Pneumatics and other actuators

Learn

What you’ll learn

• How pneumatics move things with compressed air
• How to drive solenoids safely
• How to use buzzers and lights as outputs

Pneumatics

A pneumatic cylinder pushes a piston out when compressed air enters. You need an air supply (a compressor or a tank, or a hand pump), tubing, and a solenoid valve that an electrical signal opens and closes. Pneumatics are fast and powerful, and good for punching, lifting and soft grippers. FIRST and VEX robots often use them.

Solenoids

A solenoid is a coil with a metal plunger: power on, the plunger pulls in. It’s used for locks, valves and “kickers”.

• Needs much more current than a pin can give: switch it with a transistor or MOSFET.
• Add a flyback diode across the coil. When the coil switches off it produces a voltage spike that can destroy the transistor, and the diode safely absorbs it. The same applies to relays and motors.

Buzzers

Type	How to use
Active buzzer	Beeps at one pitch when given power: digitalWrite(pin, HIGH)
Passive buzzer (or small speaker)	Plays any pitch with tone(pin, frequency)

Lights

• Single LEDs with resistors (see your first circuit).
• Addressable RGB LEDs (WS2812, “NeoPixels”): a whole strip controlled from one pin, any colour per LED, using the Adafruit NeoPixel or FastLED library.

Examples

Example: a solenoid circuit

 Arduino pin ── 1 kΩ ── transistor base
 +12 V ── solenoid ── transistor collector,  transistor emitter ── GND
 flyback diode across the solenoid (stripe towards +12 V)
 Arduino GND joined to the 12 V supply's GND

Example: robot sounds

void beepStartup() {
  tone(8, 880, 100); delay(150);
  tone(8, 1320, 150);
}
void beepObstacle() { tone(8, 440, 60); }

Sounds make debugging easier: the robot can “say” which state it’s in without a computer attached.

Practice

Try it in the virtual Arduino

Press Start simulator, open the diagram.json tab and replace its contents with the wiring below, then paste the sketch into sketch.ino and press the green ▶.

diagram.json

{
  "version": 1,
  "author": "RoboLearn",
  "editor": "wokwi",
  "parts": [
    {
      "type": "wokwi-arduino-uno",
      "id": "uno",
      "top": 0,
      "left": 0,
      "attrs": {}
    },
    {
      "type": "wokwi-buzzer",
      "id": "bz1",
      "top": -90,
      "left": 150,
      "attrs": {
        "volume": "0.1"
      }
    }
  ],
  "connections": [
    [
      "bz1:1",
      "uno:GND.1",
      "black",
      []
    ],
    [
      "bz1:2",
      "uno:8",
      "red",
      []
    ]
  ],
  "dependencies": {}
}

sketch.ino

const int BUZZER = 8;
int notes[] = {262, 294, 330, 349, 392, 440, 494, 523};   // C D E F G A B C

void setup() {
  for (int i = 0; i < 8; i++) {
    tone(BUZZER, notes[i], 200);
    delay(250);
  }
}

void loop() {}

Buzzer tunes with tone()Open full screen ↗

Start simulator

Runs on Wokwi, free, no account needed.

Reverse the scaleEasy

Play the scale from high to low. Loop backwards: for (int i = 7; i >= 0; i--).

SirenMedium

Make a siren that sweeps the pitch up from 400 Hz to 1,200 Hz and back, forever.

Show an answer

void loop() {
  for (int f = 400; f <= 1200; f += 10) { tone(8, f); delay(5); }
  for (int f = 1200; f >= 400; f -= 10) { tone(8, f); delay(5); }
}

Why the diode?Hard

Explain in your own words why a flyback diode is needed across a solenoid or relay coil. When the current through a coil is suddenly switched off, its magnetic field collapses and creates a high voltage spike. The diode gives that energy a safe loop to flow round, instead of it breaking down the transistor.

Quick check

1. What switches air on and off in a pneumatic system?

A potentiometerA solenoid valveAn LEDA gear

2. Why add a flyback diode across a solenoid?

To make it strongerTo protect the transistor from the switch-off voltage spikeTo light it upTo measure current

3. Which buzzer can play tunes with tone()?

Active buzzerPassive buzzerNeitherBoth, only at one pitch

Check my answers