Arduino Uno R3

Sequence without blocking

Coordinate timed outputs while the sketch continues checking inputs, using elapsed time instead of long delays.

CSTA 2026 mapping candidatesNot reviewed by CSTA

MS-PRO-PD-12ProgrammingMS-PRO-RD-17Programming

Students will

Explain how delay prevents other observations
Use millis to schedule repeated behavior
Keep an input responsive during an output sequence

Evidence of success

The LED follows its interval without delay
Button presses are observed while the timed behavior continues
The student can identify the stored timestamp, interval, and elapsed-time comparison

Hardware

Arduino Uno R3
Built-in LED or protected external LED
Momentary pushbutton
Breadboard and jumper wires if using external parts

Prerequisites

Read a reliable digital input
Control a digital output
Use variables and conditions

Before class

Prepare a delay-based comparison sketch
Use unsigned long for elapsed-time values
Choose intervals that learners can observe

Reviewed connection map

Timed output with responsive input

Button D8-GNDStable active-low input

Arduino loopChecks elapsed time and input every pass

LED_BUILTINTimed visible output

Serial MonitorImmediate button evidence over USB

Connect the button between D8 and GND.
The timed output uses the built-in LED, so no external output circuit is required.

Build and test

01Run a blinking sketch that uses delay and try to read a button during the wait
02Record why responsiveness is limited
03Store the last-change time and compare it with millis
04Toggle the LED only when the interval has elapsed
05Add button reporting and verify it remains responsive between LED changes

Read before uploading

Annotated Arduino sketch

const int BUTTON_PIN = 8;
const unsigned long INTERVAL = 500;
unsigned long lastChange = 0;
bool ledState = LOW;

void setup() {
  pinMode(LED_BUILTIN, OUTPUT);
  pinMode(BUTTON_PIN, INPUT_PULLUP);
  Serial.begin(9600);
}

void loop() {
  unsigned long now = millis();
  if (now - lastChange >= INTERVAL) {
    lastChange = now;
    ledState = !ledState;
    digitalWrite(LED_BUILTIN, ledState);
  }
  if (digitalRead(BUTTON_PIN) == LOW) Serial.println("pressed");
}

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.

Predict: Before you begin, what do you expect to observe when you explain how delay prevents other observations?Evidence: What evidence best demonstrates this result: The LED follows its interval without delay?Debug: If you encounter “The output changes continuously,” what will you check first, and why?Transfer: Where could you reuse the skill from “Sequence without blocking” in another classroom project?

Nothing is saved until you choose this button.

Troubleshooting

The output changes continuously

Update the saved timestamp only when the scheduled action occurs.

Timing fails after code changes

Keep millis-related variables unsigned long and compare elapsed time by subtraction.

2026 middle school standards

Potential CSTA connections

Not reviewed by CSTA

These are evidence-based crosswalk candidates for curriculum review—not a claim of official alignment.

MS-PRO-PD-12

Use a procedure to structure code for clarity and reusability.

Students use a named procedure to separate repeated output behavior from timing logic.

Lesson evidence: Annotated reusable procedure

MS-PRO-RD-17

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: millis, comparison, and loop trace

View the official 2026 CSTA standardsStandard text: Computer Science Teachers Association (2026), CC BY-NC-SA 4.0.

Supporting concepts

sketch-foundations

Sources and review

Arduino Uno R3 documentation Arduino Projects Book · CC BY-NC-SA 3.0 Arduino Blink Without Delay example

Starting point, not verified curriculum. Review the actual hardware, circuit, code, power requirements, and classroom conditions.

After teaching this lesson