Isolated Inputs and Outputs with Arduino and Optocoupler

What is an Optocoupler?

An optocoupler uses light to connect two circuits while maintaining galvanic isolation. It protects control electronics from overvoltage, noise, and spikes.

How Does an Optocoupler Work?

Optocouplers consist of an IR LED and a photoreceptor (transistor, photodiode, or phototriac) inside a single package. Light transmits the signal across circuits.

Using Optocouplers with Arduino

Optocouplers can isolate Arduino signals when emitting or receiving. Below are two common configurations.

1. Arduino Emitting a Signal

Connect the primary circuit (LED side) to Arduino, adding a current-limiting resistor. The secondary side behaves like a switch for the load.

2. Arduino Receiving a Signal

Use the secondary side to trigger Arduino as if it were reading a button input.

Example Code

// Example: Reading an optocoupler signal with Arduino
const int optoPin = 2;

void setup() {
    pinMode(optoPin, INPUT_PULLUP);
    Serial.begin(9600);
}

void loop() {
    int state = digitalRead(optoPin);
    if (state == LOW) {
        Serial.println("Signal received!");
    }
    delay(100);
}