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Overview

The Aqua-IoT system uses an Arduino board with multiple sensors to monitor environmental conditions for both aquarium and plant areas. The main sensor configuration is located in sensores.ino which integrates all sensor readings into a single monitoring system.

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Hardware Components

The system uses the following sensors:
  • DHT11 - Temperature and humidity sensor for plant environment
  • DS18B20 - Waterproof temperature sensor for aquarium water
  • Gravity TDS - Total Dissolved Solids sensor for water quality
  • HC-SR04 - Ultrasonic sensor for water level monitoring
  • LDR (Photoresistor) - Light intensity sensor for plant monitoring

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Required Libraries

Install these libraries through the Arduino IDE Library Manager: 
#include "DHT.h"              // DHT sensor library
#include <OneWire.h>           // OneWire protocol for DS18B20
#include <DallasTemperature.h> // DS18B20 temperature sensor
#include <EEPROM.h>            // EEPROM for TDS calibration
#include "GravityTDS.h"        // Gravity TDS sensor library

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Pin Configuration

The following pins are used in the complete sensor setup:
SensorPinTypePurpose
DHT112DigitalTemperature & humidity (plants)
HC-SR04 Echo4DigitalUltrasonic distance (water level)
HC-SR04 Trigger6DigitalUltrasonic trigger (water level)
DS18B2010Digital (OneWire)Water temperature
LDRA0AnalogLight intensity
TDS SensorA4AnalogWater quality (TDS)
All sensors operate at 5V. Ensure your Arduino board provides stable 5V output for accurate readings.

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Complete Sensor Setup

1

Define sensor constants

Configure the pin assignments and sensor parameters:
// DHT11 Configuration
#define DHTPIN 2
#define DHTTYPE DHT11

// DS18B20 Water Temperature
#define DS18B20 10

// TDS Sensor
#define TdsSensorPin A4

// HC-SR04 Ultrasonic
const int echo = 4;
const int trigger = 6;

// LDR Configuration
const int sensorPin = A0;
#define VIN 5          // Operating voltage
#define R 10000        // 10K resistor value
#define DELAY 500      // Reading delay
2

Initialize sensor objects

Create instances of sensor libraries:
// Initialize DHT11
DHT dht(DHTPIN, DHTTYPE);

// Initialize DS18B20
OneWire ourWire(DS18B20);
DallasTemperature sensors(&ourWire);

// Initialize TDS Sensor
GravityTDS gravityTds;
float media = 25;  // Average temperature for TDS compensation
float tdsValue = 0;

// HC-SR04 Variables
long tempo;
float distancia;

// LDR Variables
int sensorVal;
int lux;
3

Configure setup() function

Initialize serial communication and configure all sensors:
void setup() {
  Serial.begin(9600);
  Serial.println(F("Sensor Ativado"));

  // Start DHT11
  dht.begin();

  // Start DS18B20
  sensors.begin();

  // Configure TDS Sensor
  gravityTds.setPin(TdsSensorPin);
  gravityTds.setAref(5.0);      // 5V reference voltage
  gravityTds.setAdcRange(1024); // 10-bit ADC
  gravityTds.begin();

  // Configure HC-SR04
  pinMode(echo, INPUT);
  pinMode(trigger, OUTPUT);
  
  delay(100);
}
4

Implement sensor reading loop

Read all sensors and output data via serial:
void loop() {
  delay(2000);  // 2-second reading interval

  // Read DHT11 (Temperature & Humidity)
  float h = dht.readHumidity();
  float t = dht.readTemperature();
  float f = dht.readTemperature(true);

  if (isnan(h) || isnan(t) || isnan(f)) {
    Serial.println(F("Erro na leitura do sensor"));
    return;
  }

  Serial.print(F("Umidade: "));
  Serial.print(h);
  Serial.print(F("%  Temperatura: "));
  Serial.print(t);
  Serial.print(F("°C "));
  Serial.print(f);
  Serial.println(F("°F"));

  // Read DS18B20 (Water Temperature)
  sensors.requestTemperatures();
  Serial.print("Temperatura: ");
  Serial.print(sensors.getTempCByIndex(0));
  Serial.println("°C");

  // Read TDS Sensor
  gravityTds.setTemperature(media);
  gravityTds.update();
  tdsValue = gravityTds.getTdsValue();
  Serial.print(tdsValue, 0);
  Serial.println("ppm");

  // Read HC-SR04 (Water Level)
  calculo();
  Serial.print("Distância: ");
  Serial.print(distancia);
  Serial.print("cm");
  Serial.println();

  // Read LDR (Light Intensity)
  sensorVal = analogRead(sensorPin);
  lux = sensorRawToPhys(sensorVal);
  Serial.print(F("O valor do sensor é = "));
  Serial.println(sensorVal);
  Serial.print(F("O valor físico é = "));
  Serial.print(lux);
  Serial.println(F(" lumen"));
  delay(DELAY);
}

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Sensor-Specific Functions

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HC-SR04 Distance Calculation

The ultrasonic sensor measures water level by calculating distance: 
void calculo() {
  digitalWrite(trigger, LOW);
  delayMicroseconds(2);
  digitalWrite(trigger, HIGH);
  delayMicroseconds(10);
  digitalWrite(trigger, LOW);
  
  tempo = pulseIn(echo, HIGH);
  // Distance formula: (time * speed of sound) / 2
  distancia = float(tempo * 0.0343) / 2;
  delay(10);
}

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LDR Lux Conversion

Convert LDR analog reading to physical lux value: 
int sensorRawToPhys(int raw) {
  // Convert analog to voltage
  float Vout = float(raw) * (VIN / float(1024));
  
  // Convert voltage to resistance
  float RLDR = (R * (VIN - Vout)) / Vout;
  
  // Convert resistance to lumen
  int phys = 500 / (RLDR / 1000);
  return phys;
}

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Serial Communication Settings

The serial baud rate is set to 9600 bps. Ensure your Raspberry Pi bridge uses the same baud rate for proper communication.
Serial output format: 
Sensor Ativado
Umidade: 65.00%  Temperatura: 24.00°C 75.20°F
Temperatura: 23.50°C
450ppm
Distância: 12.5cm
O valor do sensor é = 512
O valor físico é = 30 lumen

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Individual Sensor Examples

For testing individual sensors, refer to the standalone files:
  • DHT11 only: ~/workspace/source/Arduino/temperatura-umidade.ino
  • DS18B20 only: ~/workspace/source/Arduino/temperatura-agua.ino
  • TDS only: ~/workspace/source/Arduino/tds.ino
  • LDR only: ~/workspace/source/Arduino/ldr.ino
  • HC-SR04 only: ~/workspace/source/Arduino/nivel-agua.ino

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Troubleshooting

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DHT11 Reading Errors

If you see “Erro na leitura do sensor”:
  • Check 5V power connection
  • Verify pin connection to Digital Pin 2
  • Ensure 2-second delay between readings
  • Check DHT library installation

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DS18B20 Returns -127°C

  • Verify OneWire connection on Pin 10
  • Add 4.7K pull-up resistor between data line and VCC
  • Check sensor polarity (GND, Data, VCC)

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TDS Sensor Unstable Readings

  • Calibrate sensor using gravityTds.begin()
  • Ensure probe is fully submerged
  • Use temperature compensation (default 25°C)
  • Clean probe contacts regularly

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HC-SR04 Distance Errors

  • Keep sensor away from angled surfaces
  • Ensure trigger (Pin 6) and echo (Pin 4) are correctly connected
  • Maximum range: ~4 meters
  • Minimum range: ~2 cm

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LDR Returns 0 or Maximum

  • Check 10K resistor connection
  • Verify analog pin A0 connection
  • Test with different lighting conditions
  • Ensure proper voltage divider circuit

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Next Steps

Raspberry Pi Bridge

Set up the MQTT bridge to receive sensor data

Wiring Diagram

View complete hardware wiring connections

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