Measuring Water Quality: Arduino TDS Sensor Interface Tutorial

In this tutorial, we will learn how to interface Arduino with a TDS sensor to measure water quality. TDS sensors measure the concentration of total dissolved solids in a solution, which measures water purity.

Water is more important for life, and the quality of drinking water matters. Pure water contains minerals, while distilled water is devoid of any elements. The taste of water, whether bitter or sweet, is influenced by added minerals and impurities. Total Dissolved Solids (TDS) in water define its taste and composition.

The higher the TDS level, the more impurities are present in the water. By the end of this tutorial, you will have a better understanding of how TDS sensors work and how to interface with them using an Arduino. Checkout our recent post Arduino Flow Sensor Tutorial: How to Measure Liquid Flow

Required Material

Arduino Nano or UNO
TDS sensor
Jumper wires
USB cable
Breadboard

What is a TDS sensor

A TDS meter measures total dissolved solids such as salts, minerals, and metals in water. As these solids increase, water conductivity increases, helping the calculation of total dissolved solids in ppm (mg/L).

However, while this acts as a good indicator for monitoring water quality, it’s important to note that it doesn’t detect water impurities.

TDS meters are good for monitoring water quality in different locations like pools, aquariums, hydroponics, and water purifiers.

TDS chart

TDS sensor for Arduino

TDS Sensor Specs

Wide Voltage Input: Accepts 3.3~5V power input.
Good Compatibility Output: Offers 0~2.3V analog signal output
Waterproof Probe: Provides improved durability.
Ease of Use: Arduino compatible, allows easy plug-and-play.

TDS Meter:

- Input Voltage: DC 3.3 ~ 5V
- Output Voltage: 0 ~ 2.3V
- Working Current: 3 ~ 6mA
- TDS Measurement Range: 0 ~ 1000ppm
- TDS Measurement Accuracy: ±10% F.S. (25 ℃)
- Module Interface: XH2.54-3P
- Electrode Interface: XH2.54-2P
TDS Probe:

- Number of Needles: 2
- Total Length: 60cm
- Connection Interface: XH2.54-2P
- Color: White
- Waterproof Probe for added durability

TDS Sensor Pinout

Interfacing TDS Sensor With Arduino

We will interface the TDS sensor with Arduino and display the TDS value on an OLED Display. TDS sensor fullforms Total Dissolved Solids, and it is a measure of the dissolved minerals in water.

Circuit Connection:

TDS Sensor Pin	Arduino Pin
GND	GND
VCC	3.3V
Data	A0 (or any other Arduino analog pin)

Example Arduino TDS Sensor Code

#define TdsSensorPin A0
#define VREF 5.0 // analog reference voltage(Volt) of the ADC
#define SCOUNT 30 // sum of sample point
int analogBuffer[SCOUNT]; // store the analog value in the array, read from ADC
int analogBufferTemp[SCOUNT];
int analogBufferIndex = 0,copyIndex = 0;
float averageVoltage = 0,tdsValue = 0,temperature = 25;
void setup()
{
Serial.begin(115200);
pinMode(TdsSensorPin,INPUT);
}
void loop()
{
static unsigned long analogSampleTimepoint = millis();
if(millis()-analogSampleTimepoint > 40U) //every 40 milliseconds,read the analog value from the ADC
{
analogSampleTimepoint = millis();
analogBuffer[analogBufferIndex] = analogRead(TdsSensorPin); //read the analog value and store into the buffer
analogBufferIndex++;
if(analogBufferIndex == SCOUNT)
analogBufferIndex = 0;
}
static unsigned long printTimepoint = millis();
if(millis()-printTimepoint > 800U)
{
printTimepoint = millis();
for(copyIndex=0;copyIndex<SCOUNT;copyIndex++)
analogBufferTemp[copyIndex]= analogBuffer[copyIndex];
averageVoltage = getMedianNum(analogBufferTemp,SCOUNT) * (float)VREF/ 1024.0; // read the analog value more stable by the median filtering algorithm, and convert to voltage value
float compensationCoefficient=1.0+0.02*(temperature-25.0); //temperature compensation formula: fFinalResult(25^C) = fFinalResult(current)/(1.0+0.02*(fTP-25.0));
float compensationVolatge=averageVoltage/compensationCoefficient; //temperature compensation
tdsValue=(133.42*compensationVolatge*compensationVolatge*compensationVolatge - 255.86*compensationVolatge*compensationVolatge + 857.39*compensationVolatge)*0.5; //convert voltage value to tds value
//Serial.print("voltage:");
//Serial.print(averageVoltage,2);
//Serial.print("V ");
Serial.print("TDS Value:");
Serial.print(tdsValue,0);
Serial.println("ppm");
}
}
int getMedianNum(int bArray[], int iFilterLen)
{
int bTab[iFilterLen];
for (byte i = 0; i<iFilterLen; i++)
bTab[i] = bArray[i];
int i, j, bTemp;
for (j = 0; j < iFilterLen - 1; j++)
{
for (i = 0; i < iFilterLen - j - 1; i++)
{
if (bTab[i] > bTab[i + 1])
{
bTemp = bTab[i];
bTab[i] = bTab[i + 1];
bTab[i + 1] = bTemp;
}
}
}
if ((iFilterLen & 1) > 0)
bTemp = bTab[(iFilterLen - 1) / 2];
else
bTemp = (bTab[iFilterLen / 2] + bTab[iFilterLen / 2 - 1]) / 2;
return bTemp;
}

#define TdsSensorPin A0

#define VREF 5.0 // analog reference voltage(Volt) of the ADC

#define SCOUNT 30 // sum of sample point

int analogBuffer[SCOUNT]; // store the analog value in the array, read from ADC

int analogBufferTemp[SCOUNT];

int analogBufferIndex = 0,copyIndex = 0;

float averageVoltage = 0,tdsValue = 0,temperature = 25;

void setup()

{

Serial.begin(115200);

pinMode(TdsSensorPin,INPUT);

}

void loop()

{

static unsigned long analogSampleTimepoint = millis();

if(millis()-analogSampleTimepoint > 40U) //every 40 milliseconds,read the analog value from the ADC

{

analogSampleTimepoint = millis();

analogBuffer[analogBufferIndex] = analogRead(TdsSensorPin); //read the analog value and store into the buffer

analogBufferIndex++;

if(analogBufferIndex == SCOUNT)

analogBufferIndex = 0;

}

static unsigned long printTimepoint = millis();

if(millis()-printTimepoint > 800U)

{

printTimepoint = millis();

for(copyIndex=0;copyIndex<SCOUNT;copyIndex++)

analogBufferTemp[copyIndex]= analogBuffer[copyIndex];

averageVoltage = getMedianNum(analogBufferTemp,SCOUNT) * (float)VREF/ 1024.0; // read the analog value more stable by the median filtering algorithm, and convert to voltage value

float compensationCoefficient=1.0+0.02*(temperature-25.0); //temperature compensation formula: fFinalResult(25^C) = fFinalResult(current)/(1.0+0.02*(fTP-25.0));

float compensationVolatge=averageVoltage/compensationCoefficient; //temperature compensation

tdsValue=(133.42*compensationVolatge*compensationVolatge*compensationVolatge - 255.86*compensationVolatge*compensationVolatge + 857.39*compensationVolatge)*0.5; //convert voltage value to tds value

//Serial.print("voltage:");

//Serial.print(averageVoltage,2);

//Serial.print("V ");

Serial.print("TDS Value:");

Serial.print(tdsValue,0);

Serial.println("ppm");

}

int getMedianNum(int bArray[], int iFilterLen)

{

int bTab[iFilterLen];

for (byte i = 0; i<iFilterLen; i++)

bTab[i] = bArray[i];

int i, j, bTemp;

for (j = 0; j < iFilterLen - 1; j++)

{

for (i = 0; i < iFilterLen - j - 1; i++)

{

if (bTab[i] > bTab[i + 1])

{

bTemp = bTab[i];

bTab[i] = bTab[i + 1];

bTab[i + 1] = bTemp;

}

if ((iFilterLen & 1) > 0)

bTemp = bTab[(iFilterLen - 1) / 2];

else

bTemp = (bTab[iFilterLen / 2] + bTab[iFilterLen / 2 - 1]) / 2;

return bTemp;

}

Test Summary

Code Upload: Code successfully uploaded.
Open serial monitor at 115200 baud rate.
Setup: Place the TDS probe in water for measurement.

Result: Monitor displays TDS value.

Calibrate TDS Measurement Accuracy with Arduino

In the basic tutorial, measuring TDS in liquids is easy but can have errors due to differences in probes and control boards, and lack of temperature balance.

For accuracy, calibrate before measuring. Adding a temp sensor helps. TDS is usually half the EC value:

TDS = EC / 2

It’s the same diagram as the basic. For calibration, use a known solution like 1413us/cm buffer (around 707 ppm as TDS). Use a TDS pen if no buffer.

Download and install the DFRobot Gravity TDS Sensor Library for Arduino.

Sample Code

/***************************************************
 DFRobot Gravity: Analog TDS Sensor/Meter
 <https://www.dfrobot.com/wiki/index.php/Gravity:_Analog_TDS_Sensor_/_Meter_For_Arduino_SKU:_SEN0244>
 
 ***************************************************
 This sample code shows how to read the tds value and calibrate it with the standard buffer solution.
 707ppm(1413us/cm)@25^c standard buffer solution is recommended.
 
 Created 2018-1-3
 By Jason <jason.ling@dfrobot.com@dfrobot.com>
 
 GNU Lesser General Public License.
 See <http://www.gnu.org/licenses/> for details.
 All above must be included in any redistribution.
 ****************************************************/
 
 /***********Notice and Trouble shooting***************
 1. This code is tested on Arduino Uno with Arduino IDE 1.0.5 r2 and 1.8.2.
 2. Calibration CMD:
     enter -> enter the calibration mode
     cal:tds value -> calibrate with the known tds value(25^c). e.g.cal:707
     exit -> save the parameters and exit the calibration mode
 ****************************************************/
 
#include <EEPROM.h>
#include "GravityTDS.h"
 
#define TdsSensorPin A0
GravityTDS gravityTds;
 
float temperature = 25,tdsValue = 0;
 
void setup()
{
    Serial.begin(115200);
    gravityTds.setPin(TdsSensorPin);
    gravityTds.setAref(5.0);  //reference voltage on ADC, default 5.0V on Arduino UNO
    gravityTds.setAdcRange(1024);  //1024 for 10bit ADC;4096 for 12bit ADC
    gravityTds.begin();  //initialization
}
 
void loop()
{
    //temperature = readTemperature();  //add your temperature sensor and read it
    gravityTds.setTemperature(temperature);  // set the temperature and execute temperature compensation
    gravityTds.update();  //sample and calculate
    tdsValue = gravityTds.getTdsValue();  // then get the value
    Serial.print(tdsValue,0);
    Serial.println("ppm");
    delay(1000);
}

/***************************************************

DFRobot Gravity: Analog TDS Sensor/Meter

<https://www.dfrobot.com/wiki/index.php/Gravity:_Analog_TDS_Sensor_/_Meter_For_Arduino_SKU:_SEN0244>

***************************************************

This sample code shows how to read the tds value and calibrate it with the standard buffer solution.

707ppm(1413us/cm)@25^c standard buffer solution is recommended.

Created 2018-1-3

By Jason <jason.ling@dfrobot.com@dfrobot.com>

GNU Lesser General Public License.

See <http://www.gnu.org/licenses/> for details.

All above must be included in any redistribution.

****************************************************/

/***********Notice and Trouble shooting***************

1. This code is tested on Arduino Uno with Arduino IDE 1.0.5 r2 and 1.8.2.

2. Calibration CMD:

enter -> enter the calibration mode

cal:tds value -> calibrate with the known tds value(25^c). e.g.cal:707

exit -> save the parameters and exit the calibration mode

****************************************************/

#include <EEPROM.h>

#include "GravityTDS.h"

#define TdsSensorPin A0

GravityTDS gravityTds;

float temperature = 25,tdsValue = 0;

void setup()

{

Serial.begin(115200);

gravityTds.setPin(TdsSensorPin);

gravityTds.setAref(5.0); //reference voltage on ADC, default 5.0V on Arduino UNO

gravityTds.setAdcRange(1024); //1024 for 10bit ADC;4096 for 12bit ADC

gravityTds.begin(); //initialization

}

void loop()

{

//temperature = readTemperature(); //add your temperature sensor and read it

gravityTds.setTemperature(temperature); // set the temperature and execute temperature compensation

gravityTds.update(); //sample and calculate

tdsValue = gravityTds.getTdsValue(); // then get the value

Serial.print(tdsValue,0);

Serial.println("ppm");

delay(1000);

}

Calibrating the TDS Meter:

Upload the above sample code onto your Arduino and open the serial monitor.
First Clean and dry the TDS probe with blotting paper.
Insert the probe into an available electrical conductivity or TDS value buffer solution, stir gently, and wait for stable readings.
Use a TDS pen to measure
the water TDS value.
Enter the “enter” command to start calibration mode.

Enter the “cal:tds value” command. For example, use “cal:120” for a 120ppm buffer solution.

Input “exit“ to save and exit calibration mode.

Now the TDS sensor is ready for use in your application.

Monitor Water Quality Using Arduino and TDS Sensor & OLED

Arduino	OLED Display	TDS Sensor
GND	GND	GND
5V	VCC	VCC
A4 (SDA)	SDA	–
A5 (SCL)	SCL	–
A0	–	Signal (Analog)

Source Code Monitor Water Quality Using Arduino and TDS Sensor

#include <Wire.h>
#include <Adafruit_GFX.h>
#include <Adafruit_SSD1306.h>

#define OLED_RESET 1
Adafruit_SSD1306 display(128, 64, &Wire, OLED_RESET);

#define TdsSensorPin A0
#define VREF 5.0      // Analog reference voltage(Volt) of the ADC
#define SCOUNT  30    // Sum of sample points

// Store the analog values in arrays read from ADC
int analogBuffer[SCOUNT];
int analogBufferTemp[SCOUNT];
int analogBufferIndex = 0, copyIndex = 0;
float averageVoltage = 0, tdsValue = 0, temperature = 25;

void setup() {
    Serial.begin(115200);
    pinMode(TdsSensorPin, INPUT);
    Wire.begin();
    display.begin(SSD1306_SWITCHCAPVCC, 0x3C);
    display.clearDisplay();
}

void loop() {
    static unsigned long analogSampleTimepoint = millis();

    // Read the analog value from the ADC every 40 milliseconds
    if (millis() - analogSampleTimepoint > 40U) {
        analogSampleTimepoint = millis();
        analogBuffer[analogBufferIndex] = analogRead(TdsSensorPin);
        analogBufferIndex++;
        if (analogBufferIndex == SCOUNT)
            analogBufferIndex = 0;
    }

    static unsigned long printTimepoint = millis();

    // Print TDS value every 800 milliseconds
    if (millis() - printTimepoint > 800U) {
        printTimepoint = millis();

        // Copy analog buffer for processing
        for (copyIndex = 0; copyIndex < SCOUNT; copyIndex++)
            analogBufferTemp[copyIndex] = analogBuffer[copyIndex];

        // Obtain a more stable analog value by median filtering algorithm
        averageVoltage = getMedianNum(analogBufferTemp, SCOUNT) * (float)VREF / 1024.0;

        // Temperature compensation formula
        float compensationCoefficient = 1.0 + 0.02 * (temperature - 25.0);
        float compensationVoltage = averageVoltage / compensationCoefficient;

        // Convert voltage value to TDS value
        tdsValue = (133.42 * compensationVoltage * compensationVoltage * compensationVoltage - 255.86 * compensationVoltage * compensationVoltage + 857.39 * compensationVoltage) * 0.5;

        // Print TDS value via Serial
        Serial.print("TDS Value:");
        Serial.print(tdsValue, 0);
        Serial.println("ppm");

        // Display TDS value on OLED
        display.clearDisplay();
        display.setTextSize(2);
        display.setTextColor(WHITE);
        display.setCursor(0, 0);
        display.print("TDS Value:");
        display.display();

        display.setTextSize(2);
        display.setTextColor(WHITE);
        display.setCursor(30, 30);
        display.print(tdsValue, 0);
        display.setCursor(80, 28);
        display.print("ppm");
        display.display();
        // Display "Water Quality" below ppm value
        display.setTextSize(1); // Changing text size to fit below ppm
        display.setTextColor(WHITE);
        display.setCursor(30, 50); // Adjust the cursor position as needed
        display.print("Water Quality");
        display.display();
    }
}

// Median filter function
int getMedianNum(int bArray[], int iFilterLen) {
    int bTab[iFilterLen];
    for (byte i = 0; i < iFilterLen; i++)
        bTab[i] = bArray[i];

    int i, j, bTemp;
    for (j = 0; j < iFilterLen - 1; j++) {
        for (i = 0; i < iFilterLen - j - 1; i++) {
            if (bTab[i] > bTab[i + 1]) {
                bTemp = bTab[i];
                bTab[i] = bTab[i + 1];
                bTab[i + 1] = bTemp;
            }
        }
    }

    if ((iFilterLen & 1) > 0)
        bTemp = bTab[(iFilterLen - 1) / 2];
    else
        bTemp = (bTab[iFilterLen / 2] + bTab[iFilterLen / 2 - 1]) / 2;

    return bTemp;
}

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#include <Wire.h>

#include <Adafruit_GFX.h>

#include <Adafruit_SSD1306.h>

#define OLED_RESET 1

Adafruit_SSD1306 display(128, 64, &Wire, OLED_RESET);

#define TdsSensorPin A0

#define VREF 5.0 // Analog reference voltage(Volt) of the ADC

#define SCOUNT 30 // Sum of sample points

// Store the analog values in arrays read from ADC

int analogBuffer[SCOUNT];

int analogBufferTemp[SCOUNT];

int analogBufferIndex = 0, copyIndex = 0;

float averageVoltage = 0, tdsValue = 0, temperature = 25;

void setup() {

Serial.begin(115200);

pinMode(TdsSensorPin, INPUT);

Wire.begin();

display.begin(SSD1306_SWITCHCAPVCC, 0x3C);

display.clearDisplay();

}

void loop() {

static unsigned long analogSampleTimepoint = millis();

// Read the analog value from the ADC every 40 milliseconds

if (millis() - analogSampleTimepoint > 40U) {

analogSampleTimepoint = millis();

analogBuffer[analogBufferIndex] = analogRead(TdsSensorPin);

analogBufferIndex++;

if (analogBufferIndex == SCOUNT)

analogBufferIndex = 0;

}

static unsigned long printTimepoint = millis();

// Print TDS value every 800 milliseconds

if (millis() - printTimepoint > 800U) {

printTimepoint = millis();

// Copy analog buffer for processing

for (copyIndex = 0; copyIndex < SCOUNT; copyIndex++)

analogBufferTemp[copyIndex] = analogBuffer[copyIndex];

// Obtain a more stable analog value by median filtering algorithm

averageVoltage = getMedianNum(analogBufferTemp, SCOUNT) * (float)VREF / 1024.0;

// Temperature compensation formula

float compensationCoefficient = 1.0 + 0.02 * (temperature - 25.0);

float compensationVoltage = averageVoltage / compensationCoefficient;

// Convert voltage value to TDS value

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

// Print TDS value via Serial

Serial.print("TDS Value:");

Serial.print(tdsValue, 0);

Serial.println("ppm");

// Display TDS value on OLED

display.clearDisplay();

display.setTextSize(2);

display.setTextColor(WHITE);

display.setCursor(0, 0);

display.print("TDS Value:");

display.display();

display.setTextSize(2);

display.setTextColor(WHITE);

display.setCursor(30, 30);

display.print(tdsValue, 0);

display.setCursor(80, 28);

display.print("ppm");

display.display();

// Display "Water Quality" below ppm value

display.setTextSize(1); // Changing text size to fit below ppm

display.setTextColor(WHITE);

display.setCursor(30, 50); // Adjust the cursor position as needed

display.print("Water Quality");

display.display();

}

// Median filter function

int getMedianNum(int bArray[], int iFilterLen) {

int bTab[iFilterLen];

for (byte i = 0; i < iFilterLen; i++)

bTab[i] = bArray[i];

int i, j, bTemp;

for (j = 0; j < iFilterLen - 1; j++) {

for (i = 0; i < iFilterLen - j - 1; i++) {

if (bTab[i] > bTab[i + 1]) {

bTemp = bTab[i];

bTab[i] = bTab[i + 1];

bTab[i + 1] = bTemp;

}

if ((iFilterLen & 1) > 0)

bTemp = bTab[(iFilterLen - 1) / 2];

else

bTemp = (bTab[iFilterLen / 2] + bTab[iFilterLen / 2 - 1]) / 2;

return bTemp;

}

If the probe isn’t in the water, it displays around 0. Dip it in liquids to check their TDS. Try tap water and add salt to see higher values

I tested distilled water—it measured 90-95 ppm. Then, I tried tap water, which showed 250+ ppm.

After adding salt to the distilled water, it spiked to 1300 ppm.

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Measuring Water Quality: Arduino TDS Sensor Interface Tutorial

Required Material

What is a TDS sensor

TDS chart

TDS sensor for Arduino

TDS Sensor Specs

TDS Sensor Pinout

Interfacing TDS Sensor With Arduino

Example Arduino TDS Sensor Code

Test Summary

Calibrate TDS Measurement Accuracy with Arduino

Sample Code

Monitor Water Quality Using Arduino and TDS Sensor & OLED

Source Code Monitor Water Quality Using Arduino and TDS Sensor

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