Documentation

Overview

This 1-channel module puts a single Omron G3MB-202P solid state relay on a compact board, letting a microcontroller switch one AC load — a lamp, fan, pump, or heater up to 2 A at 24–240 V AC — in total silence. There is no coil and no moving contact: your logic signal drives an LED inside the SSR, and an opto-triac on the AC side conducts. Switching happens at the AC zero-crossing, so it is electrically quiet and gentle on loads.

The trigger logic on this board is active LOW: pull the CH input to ground and the relay conducts; release it (or drive it HIGH) and the load switches off at the next zero-crossing. The DC side takes 5 V on DC+ and ground on DC−, with the on-board LED mirroring the channel state. The AC load wires into the 2-position output terminal in series with the live conductor.

Because the output is a triac, two rules are absolute: AC loads only (DC latches the triac on), and 2 A maximum. Respect those and this is the cleanest way to give one mains device a brain. This manual covers the pinout, wiring for Arduino, ESP32, Raspberry Pi, and Pico, active-low code for each, and the SSR behaviors worth knowing before the first switch-on.

At a Glance

Specifications

Pinout Diagram

Top terminal, left to right: CH (trigger, active low), DC− (ground), DC+ (5 V). Bottom terminal: the switched AC path — wire it in series with the load’s live conductor, with neutral running to the load directly.

Wiring Guide

Code Examples

Arduino — Active-Low Relay Control

const int CH = 7;

void setup() {
  digitalWrite(CH, HIGH);   // define OFF state before...
  pinMode(CH, OUTPUT);      // ...the pin becomes an output
}

void loop() {
  digitalWrite(CH, LOW);    // load ON
  delay(3000);
  digitalWrite(CH, HIGH);   // load OFF
  delay(3000);
}

ESP32 — Serial-Controlled Switch

const int CH = 26;

void setup() {
  Serial.begin(115200);
  digitalWrite(CH, HIGH);
  pinMode(CH, OUTPUT);
  Serial.println("Send 1 = ON, 0 = OFF");
}

void loop() {
  if (Serial.available()) {
    char c = Serial.read();
    if (c == '1') { digitalWrite(CH, LOW);  Serial.println("ON");  }
    if (c == '0') { digitalWrite(CH, HIGH); Serial.println("OFF"); }
  }
}

Raspberry Pi — Python (gpiozero)

from gpiozero import DigitalOutputDevice
from time import sleep

# active_high=False: on() pulls CH low, which turns the SSR on
relay = DigitalOutputDevice(17, active_high=False, initial_value=False)

try:
    while True:
        relay.on()
        print("Load ON")
        sleep(5)
        relay.off()
        print("Load OFF")
        sleep(5)
except KeyboardInterrupt:
    relay.off()

Raspberry Pi Pico — MicroPython

from machine import Pin
import time

ch = Pin(16, Pin.OUT, value=1)   # start HIGH = OFF

def load_on():
    ch.value(0)     # active low

def load_off():
    ch.value(1)

while True:
    load_on()
    time.sleep(4)
    load_off()
    time.sleep(4)

Frequently Asked Questions

Related Tutorials