1
1. Prepare Arduino IDE and Libraries
Install the Arduino IDE if you haven't already. Add ESP32 board support via the Boards Manager (search for 'esp32'). Install the Blynk library from the Library Manager (search for 'Blynk').
IoT & Wireless
ESP32 Blynk IoT Smart Relay Switch
A Wi-Fi-enabled home automation switch using the ESP32 DevKit V1 and Blynk IoT cloud to safely control high-voltage AC appliances from a mobile device.
Safety first, read before building.
Safety notice
This project involves potentially lethal mains voltage. The ESP32 is a low-voltage device, and its GPIO must never be connected directly to 220V AC. Use a correctly rated relay, suitable isolation, a secure enclosure and appropriate electrical protection. Mains-side assembly and verification must be handled by a qualified electrician.
What you will build and learn
Interface an ESP32 microcontroller with the Blynk IoT cloud platform via Wi-Fi
Implement bidirectional communication using Blynk Virtual Pins and event handlers
Safely drive an optoisolated electromechanical relay module from 3.3V logic
Identify and prevent floating state and boot-glitch issues on ESP32 output GPIOs
Prerequisites
Arduino IDE configured with the ESP32 board package and Blynk library, Registered Blynk.Cloud developer account and mobile application, Basic understanding of AC mains electrical safety, fusing, and isolation
System Overview
This project implements an IoT power-switching node using an ESP32 DevKit V1 connected to the Blynk 2.0 Cloud platform. It enables real-time remote switching of AC mains loads (such as an LED bulb) via a smartphone interface.
Architecture & Operating Principle
The signal and power chain functions as follows:
[Blynk Mobile App]
│ (HTTPS/WebSockets)
▼
[Blynk Cloud Platform]
│ (Wi-Fi 802.11 b/g/n @ 2.4 GHz)
▼
[ESP32 DevKit V1]
│ (3.3V / 5V Logic GPIO)
▼
[Optoisolated Relay Module]
│ (Mechanical Dry Contacts: COM & NO)
▼
[220V AC Mains Load (Bulb)]
- Virtual Pin Mapping: The Blynk dashboard uses Virtual Pin
V0configured as an integer datastream (0 or 1). Actuating the mobile switch triggers an event pushed by Blynk Cloud to the ESP32. - Firmware Handling: The ESP32 firmware intercepts state transitions using the
BLYNK_WRITE(V0)macro. The incoming parameter integer (param.asInt()) is evaluated to drive the target output GPIO. - Relay Isolation & Control: The GPIO drives an optocoupler on the relay module. When energized, the relay coil pulls the Normally Open (NO) contact to Common (COM), closing the live conductor of the 220V AC circuit.
Hardware Considerations & Mains Safety
- Galvanic Isolation: The relay's optoisolator prevents high-voltage inductive spikes or ground faults from backfeeding into the ESP32.
- Boot State Determinism: Use GPIO pins that do not emit boot glitches (e.g., GPIO 26, 27, or 33) to prevent the relay from momentarily clicking on power-up. This project uses GPIO 26 and 27.
- AC Wiring: Always switch the Live (Hot) conductor through the relay contacts, leaving Neutral continuous to the load.
Files included in this pack
Esp32 Smart Switch Pack230 KB
Technical Triveni Nodemcu Blynk Relay4.8 KB
Esp32 Smart Switch Pack code5.1 KB
License: MIT
Buy everything at once
Adds all 11 parts to your Amazon.in cart. Check items before you pay.
Before you buy
Match the variant and connector in the note.
Use the component page for the pinout and datasheet.
Prices change daily, so check the final total on Amazon.
Parts list
11 parts. Tick them off as you buy.
As an Amazon Associate I earn from qualifying purchases. Buy links are affiliate links.
11 parts. Tick them off as you buy. As an Amazon Associate I earn from qualifying purchases; buy links are affiliate links.
ESP32 DevKit
Qty 1Mini pump + relay
Qty 1AC Load Switch
Capacitive Touch Sensor Module (e.g., TTP223)
Qty 1Dupont Jumper Wires
Qty 1 packConnections
Breadboard (optional, for prototyping)
Qty 1Prototyping
AC Mains Plug (3-pin)
Qty 1Mains Power Input
AC Mains Socket (2-pin or 3-pin)
Qty 1AC Load Output
2-Core AC Wire (rated for 230V, 5A+)
Qty 2 metersAC Mains Wiring
ESP32 DevKit V1
Qty 1Microcontroller
Also at Robu.in
Mini pump + relay
Qty 1AC Load Actuator
Dupont Jumper Wires
Qty 1 setConnections
Buy everything at once
Adds all 11 parts to your Amazon.in cart. Check items before you pay.
Add all to Amazon cartBefore you buy
Match the variant and connector in the note.
Use the component page for the pinout and datasheet.
Prices change daily, so check the final total on Amazon.
Wiring & circuit connections
Follow the exact circuit connections and pinouts for your board.
Multiple boards supported for this project. Select your board above (e.g. ESP32 DevKit V1 vs AC Mains vs Relay Module) to view the matching pinout & circuit schematic so you don't wire pins incorrectly.
General Connections
| From Pin / Component | To Pin / Board | Connection Note |
|---|---|---|
| ESP32 5V (or 3.3V) | Relay Module VCC | Power for the relay module. Use 5V if available and relay is 5V, otherwise 3.3V. |
| ESP32 GND | Relay Module GND | Common ground connection. |
| ESP32 GPIO 26 | Relay Module IN | Control signal for the relay. |
| ESP32 5V (or 3.3V) | Touch Sensor VCC | Power for the touch sensor. |
| ESP32 GND | Touch Sensor GND | Common ground connection. |
| ESP32 GPIO 27 | Touch Sensor OUT | Input signal from the touch sensor. |
| AC Mains Live | Relay Module COM | Connect the Live wire from mains to the relay's common terminal. |
| Relay Module NO | AC Load Live Input | Connect the Normally Open terminal to the Live input of your appliance. |
| AC Mains Neutral | AC Load Neutral Input | Connect the Neutral wire directly to the appliance. |
ESP32 DevKit V1 Connections
ESP32 DevKit V1| From Pin / Component | To Pin / Board | Connection Note |
|---|---|---|
| 5V | Relay Module VCC | Powers the relay module |
| GND | Relay Module GND | Common ground for relay |
| GPIO 26 | Relay Module IN | Controls the relay (relayPin in code) |
| 5V | Touch Sensor VCC | Powers the touch sensor module |
| GND | Touch Sensor GND | Common ground for touch sensor |
| GPIO 27 | Touch Sensor OUT | Reads touch input (touchPin in code) |
AC Mains Connections
AC Mains| From Pin / Component | To Pin / Board | Connection Note |
|---|---|---|
| Live (Hot) | Relay Module COM | Input Live wire to relay common contact |
| Neutral | AC Load Neutral Input | Direct Neutral connection to appliance |
Relay Module Connections
Relay Module| From Pin / Component | To Pin / Board | Connection Note |
|---|---|---|
| NO (Normally Open) | AC Load Live Input | Switched Live output to appliance |
0 of 9 steps completed0%
2
2. Configure Firmware Credentials and Pins
Open the provided .ino sketch in Arduino IDE. Update BLYNK_TEMPLATE_ID, BLYNK_TEMPLATE_NAME, BLYNK_AUTH_TOKEN, ssid, and pass with your Wi-Fi and Blynk project details. Crucially, change the relayPin to GPIO 26 and touchPin to GPIO 27 for ESP32 compatibility, and update includes to WiFi.h and BlynkSimpleEsp32.h. Set RELAY_ACTIVE_LOW based on your relay module's specification.
3
3. Wire Low-Voltage Control Circuit
Connect the ESP32 to the relay module and touch sensor. Connect ESP32's 3.3V or 5V to the relay's VCC and touch sensor's VCC. Connect ESP32's GND to the relay's GND and touch sensor's GND. Connect ESP32 GPIO 26 to the relay's IN pin. Connect ESP32 GPIO 27 to the touch sensor's OUT pin.
4
4. Flash Firmware and Verify Operation
Connect your ESP32 to your computer via a Micro USB cable. Select the correct COM port in the Arduino IDE and upload the sketch. Open the Serial Monitor (115200 baud) to observe connection status and relay actions. Test the touch sensor and the Blynk app switch (V0) to ensure the relay responds correctly.
5
5. Connect AC Mains Load (DANGER!)
ENSURE MAINS POWER IS DISCONNECTED BEFORE WIRING. Connect the Live (Hot) wire from your AC mains supply to the COM (Common) terminal of the relay. Connect the NO (Normally Open) terminal of the relay to the Live input of your AC load (e.g., an LED bulb holder). Connect the Neutral wire from your AC mains directly to the Neutral input of your AC load. Insulate all exposed AC connections thoroughly. Double-check all wiring before applying power.
6
1. Set Up Arduino IDE and Libraries
Install the Arduino IDE, add ESP32 board support via the Boards Manager, and install the Blynk library from the Library Manager. Ensure you select 'ESP32 Dev Module' from the Tools > Board menu.
7
2. Configure Firmware Credentials and Settings
Open the provided .ino sketch. Replace YOUR_WIFI_SSID, YOUR_WIFI_PASSWORD, YOUR_TEMPLATE_ID, YOUR_TEMPLATE_NAME, and YOUR_NEW_BLYNK_AUTH_TOKEN with your actual Wi-Fi credentials and a newly generated Blynk device token. Adjust RELAY_ACTIVE_LOW to true or false based on your relay module's trigger logic (most common are active-LOW).
8
3. Wire Low-Voltage Components
Connect the ESP32 DevKit V1 to the 1-channel relay module and the capacitive touch sensor module using jumper wires. Ensure all VCC and GND connections are correct before proceeding.
9
5. Connect AC Mains Load (CRITICAL SAFETY STEP)
DANGER: Ensure ALL power is disconnected from the mains outlet and your circuit. Carefully wire the AC mains Live (Hot) wire to the COM terminal of the relay. Connect the NO (Normally Open) terminal of the relay to the Live input of your AC load (e.g., an LED bulb holder). Connect the AC mains Neutral wire directly to the Neutral input of your AC load. Insulate all exposed high-voltage connections thoroughly and place the circuit in a protective enclosure. Only then, plug in the mains cable and test.
1 / 3
ESP32 Blynk IoT Smart Relay Switch
Intermediate2-3 hours
A Wi-Fi-enabled home automation switch using the ESP32 DevKit V1 and Blynk IoT cloud to safely control high-voltage AC appliances from a mobile device.
Safety first, read before building.
Safety notice
This project involves potentially lethal mains voltage. The ESP32 is a low-voltage device, and its GPIO must never be connected directly to 220V AC. Use a correctly rated relay, suitable isolation, a secure enclosure and appropriate electrical protection. Mains-side assembly and verification must be handled by a qualified electrician.
What you will build and learn
Interface an ESP32 microcontroller with the Blynk IoT cloud platform via Wi-Fi
Implement bidirectional communication using Blynk Virtual Pins and event handlers
Safely drive an optoisolated electromechanical relay module from 3.3V logic
Identify and prevent floating state and boot-glitch issues on ESP32 output GPIOs
Prerequisites
Arduino IDE configured with the ESP32 board package and Blynk library, Registered Blynk.Cloud developer account and mobile application, Basic understanding of AC mains electrical safety, fusing, and isolation
System Overview
This project implements an IoT power-switching node using an ESP32 DevKit V1 connected to the Blynk 2.0 Cloud platform. It enables real-time remote switching of AC mains loads (such as an LED bulb) via a smartphone interface.
Architecture & Operating Principle
The signal and power chain functions as follows:
[Blynk Mobile App]
│ (HTTPS/WebSockets)
▼
[Blynk Cloud Platform]
│ (Wi-Fi 802.11 b/g/n @ 2.4 GHz)
▼
[ESP32 DevKit V1]
│ (3.3V / 5V Logic GPIO)
▼
[Optoisolated Relay Module]
│ (Mechanical Dry Contacts: COM & NO)
▼
[220V AC Mains Load (Bulb)]
- Virtual Pin Mapping: The Blynk dashboard uses Virtual Pin
V0configured as an integer datastream (0 or 1). Actuating the mobile switch triggers an event pushed by Blynk Cloud to the ESP32. - Firmware Handling: The ESP32 firmware intercepts state transitions using the
BLYNK_WRITE(V0)macro. The incoming parameter integer (param.asInt()) is evaluated to drive the target output GPIO. - Relay Isolation & Control: The GPIO drives an optocoupler on the relay module. When energized, the relay coil pulls the Normally Open (NO) contact to Common (COM), closing the live conductor of the 220V AC circuit.
Hardware Considerations & Mains Safety
- Galvanic Isolation: The relay's optoisolator prevents high-voltage inductive spikes or ground faults from backfeeding into the ESP32.
- Boot State Determinism: Use GPIO pins that do not emit boot glitches (e.g., GPIO 26, 27, or 33) to prevent the relay from momentarily clicking on power-up. This project uses GPIO 26 and 27.
- AC Wiring: Always switch the Live (Hot) conductor through the relay contacts, leaving Neutral continuous to the load.
Buy everything at once
Adds all 11 parts to your Amazon.in cart. Check items before you pay.
Before you buy
Match the variant and connector in the note.
Use the component page for the pinout and datasheet.
Prices change daily, so check the final total on Amazon.
Parts list
11 parts. Tick them off as you buy.
As an Amazon Associate I earn from qualifying purchases. Buy links are affiliate links.
11 parts. Tick them off as you buy. As an Amazon Associate I earn from qualifying purchases; buy links are affiliate links.
ESP32 DevKit
Qty 1Mini pump + relay
Qty 1AC Load Switch
Capacitive Touch Sensor Module (e.g., TTP223)
Qty 1Dupont Jumper Wires
Qty 1 packConnections
Breadboard (optional, for prototyping)
Qty 1Prototyping
AC Mains Plug (3-pin)
Qty 1Mains Power Input
AC Mains Socket (2-pin or 3-pin)
Qty 1AC Load Output
2-Core AC Wire (rated for 230V, 5A+)
Qty 2 metersAC Mains Wiring
ESP32 DevKit V1
Qty 1Microcontroller
Also at Robu.in
Mini pump + relay
Qty 1AC Load Actuator
Dupont Jumper Wires
Qty 1 setConnections
Buy everything at once
Adds all 11 parts to your Amazon.in cart. Check items before you pay.
Add all to Amazon cartBefore you buy
Match the variant and connector in the note.
Use the component page for the pinout and datasheet.
Prices change daily, so check the final total on Amazon.
Wiring connections
Select your board above to view the matching wiring for your code.
General
ESP32 5V (or 3.3V)→Relay Module VCC
Power for the relay module. Use 5V if available and relay is 5V, otherwise 3.3V.
ESP32 GND→Relay Module GND
Common ground connection.
ESP32 GPIO 26→Relay Module IN
Control signal for the relay.
ESP32 5V (or 3.3V)→Touch Sensor VCC
Power for the touch sensor.
ESP32 GND→Touch Sensor GND
Common ground connection.
ESP32 GPIO 27→Touch Sensor OUT
Input signal from the touch sensor.
AC Mains Live→Relay Module COM
Connect the Live wire from mains to the relay's common terminal.
Relay Module NO→AC Load Live Input
Connect the Normally Open terminal to the Live input of your appliance.
AC Mains Neutral→AC Load Neutral Input
Connect the Neutral wire directly to the appliance.
ESP32 DevKit V1
ESP32 DevKit V15V→Relay Module VCC
Powers the relay module
GND→Relay Module GND
Common ground for relay
GPIO 26→Relay Module IN
Controls the relay (relayPin in code)
5V→Touch Sensor VCC
Powers the touch sensor module
GND→Touch Sensor GND
Common ground for touch sensor
GPIO 27→Touch Sensor OUT
Reads touch input (touchPin in code)
AC Mains
AC MainsLive (Hot)→Relay Module COM
Input Live wire to relay common contact
Neutral→AC Load Neutral Input
Direct Neutral connection to appliance
Relay Module
Relay ModuleNO (Normally Open)→AC Load Live Input
Switched Live output to appliance
0 of 9 steps completed0%
1
1. Prepare Arduino IDE and Libraries
Install the Arduino IDE if you haven't already. Add ESP32 board support via the Boards Manager (search for 'esp32'). Install the Blynk library from the Library Manager (search for 'Blynk').
2
2. Configure Firmware Credentials and Pins
Open the provided .ino sketch in Arduino IDE. Update BLYNK_TEMPLATE_ID, BLYNK_TEMPLATE_NAME, BLYNK_AUTH_TOKEN, ssid, and pass with your Wi-Fi and Blynk project details. Crucially, change the relayPin to GPIO 26 and touchPin to GPIO 27 for ESP32 compatibility, and update includes to WiFi.h and BlynkSimpleEsp32.h. Set RELAY_ACTIVE_LOW based on your relay module's specification.
3
3. Wire Low-Voltage Control Circuit
Connect the ESP32 to the relay module and touch sensor. Connect ESP32's 3.3V or 5V to the relay's VCC and touch sensor's VCC. Connect ESP32's GND to the relay's GND and touch sensor's GND. Connect ESP32 GPIO 26 to the relay's IN pin. Connect ESP32 GPIO 27 to the touch sensor's OUT pin.
4
4. Flash Firmware and Verify Operation
Connect your ESP32 to your computer via a Micro USB cable. Select the correct COM port in the Arduino IDE and upload the sketch. Open the Serial Monitor (115200 baud) to observe connection status and relay actions. Test the touch sensor and the Blynk app switch (V0) to ensure the relay responds correctly.
5
5. Connect AC Mains Load (DANGER!)
ENSURE MAINS POWER IS DISCONNECTED BEFORE WIRING. Connect the Live (Hot) wire from your AC mains supply to the COM (Common) terminal of the relay. Connect the NO (Normally Open) terminal of the relay to the Live input of your AC load (e.g., an LED bulb holder). Connect the Neutral wire from your AC mains directly to the Neutral input of your AC load. Insulate all exposed AC connections thoroughly. Double-check all wiring before applying power.
6
1. Set Up Arduino IDE and Libraries
Install the Arduino IDE, add ESP32 board support via the Boards Manager, and install the Blynk library from the Library Manager. Ensure you select 'ESP32 Dev Module' from the Tools > Board menu.
7
2. Configure Firmware Credentials and Settings
Open the provided .ino sketch. Replace YOUR_WIFI_SSID, YOUR_WIFI_PASSWORD, YOUR_TEMPLATE_ID, YOUR_TEMPLATE_NAME, and YOUR_NEW_BLYNK_AUTH_TOKEN with your actual Wi-Fi credentials and a newly generated Blynk device token. Adjust RELAY_ACTIVE_LOW to true or false based on your relay module's trigger logic (most common are active-LOW).
8
3. Wire Low-Voltage Components
Connect the ESP32 DevKit V1 to the 1-channel relay module and the capacitive touch sensor module using jumper wires. Ensure all VCC and GND connections are correct before proceeding.
9
5. Connect AC Mains Load (CRITICAL SAFETY STEP)
DANGER: Ensure ALL power is disconnected from the mains outlet and your circuit. Carefully wire the AC mains Live (Hot) wire to the COM terminal of the relay. Connect the NO (Normally Open) terminal of the relay to the Live input of your AC load (e.g., an LED bulb holder). Connect the AC mains Neutral wire directly to the Neutral input of your AC load. Insulate all exposed high-voltage connections thoroughly and place the circuit in a protective enclosure. Only then, plug in the mains cable and test.
