PROJECT 7 · WI‑FI / WEB

Relay Web Server

Switch a relay from a web page — a tiny 3.3 V signal controlling a much larger circuit.

⬇ Download the sketch Save Project_7_ESP32_Relay_Web_Server.ino, then open it in the Arduino IDE (setup: Project 0b). Needs the ESPAsyncWebServer + AsyncTCP libraries and your Wi‑Fi credentials.

⚠️ Safety first. Mains voltage (120 V / 230 V) is dangerous. In this project use only low‑voltage loads (the kit's LED). Never wire mains while powered; if you're not experienced with mains, don't use it — ask someone who is.

1 · What a relay is

A relay is an electrically‑operated switch. A small coil current (from an ESP32 GPIO) flips a mechanical contact, connecting or disconnecting a separate higher‑power circuit — the two sides electrically isolated.

2-channel relay module labeled — Switched terminals + control pins.

Relay module screw terminals — The screw terminals (COM/NO/NC).

Switched side — COM / NO / NC

COM — the wire you're switching.
NO (Normally Open) — off until triggered → use for off by default.
NC (Normally Closed) — on until triggered → use for on by default.

Control side — VCC / GND / IN

Relay control pins VCC GND IN1 IN2 — VCC/GND power it; IN1/IN2 are the ESP32 triggers.

JD-VCC jumper on the relay module — JD‑VCC jumper — leave on for the simplest wiring.

2 · Install the required libraries

This project uses the asynchronous server libraries — install both:

ESPAsyncWebServer
AsyncTCP (ESP32)

Add each via Sketch → Include Library → Add .ZIP Library…, then restart the IDE.

3 · Wiring

Relay wired to the ESP32 with an LED as the safe load — Relay VCC→VIN, GND→GND, IN1→GPIO 26; LED switched through COM→NO.

Relay VCC → VIN (5 V) · GND → GND
Relay IN1 → GPIO 26 (IN2 → GPIO 27 for channel 2)
Switched side: LED (with 220 Ω) through COM → NO

4 · Upload & use

Set your Wi‑Fi credentials, upload, open Serial Monitor at 115200, press EN/RESET:

==============================================
 Project 7: ESP32 Relay Web Server
==============================================
2 relay(s), mode: Normally Open (NO)
Relay #1 -> GPIO 26
Relay #2 -> GPIO 27
Connecting to Wi-Fi: MyNetwork
....
Wi-Fi connected!
Open this address in your browser:  http://192.168.1.42
----------------------------------------------
[WEB] Relay #1 -> ON

Open the address; flip a toggle → the relay clicks and the clean line above prints (the original sketch printed a cryptic NO 11).

NO‑mode note: in Normally‑Open mode the relay is off when the pin is HIGH, so the sketch writes the inverse of the requested state. That's expected.

5 · Demonstration

Relay module and web toggles controlling an LED — Toggle from your phone; the relay clicks and the load follows.

6 · Troubleshooting

Symptom	Likely cause	Fix
Compile error on `ESPAsyncWebServer`	Libraries missing	Install ESPAsyncWebServer and AsyncTCP
Relay clicks, load doesn't switch	Wired to NC	Use COM → NO
Toggle seems inverted	NO‑mode inversion (normal)	Leave the sketch as‑is
No click at all	IN mis‑wired / module unpowered	IN → GPIO 26/27; VCC→VIN, GND→GND
Stuck on "Connecting…"	Wrong credentials / 5 GHz	Fix credentials; use 2.4 GHz