CharityHackathon

Using TCS34725 for Chlorine Detection

The Principle

Chlorine detection with RGB sensors relies on colorimetric testing - using chemical reagents that change color in the presence of chlorine:

1. DPD (N,N-diethyl-p-phenylenediamine) - turns pink/red with chlorine

2. OTO (Orthotolidine) - turns yellow with chlorine

Major Limitations

1. Requires chemical reagents (DPD or OTO)

2. Not direct measurement - measures color change, not chlorine

3. Affected by:

   • Water turbidity

   • pH levels

   • Temperature

   • Other chemicals

   • Ambient light

4. Accuracy issues - ±0.5 ppm at best

Better Alternatives for Chlorine Detection

1. Electrochemical Sensors (Recommended)

Professional Sensors

• FCL-01 - Free chlorine sensor

• CLE-03 - Chlorine electrode

• Atlas Scientific EZO-ORP - ORP sensor (indirect)

3. Spectrophotometer Method

• Use specific wavelength (530nm for DPD)

• More accurate than RGB

If You Must Use TCS34725

1. Use in controlled environment (dark box)

2. Always use same reagent amount

3. Calibrate frequently

4. Keep temperature constant

5. Use same test tubes

6. Filter water samples first

Would you like me to provide more details on:

• Building a proper test chamber?

• Implementing temperature compensation?

• Using electrochemical sensors instead?

• Creating a calibration curve?

The TCS34725 can work for this, but it's really meant for hobbyist/educational use rather than accurate water quality monitoring

FCL-01 Chlorine Sensor - Cost & Integration

Cost

The FCL-01 (and similar industrial chlorine sensors) typically cost:

• Sensor probe alone: $150-300

• With transmitter/controller: $400-800

• Complete kit: $500-1000+

These are industrial-grade sensors designed for pools/water treatment plants.

Integration Challenge

FCL-01 typically outputs:

• 4-20mA current loop (industrial standard)

• RS485 Modbus (some models)

• Not direct Arduino-friendly voltage

Converting 4-20mA to Arduino/ESP32

// Need a 250Ω resistor to convert 4-20mA to 1-5V

// 4mA = 1V = 0 ppm

// 20mA = 5V = max ppm (usually 10 or 20)

#define CHLORINE_PIN 34  // ESP32 ADC pin (or A0 for Arduino)

void setup() {

  Serial.begin(115200);

}

void loop() {

  int raw = analogRead(CHLORINE_PIN);

  // For ESP32 (12-bit ADC, 0-3.3V)

  float voltage = raw * (3.3 / 4095.0);

  // Convert voltage to mA (with 250Ω resistor)

  float current = voltage / 0.250;  // V = I*R

  // Convert mA to ppm (assuming 4-20mA = 0-10ppm)

  float ppm = ((current - 4.0) / 16.0) * 10.0;

  if (current < 3.5) {

    Serial.println("Sensor disconnected!");

  } else {

    Serial.print("Chlorine: ");

    Serial.print(ppm);

    Serial.println(" ppm");

  }

  delay(1000);

}

Required Interface Circuit

FCL-01 → [4-20mA Converter Module] → Arduino/ESP32

         (~$10-20 module)

Better Budget Alternatives for Makers

1. DFRobot Gravity Chlorine Sensor (~$60-80)

• Direct Arduino/ESP32 compatible

• 0-3.3V output

• Includes interface board

// DFRobot sensor - much simpler!

#define CL_PIN A0

void setup() {

  Serial.begin(9600);

}

void loop() {

  float voltage = analogRead(CL_PIN) * (5.0/1024.0);

  float ppm = voltage * 2.0;  // Simple linear conversion

  Serial.println(ppm);

  delay(1000);

}

2. Generic Chinese Chlorine Probes (~$30-50)

• Available on AliExpress/eBay

• Variable quality

• Usually 0-5V or 0-3.3V output

• Direct Arduino compatible

3. ORP Sensors (~$40-60)

• Measure oxidation potential (indirect chlorine)

• Atlas Scientific or DFRobot versions

• Easier to integrate

4. Pool/Spa Sensor Modules (~$80-120)

• Complete modules with display

• Often have analog output you can tap into

Recommendation for Hobbyists

Skip the industrial FCL-01 and go for:

1. Best Value: Generic chlorine probe + interface board (~$50 total)

2. Easiest: DFRobot Gravity Chlorine Sensor (~$70)

3. Budget: ORP sensor for indirect measurement (~$40)

Simple ESP32 Code for Generic Sensor

#define CHLORINE_PIN 34

#define SAMPLES 10

float readChlorine() {

  float sum = 0;

  for(int i = 0; i < SAMPLES; i++) {

    sum += analogRead(CHLORINE_PIN);

    delay(10);

  }

  float avg = sum / SAMPLES;

  float voltage = avg * (3.3 / 4095.0);

  return voltage * 3.0;  // Adjust multiplier based on calibration

}

The industrial FCL-01 is overkill for most Arduino/ESP32 projects - the cheaper alternatives work fine for hobbyist pool monitoring or water quality projects!

Search Terms for Affordable Chlorine Sensors for Charity Project

For Generic Chinese Chlorine Probes ($30-50)

Search on AliExpress/Alibaba/eBay:

• "residual chlorine sensor arduino"

• "CL2 sensor probe 0-5V"

• "free chlorine electrode probe"

• "water quality chlorine sensor module"

• "FCL chlorine probe analog output"

• "swimming pool chlorine sensor 4-20mA"

• "RS485 chlorine sensor modbus"

Specific model numbers to search:

• "CLE-03 chlorine electrode"

• "RCL-01 residual chlorine"

• "CS7820 chlorine sensor"

• "FCL502 chlorine probe"

For Pool/Spa Modules ($50-100)

Search terms:

• "pool tester ORP chlorine module"

• "swimming pool water quality sensor"

• "spa chlorine pH combo sensor"

• "pool automation sensor probe"

• "BLE-200 pool sensor" (specific model)

• "Hayward ORP sensor replacement"

Recommended Approach for Charity/Scalable Project

Option 1: ORP Sensor (Most Scalable) ~$15-25

Since you mentioned charity and scalability, ORP might be better:

Search for:

• "ORP probe arduino"

• "ORP-169 sensor module"

• "redox potential sensor"

• "ORP electrode BNC connector"

Why ORP for charity project:

• Much cheaper ($15 vs $50)

• More durable/longer lasting

• Correlates with chlorine (indirect but reliable)

• No expensive replacement membranes

Sample Arduino Code for ORP:

// ORP to Chlorine estimation

#define ORP_PIN A0

#define OFFSET 0  // Calibrate this

float getChlorineFromORP() {

  int raw = analogRead(ORP_PIN);

  float voltage = raw * 5.0 / 1024.0;

  int orpValue = (voltage * 1000) - 1500 + OFFSET; // Convert to mV

  // Rough correlation (pH dependent)

  // 650-750 mV = 0.5-1.0 ppm chlorine

  // 750-850 mV = 1.0-3.0 ppm chlorine

  float chlorinePPM;

  if (orpValue < 650) chlorinePPM = 0;

  else if (orpValue < 750) chlorinePPM = map(orpValue, 650, 750, 0.5, 1.0);

  else if (orpValue < 850) chlorinePPM = map(orpValue, 750, 850, 1.0, 3.0);

  else chlorinePPM = 3.0;

  return chlorinePPM;

}

Option 2: DIY Colorimetric (Ultra Low Cost) ~$10

For maximum scalability in developing regions:

Components:

• TCS34725 or any RGB sensor ($5)

• 3D printed test chamber

• DPD powder packets (bulk buy)

Search for:

• "DPD powder bulk 1000 packets"

• "pool test reagent DPD wholesale"

• "chlorine test powder sachets"

Recommended Full Build for Charity

// Low-cost chlorine tester for water safety

#include <Wire.h>

#include <LiquidCrystal_I2C.h>

#define ORP_PIN A0

#define BATTERY_PIN A1

#define LED_PIN 13

LiquidCrystal_I2C lcd(0x27, 16, 2);

void setup() {

  lcd.init();

  lcd.backlight();

  pinMode(LED_PIN, OUTPUT);

  lcd.setCursor(0,0);

  lcd.print("Water Chlorine");

  lcd.setCursor(0,1);

  lcd.print("Tester v1.0");

  delay(2000);

}

void loop() {

  float chlorine = readChlorineLevel();

  float battery = readBattery();

  lcd.clear();

  lcd.setCursor(0,0);

  lcd.print("Cl: ");

  lcd.print(chlorine, 1);

  lcd.print(" ppm");

  lcd.setCursor(0,1);

  if (chlorine < 0.5) {

    lcd.print("ADD CHLORINE!");

    digitalWrite(LED_PIN, HIGH);

  } else if (chlorine > 3.0) {

    lcd.print("TOO HIGH!");

    digitalWrite(LED_PIN, HIGH);

  } else {

    lcd.print("SAFE WATER");

    digitalWrite(LED_PIN, LOW);

  }

  delay(1000);

}

Bill of Materials (Scalable)

Version 1 - Ultra Budget ($15-20):

• Arduino Nano clone: $3

• ORP sensor probe: $12

• 16x2 LCD: $3

• Box + battery: $2

Version 2 - Better ($30-40):

• ESP32: $5

• Generic chlorine probe: $25

• OLED display: $5

• Rechargeable battery: $5

Where to Source in Bulk:

1. Direct from Manufacturers:
   
   

   • Search Alibaba for "chlorine sensor factory"

   • Minimum order: 10-50 units

   • Price drops to $10-15 per sensor

2. Specific Suppliers to Search:
   
   

   • "Kedida sensor" (Chinese manufacturer)

   • "Yosemitech water sensor"

   • "Kelilong electrode factory"

3. Alternative: Contact Pool Supply Wholesalers
   
   

   • They often have old/surplus sensors

   • Might donate for charity

Pro Tips for Charity Project:

1. Use phone app instead of LCD (cheaper):

// ESP32 with Bluetooth

#include <BluetoothSerial.h>

BluetoothSerial SerialBT;

void setup() {

  SerialBT.begin("WaterTester");

}

void loop() {

  float chlorine = readSensor();

  SerialBT.println(String(chlorine) + " ppm");

  delay(1000);

}

2. Consider test strips + camera for ultimate low cost

3. Partner with pool chemical companies for donated sensors

Would you like me to help you:

• Design a 3D printable enclosure?

• Create a phone app for the tester?

• Write a grant proposal for bulk sensor purchase?

• Find specific suppliers on Alibaba?