How to Connect an SSR Relay to an Arduino (Step-by-Step Guide)

To connect an SSR-40DA (Solid State Relay) to an Arduino, follow this safe and simple wiring and setup guide. The SSR-40DA is designed to control AC loads using a DC signal from the Arduino.

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⚠️ IMPORTANT SAFETY NOTE:

The AC side of the SSR handles high voltage (110V or 220V AC). Take extreme caution and disconnect power before wiring. If unsure, consult a qualified electrician.

🧰 What You Need:

🧠 SSR-40DA Pin Layout:

Input Side (DC, from Arduino):
- + (positive) — Connects to 220R and Arduino digital pin (e.g., D8)
- – (negative) — Connects to Arduino GND
Output Side (AC load):
- 1 / Load In — AC live (L) wire from source
- 2 / Load Out — AC live (L) wire to the appliance
  (AC neutral (N) wire goes directly to the appliance and power source)

🧯 Wiring Diagram:

✅ Arduino Example Code:

int relayPin = 8;

void setup() {
  pinMode(relayPin, OUTPUT);
}

void loop() {
  digitalWrite(relayPin, HIGH); // Turns ON the AC load
  delay(5000);                  // Wait 5 seconds
  digitalWrite(relayPin, LOW);  // Turns OFF the AC load
  delay(5000);                  // Wait 5 seconds
}

🧊 Notes:

The SSR-40DA triggers with 3–32V DC, so a 5V signal from Arduino is safe.
When activated, the SSR closes the circuit and lets AC flow to the load.
A heatsink is highly recommended if you control loads above ~10A.
SSRs do not click like mechanical relays — they switch silently.

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