Lesson 5: Servo & Knob

Turn the knob and the servo arm follows it. Leave the knob alone for 4 seconds and the servo starts sweeping by itself.

One of 7 projects in the Arduino UNO Sensor & Output Starter Kit - LEDs, Buzzer, Servo, Ultras… — the parts below are from that kit.

Before you start

What you build and learn

• How a servo holds an angle
• Using map() to turn 0-1023 into 10-170 degrees
• Using a library (Servo.h)
• Switching between knob mode and automatic mode with millis()

New words

Servo

A small motor with gears and a position sensor inside. You tell it an angle and it moves there and holds it.

Library

Ready-made code you include, like #include <Servo.h>. The Servo library comes with the Arduino IDE.

millis()

The number of milliseconds since the UNO started. Used here to tell how long the knob has been still.

What this project uses

Every item is in the kit — nothing extra to buy.

UNO R3 UNO R3 Development Board ATmega328P Microcontroller with USB Cable, 5V Logic, 14 Digital I/O, 6 Analog Inputs… UNOR3

In the kit

SG90 servo SG90 9g Micro Servo Motor, 180° Position Control PWM RC Servo, 4.8V–6V Mini Servomotor for Arduino ESP32 RC M… SG90

In the kit

10K potentiometer 10K Ohm Rotary Potentiometer PCB Type - 3-Pin Variable Resistor for Arduino Analog Input & DIY Electronics DIY-220

In the kit

breadboard 400 Tie Point Solderless Breadboard - Half Size Prototyping Circuit Board with Power Rails, for Arduino & Ele… DIY-238

In the kit

jumper wires Jumper Wire Assorted Pack 120 Pieces - Male-to-Male, Male-to-Female, Female-to-Female 10cm Ribbon Cables for… DIY-212

In the kit

Basics HC-SR04 Ultrasonic Distance Sensor Module for Arduino, Raspberry Pi & DIY Robotics Projects, 5V Trigger/Echo… DIY-00043

In the kit

Build this with

Arduino UNO Sensor & Output Starter Kit - LEDs, Buzzer, Servo, Ultrasonic & LCD

All 10 parts in one box, with this project and 6 more to build from them.

AED 85.00 See the kit Add kit to cart

Need only these parts? Order them loose · from AED 102.23 ▾

Used in this project tick what you still need

UNO R3 UNO R3 Development Board ATmega328P Microcontroller with USB Cable, 5V Logic, 14 Digital I/O, 6 Analog Inputs… UNOR3 · ×1

AED 26.39

In stock

SG90 servo SG90 9g Micro Servo Motor, 180° Position Control PWM RC Servo, 4.8V–6V Mini Servomotor for Arduino ESP32 RC M… SG90 · ×1

AED 13.67

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10K potentiometer 10K Ohm Rotary Potentiometer PCB Type - 3-Pin Variable Resistor for Arduino Analog Input & DIY Electronics DIY-220 · ×1

AED 10.26

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breadboard 400 Tie Point Solderless Breadboard - Half Size Prototyping Circuit Board with Power Rails, for Arduino & Ele… DIY-238 · ×1

AED 11.58

In stock

jumper wires Jumper Wire Assorted Pack 120 Pieces - Male-to-Male, Male-to-Female, Female-to-Female 10cm Ribbon Cables for… DIY-212 · ×1

AED 25.02

In stock

Also needed untick if you already have them

Basics HC-SR04 Ultrasonic Distance Sensor Module for Arduino, Raspberry Pi & DIY Robotics Projects, 5V Trigger/Echo… DIY-00043 · ×1

AED 15.31

In stock

Selected parts AED 102.23

Add 6 parts to cart

One of each part. Packs (resistor assortment, jumper wires) already hold more than a single build needs. Delivery is AED 20, free on orders AED 100+.

Connections

Unplug USB before you change any wire. Pin names are the labels printed on the board.

Step by step

One thing at a time. Tick nothing off until it matches the diagram.

1. Unplug the USB cable.Watch out: Always unplug the USB cable before you add, move or remove a wire.
2. Press one small plastic arm onto the servo's shaft so you can see it move.Watch out: Don't fix anything else to the arm, and don't twist it by hand: that can strip the servo's plastic gears.
3. Push three male-to-male jumper wires into the servo's plug. Connect orange to UNO pin 5, red to the + rail and brown to the − rail.
4. Check the potentiometer's middle pin is still on A0.
5. Plug in USB and upload the Lesson 5 code.Watch out: If the UNO's lights flicker, it keeps restarting or the servo twitches, unplug USB straight away and read "If it doesn't work".
6. Turn the knob slowly. Then let go and wait 4 seconds.

Sketch for this project

Written for the board in the kit. Copy it into the Arduino IDE; change the pin numbers if you wire it differently.

/*
  DIY KIT - Arduino UNO Sensor & Output Starter Kit
  Lesson 5 of 7: Servo & Knob

  WIRING (unplug the USB cable before you wire)
    SG90 servo, using 3 male-to-male jumper wires in its plug:
      orange (signal) -> UNO pin 5
      red (+)         -> 5V
      brown (-)       -> GND
    Potentiometer (still wired from Lesson 1):
      outer pins -> 5V and GND, middle pin -> UNO pin A0
    Parts from Lessons 1-4 can stay where they are.

  POWER: fit only the small plastic arm - nothing else on the servo.
  If the UNO resets or the servo twitches, unplug USB and read the
  troubleshooting table on the lesson page.

  WHAT SHOULD HAPPEN
    Turn the knob: the arm follows it. Let go for 4 seconds: the arm
    sweeps back and forth by itself until you turn the knob again.
*/

#include <Servo.h>   // comes with the Arduino IDE - nothing to install

const int SERVO_PIN = 5;
const int KNOB_PIN  = A0;

const int MIN_ANGLE = 10;    // the servo's travel limits, in degrees
const int MAX_ANGLE = 170;   // (0 and 180 can make some servos buzz at the end)
const int SWEEP_STEP = 2;                      // degrees per step while sweeping
const unsigned long SWEEP_STEP_MS = 20;        // smaller = faster sweep
const unsigned long WAIT_BEFORE_SWEEP_MS = 4000;
const int KNOB_DEADBAND = 8;                   // ignore tiny wobbles of the knob

Servo servo;
int lastKnob = -1000;
unsigned long lastKnobMove = 0;
int sweepAngle = 90;
int sweepDirection = 1;        // +1 = counting up, -1 = counting down
unsigned long lastSweepStep = 0;

void setup() {
  servo.attach(SERVO_PIN);     // the Servo library now pulses pin 5 for us
  servo.write(90);             // start in the middle
  Serial.begin(9600);
  Serial.println("Lesson 5: Servo & Knob - turn the knob, or wait for the sweep");
}

void loop() {
  int knob = analogRead(KNOB_PIN);   // 0 ... 1023

  if (abs(knob - lastKnob) > KNOB_DEADBAND) {
    // The knob moved: the arm follows it.
    lastKnob = knob;
    lastKnobMove = millis();
    int angle = map(knob, 0, 1023, MIN_ANGLE, MAX_ANGLE);
    servo.write(angle);
    sweepAngle = angle;
    Serial.print("knob ");
    Serial.print(knob);
    Serial.print(" -> ");
    Serial.print(angle);
    Serial.println(" degrees");
  } else if (millis() - lastKnobMove > WAIT_BEFORE_SWEEP_MS && millis() - lastSweepStep > SWEEP_STEP_MS) {
    // Nobody touched the knob for 4 seconds: sweep by ourselves.
    lastSweepStep = millis();
    sweepAngle = sweepAngle + sweepDirection * SWEEP_STEP;
    if (sweepAngle >= MAX_ANGLE) { sweepAngle = MAX_ANGLE; sweepDirection = -1; }
    if (sweepAngle <= MIN_ANGLE) { sweepAngle = MIN_ANGLE; sweepDirection = 1; }
    servo.write(sweepAngle);
  }

  delay(10);
}

Upload it

1. Click Copy (or Download .ino and open the file).
2. In the Arduino IDE choose File → New Sketch, select everything in it and paste.
3. Check the bottom of the window says Arduino Uno and your port (Start here, step 5).
4. Click Upload (the → arrow) and wait for Done uploading.

How the code works

Change it and see

What you should see or hear

• The arm follows the knob from one end of its travel to the other.
• The Serial Monitor prints lines like: knob 512 -> 90 degrees.
• After 4 seconds without touching the knob, the arm sweeps back and forth until you turn the knob again.

If it doesn't work

Small experiment

Stick a small paper pointer on the arm and draw a scale behind it (10°, 90°, 170°). When the Serial Monitor says 90 degrees, does the pointer really point to the middle?

Check what you learned

Next

• Lesson 6 adds the LCD. The potentiometer moves to become the LCD's contrast knob.

Hi DIY KIT, I'm stuck on the Arduino UNO Sensor & Output Starter Kit.
Lesson: __
Step number: __
What should happen: __
What happens instead: __
Error message (copied exactly): __
I'll attach a photo of my wiring.

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