ESP-01 SSR AC Relay Module, AC 4A-600V — for Smart Home and DIY Projects

Discontinued RobotDyn SKU: RD-ESP01-SSR-RELAY
ESP-01 SSR AC Relay Module, AC 4A-600V — for Smart Home and DIY Projects

Overview

The RobotDyn ESP-01 SSR Relay is a solid-state AC relay with an integrated ESP-01 (ESP8266) socket. It switches AC loads up to 4 A at 600 V using a BT136-600B TRIAC triggered through a MOC3042 zero-crossing optoisolator — no mechanical contacts, no clicking sound, no contact wear.

The ESP-01 socket lets you drop in any ESP-01 (or ESP-01S) module and gain WiFi control with a few lines of code, turning the relay into a smart-switch suitable for home automation, Tasmota/ESPHome/MQTT integration, or custom WiFi-connected devices.

Why Solid State vs. Mechanical Relay?

FeatureMechanical RelayThis SSR
Lifetime~100,000 cycles>10 million cycles
Switching speed5–15 ms<20 ms
Audible noise”Click”Silent
Vibration sensitivityYesNo
Inrush handlingGood for resistiveBetter with snubber
CostLowerSlightly higher
EMILowerTRIAC generates RF noise

Solid-state relays are ideal for frequent switching (PWM-style heating control, motor speed via burst-firing) and silent operation (bedroom lamps, baby room controllers).

ESP-01 Pinout (when installed)

The relay is triggered by the ESP-01’s GPIO0 going HIGH. Available GPIOs after installation:

ESP-01 PinFunction
GPIO0TRIAC trigger (HIGH = relay on)
GPIO2Free for use (e.g., onboard LED control, external sensor)
TX/RXUART (also act as GPIO1/GPIO3)

External switch (dry contact) terminals are also exposed — wire a wall switch in parallel for hybrid local + WiFi control.

Sample Code (Arduino ESP8266 Core)

#include <ESP8266WiFi.h>

const char* ssid = "YourWiFi";
const char* password = "YourPassword";
const int relayPin = 0;   // GPIO0

WiFiServer server(80);

void setup() {
  pinMode(relayPin, OUTPUT);
  digitalWrite(relayPin, LOW);   // relay off

  WiFi.begin(ssid, password);
  while (WiFi.status() != WL_CONNECTED) delay(500);
  server.begin();
}

void loop() {
  WiFiClient client = server.available();
  if (!client) return;
  String req = client.readStringUntil('\r');
  if (req.indexOf("/on") != -1)  digitalWrite(relayPin, HIGH);
  if (req.indexOf("/off") != -1) digitalWrite(relayPin, LOW);
  client.print("HTTP/1.1 200 OK\r\n\r\nOK");
  client.stop();
}

For a more polished setup, flash Tasmota or ESPHome onto the ESP-01 — both provide rich UIs, MQTT integration, and Home Assistant support out of the box.

Safety Notes

This relay switches mains voltage. Required precautions:

Common Uses

Where to Buy in 2026

Look for boards explicitly with the MOC3042 optoisolator (zero-cross switching reduces EMI) and BT136-600B TRIAC. Some cheaper clones use non-zero-cross optoisolators which generate more noise.

Documentation