Switching Loads with Arduino and Solid State Relays

What is a Solid State Relay?

A Solid State Relay (SSR) is a semiconductor-based device that behaves like a traditional relay but lacks moving parts, making it faster, more durable, and silent. It is ideal for controlling high-voltage loads with Arduino.

How Does a Solid State Relay Work?

An SSR uses a triac to control AC loads. The triac conducts electricity in both positive and negative AC cycles and deactivates at zero crossing. Optocouplers ensure isolation between the high-power and control circuits.

Connection Diagram

Connect the load to the SSR terminals and the control pins (DC+ and DC-) to Arduino's 5V and GND. The signal pin (CH1) is connected to a digital output on Arduino to switch the relay on or off.

Example Code

The following example toggles the SSR every 10 seconds, turning the connected load on and off.

// Example: Controlling an SSR with Arduino
const int pin = 9;

void setup()
{
    Serial.begin(9600);    // Start Serial communication
    pinMode(pin, OUTPUT);  // Set pin as OUTPUT
}

void loop()
{
    digitalWrite(pin, HIGH);   // Turn SSR ON
    delay(10000);              // Wait 10 seconds
    digitalWrite(pin, LOW);    // Turn SSR OFF
    delay(10000);              // Wait 10 seconds
}