#define BLYNK_TEMPLATE_ID "YOUR_TEMPLATE_ID"
#define BLYNK_DEVICE_NAME "Ultrasonic Water System"
#define BLYNK_AUTH_TOKEN "YOUR_AUTH_TOKEN"

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

#define TRIG_PIN 5
#define ECHO_PIN 18
#define RELAY_PIN 26

char ssid[] = "YOUR_WIFI_NAME";
char pass[] = "YOUR_WIFI_PASSWORD";

float tankHeight = 30.0;
long duration;
float distance;
float waterLevel;
float percentage;

bool autoMode = true;
bool motorState = false;

BLYNK_WRITE(V0) {
autoMode = param.asInt();
}

BLYNK_WRITE(V1) {
if (!autoMode) {
int value = param.asInt();
if (value == 1) turnMotorOn();
else turnMotorOff();
}
}

void setup() {
Serial.begin(115200);

pinMode(TRIG_PIN, OUTPUT);
pinMode(ECHO_PIN, INPUT);
pinMode(RELAY_PIN, OUTPUT);

digitalWrite(RELAY_PIN, HIGH);

Blynk.begin(BLYNK_AUTH_TOKEN, ssid, pass);
}

void loop() {
Blynk.run();

// Ultrasonic measurement
digitalWrite(TRIG_PIN, LOW);
delayMicroseconds(2);
digitalWrite(TRIG_PIN, HIGH);
delayMicroseconds(10);
digitalWrite(TRIG_PIN, LOW);

duration = pulseIn(ECHO_PIN, HIGH);
distance = duration * 0.034 / 2;

waterLevel = tankHeight - distance;

if (waterLevel < 0) waterLevel = 0;
if (waterLevel > tankHeight) waterLevel = tankHeight;

percentage = (waterLevel / tankHeight) * 100;

Blynk.virtualWrite(V2, percentage);

if (autoMode) {

if (percentage < 20 && !motorState) {
turnMotorOn();
}

if (percentage > 90 && motorState) {
turnMotorOff();
Blynk.virtualWrite(V3, 1);
} else {
Blynk.virtualWrite(V3, 0);
}
}
}

void turnMotorOn() {
digitalWrite(RELAY_PIN, LOW);
motorState = true;
Blynk.virtualWrite(V1, 1);
}

void turnMotorOff() {
digitalWrite(RELAY_PIN, HIGH);
motorState = false;
Blynk.virtualWrite(V1, 0);
}

🧠 Code Explanation

1️⃣ BLYNK_WRITE(V0)

Controls Auto/Manual mode from dashboard.

If:

• 1 → Auto Mode

• 0 → Manual Mode

2️⃣ BLYNK_WRITE(V1)

Controls motor manually only when Auto mode is OFF.

3️⃣ Ultrasonic Measurement

Converts echo time into distance.

4️⃣ Tank Percentage Calculation

Calculates water percentage.

5️⃣ Dashboard Updates

Updates tank percentage display.

Turns ON tank FULL LED.

6️⃣ Auto Mode Logic

If tank < 20%
→ Motor ON

If tank > 90%
→ Motor OFF + LED ON

📟 System Working Flow

1. ESP32 connects to WiFi

2. Connects to Blynk Cloud

3. Reads ultrasonic sensor

4. Calculates tank percentage

5. Checks mode

6. Controls motor

7. Updates dashboard

🎯 What Students Learn

• Cloud-based IoT architecture

• Virtual pin concept

• Ultrasonic measurement logic

• Remote automation system

• Auto + Manual design

• Real-world IoT implementation