ESP8266 5V WiFi Relay Board (ESP-01S) – User’s Guide
Overview
This module combines an ESP-01S WiFi microcontroller with a 5V relay, enabling remote switching of AC/DC loads via WiFi. Ideal for IoT, smart home, and automation projects.
- Relay Rating: 10A @ 250VAC / 30VDC
- Control Pin: GPIO0 (active LOW)
- Power Supply: 5V DC (≥250mA)
- Communication: WiFi (802.11 b/g/n)
What You’ll Need
- ESP-01S WiFi Module
- ESP-01 Relay Board
- USB-to-Serial (FTDI) adapter
- Jumper wires
- 5V DC power supply
- Arduino IDE (or other ESP8266-compatible IDE)
Hardware Setup
Pin Mapping (ESP-01S)
| Pin | Function |
|---|---|
| VCC | 3.3V power input |
| GND | Ground |
| RX | Serial receive |
| TX | Serial transmit |
| GPIO0 | Relay control (LOW = ON) |
| GPIO2 | General I/O |
| CH_PD | Chip enable (tie to VCC) |
| RST | Reset (optional) |
Important: ESP-01S logic is 3.3V. Do not connect RX/TX directly to 5V UART without level shifting.
Wiring for Programming
Connect ESP-01S to FTDI adapter:
- RX ↔ TX
- TX ↔ RX
- VCC ↔ 3.3V
- GND ↔ GND
- CH_PD ↔ 3.3V
- GPIO0 ↔ GND (for flashing mode)
Once programmed, plug ESP-01S into the relay board.
Software Setup
1. Install ESP8266 Board in Arduino IDE
- Go to File > Preferences
- Add board URL:
http://arduino.esp8266.com/stable/package_esp8266com_index.json - Install via Boards Manager
2. Sample Code
#include <ESP8266WiFi.h>
const char* ssid = "YOUR_SSID";
const char* password = "YOUR_PASSWORD";
WiFiServer server(80);
int relayPin = 0; // GPIO0
void setup() {
pinMode(relayPin, OUTPUT);
digitalWrite(relayPin, HIGH); // Relay OFF
Serial.begin(115200);
WiFi.begin(ssid, password);
while (WiFi.status() != WL_CONNECTED) delay(500);
server.begin();
}
void loop() {
WiFiClient client = server.available();
if (client) {
String req = client.readStringUntil('\r');
client.flush();
if (req.indexOf("/ON") != -1) digitalWrite(relayPin, LOW);
if (req.indexOf("/OFF") != -1) digitalWrite(relayPin, HIGH);
client.print("Relay is now ");
client.print(digitalRead(relayPin) == LOW ? "ON" : "OFF");
}
}Access via browser: http://<ESP_IP>/ON or /OFF
Troubleshooting Tips
| Issue | Solution |
|---|---|
| ESP-01S not responding | Check 3.3V supply and CH_PD connection |
| Relay not switching | Ensure GPIO0 is driven LOW to activate |
| Programming fails | Confirm GPIO0 is grounded during upload |
| WiFi not connecting | Double-check SSID/password and signal strength |
Pro Tips for Integration
- Use optocoupler isolation if switching high-voltage loads
- Add flyback diode across relay coil for protection
- Consider MQTT or Blynk for scalable IoT control
- Use deep sleep for battery-powered applications (requires GPIO16–RST bridge)