Arduino Uno R3

Trigger to servo motion

Use a verified digital trigger to command two bounded servo positions and test the motion safely.

CSTA 2026 mapping candidatesNot reviewed by CSTA

MS-PRO-RD-17ProgrammingMS-PRO-TR-19Programming

Students will

Attach and command a servo with the Servo library
Constrain motion to reviewed positions
Separate a control signal from actuator power requirements

Evidence of success

Servo reaches both positions without binding
Released and pressed states consistently select the intended position
Student explains why the signal pin does not supply motor power

Hardware

Arduino Uno R3
Starter Kit hobby servo
Momentary pushbutton
Breadboard and jumper wires

Prerequisites

Read a reliable digital input
Identify servo power, ground, and signal leads

Before class

Verify the actual servo lead order
Test one servo with the intended supply before class
Set a safe mechanical range and keep hands clear of attached mechanisms

Reviewed connection map

Button-triggered servo

Button D8-GNDINPUT_PULLUP trigger

Servo signal D9Position command

Servo power + GNDReviewed supply and shared ground

Servo mechanismMove only within verified safe angles

Connect the button between D8 and GND.
Connect the servo signal to D9 and its verified power and ground leads to the reviewed supply.
Test unloaded positions before attaching a mechanism.

Build and test

01Connect servo GND, 5V, and signal to the verified pins
02Upload a two-position test with no mechanism attached
03Wire the D8 button using INPUT_PULLUP
04Command the active position only when the trigger is verified
05Attach the mechanism and reduce the range if it binds

Read before uploading

Annotated Arduino sketch

#include <Servo.h>

const int BUTTON_PIN = 8;
const int SERVO_PIN = 9;
Servo actuator;

void setup() {
  pinMode(BUTTON_PIN, INPUT_PULLUP);
  actuator.attach(SERVO_PIN);
  actuator.write(20);
}

void loop() {
  bool triggered = digitalRead(BUTTON_PIN) == LOW;
  actuator.write(triggered ? 100 : 20);
  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.

Predict: Before you begin, what do you expect to observe when you attach and command a servo with the Servo library?Evidence: What evidence best demonstrates this result: Servo reaches both positions without binding?Debug: If you encounter “Uno resets when the servo starts,” what will you check first, and why?Transfer: Where could you reuse the skill from “Trigger to servo motion” in another classroom project?

Nothing is saved until you choose this button.

Troubleshooting

Uno resets when the servo starts

Remove the mechanism, inspect the supply, and use an appropriate external servo supply with common ground if required.

Servo moves unpredictably

Verify lead order, common ground, signal pin, and commanded angle bounds.

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-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: Trigger, angle variable, and motion trace

MS-PRO-TR-19

Use 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: Range and repeated-trigger test

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

Supporting concepts

power-and-signals · component-boards · motor-types

Sources and review

Arduino Uno R3 documentation Arduino Projects Book · CC BY-NC-SA 3.0 Arduino Servo library

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

After teaching this lesson