#include <WiFi.h>

#define TDS_PIN 34

const char* ssid = "Water_Quality_AP";
const char* password = "12345678";

WiFiServer server(23);

float voltage = 0;
float tdsValue = 0;

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

WiFi.softAP(ssid, password);

Serial.println("Hotspot Started");
Serial.print("AP IP Address: ");
Serial.println(WiFi.softAPIP());

server.begin();
Serial.println("TCP Server Started on Port 23");
}

void loop() {

WiFiClient client = server.available();

if (client) {
Serial.println("Client Connected");

client.println("=== Water Quality Monitoring ===");

while (client.connected()) {

int adcValue = analogRead(TDS_PIN);

voltage = adcValue * (3.3 / 4095.0);

tdsValue = (133.42 * voltage * voltage * voltage 
- 255.86 * voltage * voltage 
+ 857.39 * voltage) * 0.5;

client.print("TDS Value: ");
client.print(tdsValue);
client.print(" ppm");

if (tdsValue < 50) {
client.println(" | Very Pure Water");
}
else if (tdsValue < 150) {
client.println(" | Excellent Water");
}
else if (tdsValue < 300) {
client.println(" | Good Water");
}
else if (tdsValue < 500) {
client.println(" | Fair Water");
}
else {
client.println(" | Poor / Unsafe Water");
}

delay(2000);
}

client.stop();
Serial.println("Client Disconnected");
}
}

🧠 Code Explanation

1️⃣ Enable Hotspot Mode

ESP32 creates its own WiFi network:

Network Name:

Password:

Default IP:

2️⃣ Create TCP Server

Creates Telnet server on Port 23.

Mobile connects using:

• Host: 192.168.4.1

• Port: 23

3️⃣ Read Analog Value

Reads sensor voltage.

4️⃣ Convert Voltage to TDS

Converts voltage to PPM.

5️⃣ Water Quality Classification

Based on TDS value:

📱 How To Use

Step 1
Upload code

Step 2
Open Serial Monitor
Note IP address (usually 192.168.4.1)

Step 3
Connect mobile WiFi to:

Step 4
Open TCP Terminal App

Enter:

• Host: 192.168.4.1

• Port: 23

Step 5
View live TDS value

📟 Example Output

🎯 What Students Learn

• ESP32 Access Point Mode

• TCP server communication

• Analog sensor reading

• Wireless data transmission

• Environmental IoT system

📌 Lesson Summary

In this lesson, students built a:

💧 WiFi Hotspot-Based Water Quality Monitoring System

The system:

✔ Measures TDS
✔ Classifies water quality
✔ Sends data wirelessly
✔ Works without router