loop() repeating. On the real board, start from Bare Minimum: print a greeting in setup() and a count in loop(), upload, and watch how fast the lines arrive. Press RESET and note what you see. Then move the count's declaration inside loop(): predict first, then test.
Starting code: Bare Minimum, from File/Examples/01.Basics/BareMinimum: an empty setup() and loop().
Evidence to collect
A prediction and the real Serial Monitor lines, annotated: which line ran once, which repeated, and why the count inside loop() never grows.
Predict
Before uploading, write which line you expect to see once and which many times.
Debug
If the Serial Monitor shows nothing or garbled text, check its baud rate against Serial.begin() before changing the code.
Reflect
In your own words: what does the board do between two runs of loop()?
⚠ Adult checks before power-on: The board sits on a non-conductive surface; nothing is wired to D0 or D1, which carry the USB serial link; the Serial Monitor uses the baud rate in Serial.begin().
Works towards: Reading code, Serial debugging
Session 2 · 75 min
How does the board switch an output?
pinMode(pin, OUTPUT), digitalWrite() HIGH (5 V) and LOW (0 V), and delay().
In the studio
- Blink an LED
Hands-on
In Blink, predict a pattern from two delay() values, then test. On the bench, with USB unplugged, move the LED from D13 to D8 and change the sketch to match: both the wire and the code must change. With a long on-time, measure the D8 jumper's breadboard row to the GND rail on DC volts, when HIGH and when LOW. Then, with USB unplugged, add a second LED on D7 and make the two take turns.
Starting code: Blink, from File/Examples/01.Basics/Blink, with LED_BUILTIN replaced by the pin you wire.
Pins
D13
LED 1 (Blink's pin, before the move)
D8
LED 1, moved
D7
LED 2
Evidence to collect
The changed sketch with each changed line explained in the learner's words, and the measured HIGH and LOW voltages.
Predict
Before each upload, write the pattern you expect from the two delay() values.
Debug
If the moved LED stays dark, check whether the wire and the sketch name the same pin before touching anything else.
Reflect
Which change needed both the wire and the code, and how will you remember that?
⚠ Adult checks before power-on: USB unplugged while moving wires; each LED has its own 220 Ω resistor in series and its short leg to GND. For the volts readings: red lead in the V/Ω socket, never 10A; probes go on breadboard rows or rails, not at the header pins.
Works towards: Inputs and outputs in code, Reading code
Session 3 · 90 min
How does the board read a button?
digitalRead(); INPUT_PULLUP and active-low (pressed reads LOW); a floating input with no pull-up.
In the studio
- Push a button
Hands-on
In Push a button, predict the reading for pressed and released, then test. On the bench, with USB unplugged, wire the button across the breadboard's gap from D2 to GND. Print digitalRead(2) to the Serial Monitor with INPUT_PULLUP, pressed and released. Then change the mode to INPUT, with the button released, and watch what the reading does. Change it back.
Starting code: InputPullupSerial, from File/Examples/02.Digital/InputPullupSerial: it reads pin 2 with INPUT_PULLUP and prints it.
Pins
D2
push button (other side to GND)
Evidence to collect
An input state table: mode × button → reading, with the INPUT case marked unreliable and the reason given.
Predict
Predict the reading for pressed and released before you press anything.
Debug
If the reading never changes, check that the button's two legs in use are diagonally opposite, then the D2 jumper's row.
Reflect
Why is a reading you cannot trust worse than no reading at all?
⚠ Adult checks before power-on: USB unplugged while wiring; the button goes between the pin and GND, never straight across 5V and GND; diagonally opposite legs are used.
Works towards: Inputs and outputs in code, Serial debugging
Session 4 · 90 min
Can the controller blink and listen at the same time?
Why delay() makes a program miss a button press, and keeping time with millis() so loop() never stops.
In the studio
- Blink an LED
- Push a button
Hands-on
With USB unplugged, build one LED on D8 blinking slowly and a button on D2 that lights a second LED on D7. First use delay(1000) for the blink: press the button ten times quickly and count how many the second LED shows. Then rewrite the blink with millis(): note the time of the last change, and toggle only when enough time has passed. Run the same ten presses.
Starting code: The learner's sketches from sessions 2 and 3, combined; for the millis() version, compare with Blink Without Delay (File/Examples/02.Digital/BlinkWithoutDelay).
Pins
D8
blinking LED
D2
push button
D7
second LED
Evidence to collect
A before/after table (presses noticed out of ten, with delay() and with millis()) and a sentence on why delay() misses presses.
Predict
Predict how many of ten quick presses the delay() version will notice.
Debug
If the millis() version never blinks, print the time and the last change to the Serial Monitor and compare them.
Reflect
Where else would a program that waits miss something important?
⚠ Adult checks before power-on: Each LED has its resistor; the button is between D2 and GND; USB unplugged while adding the second LED.
Works towards: Timing without waiting, Inputs and outputs in code
Session 5 · 90 min
Can I change a sketch on purpose, not by luck?
A latching stop button: each press flips the LED once. Edge detection, a debounce time with millis(), and Serial prints as a debugging tool.
In the studio
- Push a button
Hands-on
Start from Debounce and change it on purpose: it expects a button to 5V with a resistor to GND, but yours goes from D2 to GND, so use INPUT_PULLUP and make a press mean LOW, and point its LED at your LED on D8. Write the plan as comments first: what to remember, when a press counts, what to print. Change one thing at a time and test after each. When a press flips the LED twice, print the reading and the time to the Serial Monitor to see why, then tune the debounce time. Finally, explain one line the adult points to.
Starting code: Debounce, from File/Examples/02.Digital/Debounce (not a blank page); the learner adapts it to their own circuit.
Pins
D2
push button
D8
LED
Evidence to collect
The unit's evidence: the modified Debounce sketch, not copying blindly: every change explained in the learner's own words, the Serial lines that showed the bug, and an explanation of a line chosen by the adult.
Predict
Before changing anything, predict what Debounce will do with your button wired to GND.
Debug
When one press counts twice, print the reading and millis() for each change and find the bounce in the Serial lines.
Reflect
Which of your changes would you explain first to someone copying your sketch?
⚠ Adult checks before power-on: The button is between D2 and GND; the LED has its resistor; USB unplugged while rewiring.
Works towards: Timing without waiting, Reading code, Serial debugging

Materials

Per pair: Arduino Uno R3 (or compatible), its USB cable, and a computer with the Arduino IDE
Breadboard, jumper wires, two 5 mm LEDs, two 220 Ω resistors, a 4-leg push button
A digital multimeter (DC volts)

⚠ Safety before any session

Unplug USB before changing a wire.
Every LED has its resistor; a button goes between a pin and GND, never across 5V and GND.
Keep D0 and D1 free: on the Uno they are the serial pins used by USB.

Safety for every band

Low voltage only: battery packs or USB. Never mains electricity.
Never connect a motor straight to a controller pin: use a driver and a separate supply.
Every moving robot has a power-off switch within reach that cuts the motor battery (or all power). A software stop button is extra, never a replacement.
No coin or button cells and no loose small magnets; battery compartments screwed shut.
Guard wheels and moving parts against pinched fingers; keep robots slow and indoors.
No exposed lithium cells, improvised chargers or lasers.
No Li-ion, LiPo or RC packs: AA alkaline or NiMH cells in a closed holder with a switch, or USB.
Check polarity and voltage before power-on; a 3.3 V board must not receive 5 V signals.

Notes for the adult

Before the first upload, test an upload on each computer (Blink, with its own board and cable), so the session starts on time.
The aim is changing code on purpose: ask for a prediction before every upload, and for the reason behind every change.
A learner who already writes setup() and loop() fluently can move on to R12-U3; readiness decides, not age.
The labs run a model of each sketch; only the real board's behaviour counts as evidence here.

Planned studio features

Not built yet. The unit runs without them.

A side-by-side view of the learner's own sketch and its Serial lines for the notebook (no upload of code: kept in the browser).
Notebook pages for unit plans (today the notebook holds only the Rescue Rover course).

Sources

The facts this plan relies on, in each source's own words.

Arduino language reference: setup()
“The setup() function will only run once, after each powerup or reset of the Arduino board.”
Arduino language reference: loop()
“the loop() function does precisely what its name suggests, and loops consecutively, allowing your program to change and respond.”
Arduino built-in example: Bare Minimum
“This example contains the bare minimum of code you need for a sketch to compile properly on Arduino Software (IDE): the setup() method and the loop() method.”
Arduino built-in example: Blink (loading an example)
“start the Arduino Software (IDE) and enter the code below. You may also load it from the menu File/Examples/01.Basics/Blink”
Arduino language reference: Serial.begin()
“Sets the data rate in bits per second (baud) for serial data transmission. For communicating with Serial Monitor, make sure to use one of the baud rates listed in the menu at the bottom right corner of its screen.”
Arduino language reference: Serial.println()
“Prints data to the serial port as human-readable ASCII text followed by a carriage return character (ASCII 13, or '\r') and a newline character (ASCII 10, or '\n').”
Arduino language reference: Serial (serial pins)
“UNO R3, UNO R3 SMD Mini | 0(RX), 1(TX)”
Arduino language reference: pinMode()
“It is possible to enable the internal pullup resistors with the mode INPUT_PULLUP. Additionally, the INPUT mode explicitly disables the internal pullups.”
Arduino language reference: digitalWrite()
“If the pin has been configured as an OUTPUT with pinMode(), its voltage will be set to the corresponding value: 5V (or 3.3V on 3.3V boards) for HIGH, 0V (ground) for LOW.”
Arduino language reference: delay()
“Pauses the program for the amount of time (in milliseconds) specified as parameter. (There are 1000 milliseconds in a second.)”
Arduino: Multimeter Basics (the leads' sockets for volts)
“This will require to place the measurement selector in the Volts section the black terminal in the COM and the red terminal in the V|Ω|mA terminal.”
Arduino language reference: digitalRead()
“Reads the value from a specified digital pin, either HIGH or LOW.”
Arduino: Digital Pins (INPUT_PULLUP)
“When connecting a sensor to a pin configured with INPUT_PULLUP, the other end should be connected to ground. In the case of a simple switch, this causes the pin to read HIGH when the switch is open, and LOW when the switch is pressed.”
Arduino: Digital Pins (pins configured as INPUT)
“Often it is useful to steer an input pin to a known state if no input is present. This can be done by adding a pull-up resistor (to +5 VDC), or a pull-down resistor (resistor to GND) on the input.”
Arduino built-in example: InputPullupSerial
“The black wire connects ground to one leg of the pushbutton. The second wire goes from digital pin 2 to the other leg of the pushbutton.”
Arduino language reference: millis()
“Returns the number of milliseconds passed since the Arduino board began running the current program. This number will overflow (go back to zero), after approximately 50 days.”
Arduino built-in example: Blink Without Delay
“If the button is pressed while Arduino is paused waiting for the delay() to pass, your program will miss the button press.”
Arduino built-in example: Debounce on a Pushbutton
“Pushbuttons often generate spurious open/close transitions when pressed, due to mechanical and physical issues: these transitions may be read as multiple presses in a very short time fooling the program. … Here, the switch returns HIGH when pressed and LOW when not pressed.”

Arduino as a Controller

Who it is for

Starts from

Builds, and what it is the input for

In the studio today

Sessions

What does a sketch do once, and what does it repeat?

How does the board switch an output?

How does the board read a button?

Can the controller blink and listen at the same time?

Can I change a sketch on purpose, not by luck?

Materials

⚠ Safety before any session

Notes for the adult

Planned studio features

Sources