W14 — Interface & Application Programming

Navigate to blynk.io and log in or create a free account. The Blynk Console is the main web interface where you configure templates, datastreams, and dashboards before deploying your project.

Once logged in you land on the main console, where you manage all your connected devices and projects. The next step is creating a Template that describes your hardware and its behaviour.

A Template is the blueprint for a device type. It defines the hardware model, connection method, datastreams, and dashboard layout. Every physical device is then registered against a template.

1. In the left sidebar, click Developer Zone.
2. Select Templates, then click + New Template.
3. Fill in: Name (e.g. "LED On and Off"), Hardware (ESP32), Connection Type (WiFi).
4. Click Done to save.

A Datastream is the data channel between your hardware and the Blynk cloud. For an LED, you create a Digital Pin datastream that maps to a GPIO pin on your microcontroller.

1. Inside your template, click the Datastreams tab.
2. Click + New Datastream and select Digital Pin.
3. Set the Name (e.g. "LED Pin 4") and Pin (D4 / GPIO 4).
4. Leave Data Type as Integer (0 = OFF, 1 = ON), then click Create.

The Web Dashboard provides a browser-based interface to interact with your device. You add a Switch widget to toggle the LED on and off with a single click.

1. Click the Web Dashboard tab within your template.
2. In the widget panel on the right, locate the Switch widget.
3. Drag the Switch onto the dashboard canvas and position it.
4. Click the widget to open its settings — set the Title to "LED" and the Datastream to "LED Pin 4".
5. Click Save.

Once the dashboard and widgets are configured, save the template, then register a physical device against it. This generates the unique Auth Token needed in the firmware.

1. Click Save at the top-right of the template editor.
2. In the sidebar, click Devices → + New Device.
3. Choose From Template and select your template.
4. Enter a device name (LED On and Off") and click Create.
5. Copy the Template ID, Device Name, and Auth Token — all three are required in the firmware.

With the device registered, flash firmware to the ESP32 so it connects to Blynk over Wi-Fi and responds to dashboard commands.

Install the Blynk Library

Open the Arduino IDE → Sketch → Include Library → Manage Libraries… → search "Blynk" → install Blynk by Volodymyr Shymanskyy.

Complete Arduino Sketch

Replace the Wi-Fi credentials and Blynk credentials with the values from your device page.

// These MUST be at the very top, before any #include
#define BLYNK_TEMPLATE_ID   "TMPL6yFluiTJG"
#define BLYNK_TEMPLATE_NAME "LED On and Off"
#define BLYNK_AUTH_TOKEN    "YourAuthTokenHere"
#define BLYNK_PRINT Serial

#include <WiFi.h>
#include <WiFiClient.h>
#include <BlynkSimpleEsp32.h>

// Wi-Fi credentials
char ssid[] = "YourWiFiName";
char pass[] = "YourWiFiPassword";

#define LED_PIN 4  // GPIO 4

// Called whenever the Blynk dashboard writes to Virtual Pin V0
BLYNK_WRITE(V0) {
  int value = param.asInt();    // 0 = OFF, 1 = ON
  digitalWrite(LED_PIN, value);
  Serial.print("LED set to: ");
  Serial.println(value);
}

void setup() {
  Serial.begin(115200);
  pinMode(LED_PIN, OUTPUT);
  digitalWrite(LED_PIN, LOW);   // Start with LED off
  Blynk.begin(BLYNK_AUTH_TOKEN, ssid, pass);
}

void loop() {
  Blynk.run();
}

The Blynk mobile app (iOS and Android) mirrors the web dashboard, letting you control your hardware from your smartphone anywhere with an internet connection.

1. Download the Blynk IoT app from the App Store or Google Play.
2. Sign in with the same account used for the Blynk Console.
3. Your device and dashboard appear automatically — no additional setup needed.
4. Tap the Switch widget on your phone to toggle the LED on the ESP32.

App Tutorial Video