💧 Introduction to TDS Sensor

A TDS Sensor (Total Dissolved Solids Sensor) is an electronic sensor used to measure the amount of dissolved substances in water.

These dissolved substances may include:

• Salts

• Minerals

• Metals

• Organic matter

• Impurities

The sensor measures water purity and gives the result in:

PPM (Parts Per Million)

🔬 What is TDS?

TDS stands for:

Total Dissolved Solids

It represents the total concentration of dissolved particles in water.

Example:
If water contains 200 mg of dissolved solids in 1 liter of water,
then TDS = 200 ppm.

📊 TDS Water Quality Classification

WHO recommended drinking water:
✔ Below 300 ppm

⚙ Working Principle of TDS Sensor

                     

TDS sensor works on the principle of:

Electrical Conductivity

Explanation:

1️⃣ Pure water conducts very little electricity
2️⃣ Dissolved salts and minerals increase conductivity
3️⃣ More dissolved solids → More electrical conductivity
4️⃣ Sensor measures conductivity
5️⃣ Converts it into voltage
6️⃣ Microcontroller converts voltage into PPM value

🔌 Parts of Analog TDS Sensor Module

Most analog TDS modules consist of:

🔹 1️⃣ TDS Probe

• Two electrodes

• Placed in water

• Measures conductivity

🔹 2️⃣ Signal Conditioning Board

• Amplifies signal

• Converts conductivity to analog voltage

• Provides stable output

📌 Pin Configuration

AO gives voltage proportional to TDS value.

🧠 How ESP32 Uses TDS Sensor

1️⃣ ESP32 reads analog voltage (0–3.3V)
2️⃣ Converts ADC value (0–4095)
3️⃣ Applies calibration formula
4️⃣ Calculates TDS value in PPM
5️⃣ Displays on Serial / IoT Dashboard

📐 Basic TDS Calculation Formula

Typical formula used:

Voltage = ADC_Value × (3.3 / 4095)

TDS = (133.42 × V³ – 255.86 × V² + 857.39 × V) × 0.5

Where:
V = Sensor output voltage

This formula converts voltage to TDS (ppm).

🌍 Applications of TDS Sensor

• Drinking water monitoring

• RO filter monitoring

• Water purification plants

• Aquarium water monitoring

• Fish farming

• River water testing

• Smart city water systems

⚖ Advantages of TDS Sensor

✔ Easy to use
✔ Low cost
✔ Analog output
✔ Compatible with ESP32
✔ Real-time measurement

⚠ Limitations of TDS Sensor

⚠ Does not identify specific contaminants
⚠ Temperature affects reading
⚠ Needs calibration
⚠ Cannot detect bacteria

TDS measures quantity of dissolved solids,
not the type of impurity.

🎯 What Students Will Learn

After this lesson, students will understand:

• What TDS means

• How water purity is measured

• Conductivity concept

• Voltage to PPM conversion

• Environmental monitoring systems

📌 Lesson Summary

A TDS Sensor measures the total dissolved solids in water by detecting electrical conductivity.

Higher dissolved solids → Higher conductivity → Higher PPM value.

It is widely used in:

• Water quality monitoring

• RO plants

• Environmental IoT systems

This sensor forms the foundation of our:

💧 Smart Water Quality Monitoring System (Module 8)