Students will
- Detect a new press rather than repeatedly acting while a button is held
- Represent system behavior with explicit states
- Define a reset or recovery transition
Arduino Uno R3
Build event and state logic
Distinguish an input transition from a held condition and move a system through explicit named states.
MS-PRO-RD-17ProgrammingMS-PRO-TR-19Programming
Evidence of success
- Holding the button does not advance through every state
- Each state has a named observable output
- The system can return to its defined starting state
Hardware
- Arduino Uno R3
- Momentary pushbutton
- Built-in LED or protected external LED
- Breadboard and jumper wires
Prerequisites
- Read a reliable digital input
- Control an LED
- Use conditions and variables
Before class
- Prepare a simple two- or three-state diagram
- Keep the first state machine small
- Distinguish contact bounce from held-state repetition
Reviewed connection map
Button event and visible state
- Connect the button between D8 and GND.
- The output uses the built-in LED; an external protected LED may be substituted only with a matching reviewed pin and circuit.
Build and test
- 01Observe how a held button repeats a level-based action
- 02Store the previous input and detect the HIGH-to-LOW transition
- 03Define READY, ACTIVE, and COMPLETE states
- 04Allow one event to advance each state
- 05Add a deliberate reset path and test unexpected presses
Read before uploading
Annotated Arduino sketch
const int BUTTON_PIN = 8;
enum SystemState { READY, ACTIVE, COMPLETE };
SystemState state = READY;
bool previousPressed = false;
void setup() {
pinMode(BUTTON_PIN, INPUT_PULLUP);
pinMode(LED_BUILTIN, OUTPUT);
}
void loop() {
bool pressed = digitalRead(BUTTON_PIN) == LOW;
bool newPress = pressed && !previousPressed;
if (newPress) {
if (state == READY) state = ACTIVE;
else if (state == ACTIVE) state = COMPLETE;
else state = READY;
}
digitalWrite(LED_BUILTIN, state == ACTIVE);
previousPressed = pressed;
delay(20);
}Optional engineering record
Record evidence from this lesson
Choose the prompts that help students explain predictions, evidence, debugging, and transfer. Saving creates a new entry in this browser’s Rudi notebook.
Record your thinking — optional4 prompts
Use these prompts if they help students capture evidence, decisions, or questions. You do not need to complete every prompt or create an entry at every step.
Nothing is saved until you choose this button.
Troubleshooting
One press advances several states
Act only on the transition and add a short debounce interval if the physical contact produces repeated edges.
The system becomes stuck
Trace every state's allowed transitions and make sure at least one defined path returns to READY.
2026 middle school standards
Potential CSTA connections
These are evidence-based crosswalk candidates for curriculum review—not a claim of official alignment.
Analyze the roles of iteration, selection, variables, and procedures in a segment of code.
Students trace variables, selection, or iteration in the supplied sketch and connect code to physical behavior.
Lesson evidence: State transition traceUse systematic strategies to test, refine, and document changes to a computing technology to meet the intended purpose.
Students isolate variables, compare observed behavior with the intended purpose, and document a revision.
Lesson evidence: Event-sequence test tableSupporting concepts
floating-inputs · sketch-foundations
Sources and review
Arduino Uno R3 documentationArduino Projects Book · CC BY-NC-SA 3.0Starting point, not verified curriculum. Review the actual hardware, circuit, code, power requirements, and classroom conditions.
After teaching this lesson