Hardware Wiring & Connections

System Overview

The Aqua-IoT hardware system consists of three main components:

Arduino - Sensor interface and data collection
Raspberry Pi - MQTT bridge and network gateway
Sensors - Environmental and water quality monitoring

Complete Pin Connection Map

Arduino Uno Pin Assignments

Based on sensores.ino configuration:

Component	Arduino Pin	Pin Type	Notes
DHT11 Data	Digital 2	Digital I/O	Temperature & humidity sensor
HC-SR04 Echo	Digital 4	Digital Input	Ultrasonic distance sensor
HC-SR04 Trigger	Digital 6	Digital Output	Ultrasonic distance sensor
DS18B20 Data	Digital 10	OneWire	Waterproof temperature sensor
LDR Signal	Analog A0	Analog Input	Light-dependent resistor
TDS Sensor	Analog A4	Analog Input	Water quality sensor
5V Power	5V	Power	Power supply for all sensors
Ground	GND	Ground	Common ground (multiple GND pins available)

Arduino Uno has limited 5V current output (~400mA). If powering multiple sensors, consider using an external 5V power supply.

Detailed Sensor Wiring

DHT11 - Temperature & Humidity Sensor

Pin Configuration: DHTPIN 2 (sensores.ino:16)

DHT11          Arduino
─────────      ────────
VCC   ────────  5V
DATA  ────────  Digital Pin 2
NC    ────────  (Not Connected)
GND   ────────  GND

Wiring Notes:

Use 3-pin or 4-pin DHT11 module
Built-in modules often include pull-up resistor
If using bare sensor, add 10kΩ pull-up resistor between VCC and DATA

DHT11 requires stable 5V power. Voltage drops can cause reading errors. Keep sensor wires under 20cm if possible.

DS18B20 - Waterproof Temperature Sensor

Pin Configuration: DS18B20 10 (sensores.ino:17)

DS18B20        Arduino
─────────      ────────
Red (VCC)  ──  5V
Yellow (DATA)  Digital Pin 10
Black (GND) ── GND

Required: 4.7kΩ pull-up resistor between DATA (Yellow) and VCC (Red)

        4.7kΩ
5V ──────/\/\/\───┬─── Digital Pin 10
                   │
                 (Yellow)

Wiring Notes:

OneWire protocol requires pull-up resistor
Waterproof probe version has 3 wires
Can use parasitic power mode (2-wire) but 3-wire is more reliable
Suitable for aquarium water temperature monitoring

Gravity TDS - Total Dissolved Solids Sensor

Pin Configuration: TdsSensorPin A4 (sensores.ino:18)

TDS Sensor     Arduino
───────────    ────────
VCC   ────────  5V
GND   ────────  GND
A     ────────  Analog Pin A4

Configuration Parameters (sensores.ino:51-55):

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

Wiring Notes:

Probe must be fully submerged in water
Keep probe clean for accurate readings
Temperature compensation is applied using media = 25 (25°C average)
Outputs PPM (parts per million) for water quality

TDS sensor requires calibration. Use EEPROM to store calibration values for consistent readings across power cycles.

HC-SR04 - Ultrasonic Distance Sensor

Pin Configuration: echo=4, trigger=6 (sensores.ino:19-20)

HC-SR04        Arduino
─────────      ────────
VCC   ────────  5V
TRIG  ────────  Digital Pin 6
ECHO  ────────  Digital Pin 4
GND   ────────  GND

Distance Calculation (sensores.ino:127-139):

void calculo() {
  digitalWrite(trigger, LOW);
  delayMicroseconds(2);
  digitalWrite(trigger, HIGH);
  delayMicroseconds(10);
  digitalWrite(trigger, LOW);
  
  tempo = pulseIn(echo, HIGH);
  // Distance = (time × speed of sound) / 2
  distancia = float(tempo * 0.0343) / 2;
  delay(10);
}

Wiring Notes:

Measures distance: 2cm to 400cm
Used for water level monitoring
Mount sensor above water surface pointing downward
Speed of sound constant: 0.0343 cm/µs at 20°C
Returns distance in centimeters

LDR - Light Dependent Resistor

Pin Configuration: sensorPin = A0 (ldr.ino:9) Voltage Divider Circuit:

5V ───┬─── 10kΩ Resistor ───┬─── GND
      │                      │
      └─── LDR Sensor ───────┤
                              │
                              └─── Analog Pin A0

Circuit Configuration (ldr.ino:2-6):

#define VIN 5      // Operating voltage
#define R 10000    // 10kΩ fixed resistor

Conversion Formula (ldr.ino:32-40):

int sensorRawToPhys(int raw) {
  // Analog to voltage
  float Vout = float(raw) * (VIN / float(1024));
  
  // Voltage to resistance
  float RLDR = (R * (VIN - Vout)) / Vout;
  
  // Resistance to lumen
  int phys = 500 / (RLDR / 1000);
  return phys;
}

Wiring Notes:

10kΩ fixed resistor creates voltage divider
Output range: 0-1023 (10-bit ADC)
Converts to lumen for light intensity measurement
Used for plant environment monitoring

LDR polarity doesn’t matter, but ensure the 10kΩ resistor is connected between LDR and GND for proper voltage divider operation.

Arduino Power Considerations

Current Requirements

Component	Current Draw	Notes
DHT11	1-2 mA	Low power
DS18B20	1-1.5 mA	Low power
HC-SR04	15 mA	During pulse
TDS Sensor	5-20 mA	Variable
LDR Circuit	<1 mA	Minimal
Total	~25-40 mA	Safe for USB power

Power Options:

USB Power (Recommended for development)
- 5V from USB port (computer or wall adapter)
- Current limit: ~500 mA
- Sufficient for all sensors
External Power Supply
- Use DC barrel jack (7-12V input)
- Arduino regulates to 5V
- Required for deployment without computer
Separate Sensor Power (For reliability)
- External 5V power supply for sensors
- Connect Arduino and sensor GND together
- Prevents voltage drops during sensor operation

Raspberry Pi Connection

USB Serial Connection

Configuration: /dev/ttyACM0 at 9600 baud (mqtt-arduino.py:27)

Arduino USB Port  ───── USB Cable ─────  Raspberry Pi USB Port

Serial Parameters:

ser = serial.Serial('/dev/ttyACM0', 9600, timeout=1)

Parameter	Value	Notes
Port	`/dev/ttyACM0`	Auto-assigned by Linux
Baud Rate	9600	Must match Arduino: `Serial.begin(9600)`
Timeout	1 second	Read timeout for `ser.readline()`
Data Bits	8	Default
Parity	None	Default
Stop Bits	1	Default

The USB connection provides both data communication and power to the Arduino. For production, use external power for Arduino.

Network Architecture

Raspberry Pi Network Setup

┌─────────────────────────────────────────┐
│         Raspberry Pi                     │
│  ┌─────────────────────────────────┐   │
│  │  Python: mqtt-arduino.py        │   │
│  │  (USB Serial Reader & Publisher)│   │
│  └─────────────────────────────────┘   │
│              ↓                           │
│  ┌─────────────────────────────────┐   │
│  │  Mosquitto MQTT Broker          │   │
│  │  Port: 18083                    │   │
│  └─────────────────────────────────┘   │
│              ↓                           │
│  ┌─────────────────────────────────┐   │
│  │  Python: mqtt-django.py         │   │
│  │  (MQTT Subscriber & API Client) │   │
│  └─────────────────────────────────┘   │
│              ↓                           │
│      Network Connection                 │
│      (WiFi/Ethernet)                    │
└─────────────────────────────────────────┘
              ↓ HTTP POST
    ┌─────────────────────┐
    │  Django REST API    │
    │  Port: 8000         │
    └─────────────────────┘

Assembly Instructions

Prepare Arduino

Install Arduino IDE and required libraries:
- DHT sensor library
- OneWire
- DallasTemperature
- GravityTDS
Upload sensores.ino to Arduino board

Test serial output:

# Arduino IDE: Tools > Serial Monitor (9600 baud)

Connect DHT11 sensor

Connect VCC to Arduino 5V
Connect DATA to Digital Pin 2
Connect GND to Arduino GND
If using bare sensor, add 10kΩ pull-up resistor

Connect DS18B20 sensor

Connect Red wire to Arduino 5V
Connect Yellow wire to Digital Pin 10
Connect Black wire to Arduino GND
Critical: Add 4.7kΩ pull-up resistor between Yellow and Red wires

Connect TDS sensor

Connect sensor VCC to Arduino 5V
Connect sensor signal to Analog Pin A4
Connect sensor GND to Arduino GND
Submerge probe in water for testing

Connect HC-SR04 sensor

Connect VCC to Arduino 5V
Connect TRIG to Digital Pin 6
Connect ECHO to Digital Pin 4
Connect GND to Arduino GND
Position sensor above water surface

Connect LDR sensor

Build voltage divider:
- Connect 5V to one leg of LDR
- Connect other leg of LDR to Analog Pin A0
- Connect 10kΩ resistor from A0 to GND
Position in plant area to measure light

Connect to Raspberry Pi

Connect Arduino USB port to Raspberry Pi USB port
Verify connection:
```
ls /dev/ttyACM*
```
Set permissions:
```
sudo chmod 666 /dev/ttyACM0
```

Test complete system

Power on Arduino (via USB)
Run Raspberry Pi bridge:
```
python3 mqtt-arduino.py
```

Monitor MQTT messages:

mosquitto_sub -h localhost -p 18083 -t "sensores/#" -v

Safety & Best Practices

Electrical Safety

Water and Electronics:

Keep Arduino and Raspberry Pi away from water
Only DS18B20 and TDS probes should contact water
Use waterproof enclosures for long-term deployment
Ensure all connections are secure and insulated

Cable Management

Use appropriate wire gauge (22-24 AWG for sensors)
Keep sensor wires under 1 meter when possible
Label all connections for easy maintenance
Use different colored wires:
- Red: 5V/VCC
- Black: GND
- Yellow/Green: Signal/Data

Grounding

Critical: Connect all GND pins to common ground
Arduino and sensors must share the same GND reference
If using external power supply, connect GND to Arduino GND

Mounting

Mount Arduino in dry, ventilated enclosure
Position DHT11 away from heat sources
Mount HC-SR04 perpendicular to water surface
Secure TDS and DS18B20 probes in water flow area
Position LDR in representative location for plant light

Troubleshooting

No Serial Data from Arduino

Check USB connection: ls /dev/ttyACM*
Verify baud rate: 9600 in both Arduino and Python
Test with Arduino Serial Monitor first
Check serial permissions: sudo chmod 666 /dev/ttyACM0

Sensor Reading Errors

DHT11 returns NaN:

Check power connection
Verify pin connection to Digital 2
Add/check 10kΩ pull-up resistor

DS18B20 returns -127°C:

Add 4.7kΩ pull-up resistor (most common issue)
Check OneWire connection to Pin 10
Verify sensor is not damaged

TDS reads 0 or very high:

Ensure probe is fully submerged
Clean probe contacts
Calibrate sensor
Check connection to A4

HC-SR04 returns 0 or timeout:

Verify Trigger on Pin 6, Echo on Pin 4
Check if sensor is within range (2-400cm)
Ensure no angled or sound-absorbing surfaces nearby

LDR returns constant value:

Check voltage divider circuit
Verify 10kΩ resistor value
Test in different lighting conditions
Check connection to A0

Power Issues

Brownout/Reset: Use external 5V supply for sensors
Unstable readings: Add 100µF capacitor across 5V and GND
USB not detected: Try different USB cable or port

Reference Diagrams

For visual wiring diagrams, refer to:

Arduino Uno pinout: https://docs.arduino.cc/hardware/uno-rev3
Individual sensor datasheets for specific wiring

Next Steps

Arduino Sensors

Configure Arduino sensor code

Raspberry Pi Bridge

Set up MQTT bridge software

Get Started

Hardware Setup

Web Dashboard

Deployment

Hardware Wiring & Connections

System Overview

Complete Pin Connection Map

Arduino Uno Pin Assignments

Detailed Sensor Wiring

DHT11 - Temperature & Humidity Sensor

DS18B20 - Waterproof Temperature Sensor

Gravity TDS - Total Dissolved Solids Sensor

HC-SR04 - Ultrasonic Distance Sensor

LDR - Light Dependent Resistor

Arduino Power Considerations

Current Requirements

Raspberry Pi Connection

USB Serial Connection

Network Architecture

Raspberry Pi Network Setup

Assembly Instructions

Safety & Best Practices

Electrical Safety

Cable Management

Grounding

Mounting

Troubleshooting

No Serial Data from Arduino

Sensor Reading Errors

Power Issues

Reference Diagrams

Next Steps

Arduino Sensors

Raspberry Pi Bridge

Build docs developers (and LLMs) love

Get Started

Hardware Setup

Web Dashboard

Deployment

​System Overview

​Complete Pin Connection Map

​Arduino Uno Pin Assignments

​Detailed Sensor Wiring

​DHT11 - Temperature & Humidity Sensor

​DS18B20 - Waterproof Temperature Sensor

​Gravity TDS - Total Dissolved Solids Sensor

​HC-SR04 - Ultrasonic Distance Sensor

​LDR - Light Dependent Resistor

​Arduino Power Considerations

​Current Requirements

​Raspberry Pi Connection

​USB Serial Connection

​Network Architecture

​Raspberry Pi Network Setup

​Assembly Instructions

​Safety & Best Practices

​Electrical Safety

​Cable Management

​Grounding

​Mounting

​Troubleshooting

​No Serial Data from Arduino

​Sensor Reading Errors

​Power Issues

​Reference Diagrams

​Next Steps

Arduino Sensors

Raspberry Pi Bridge

Build docs developers (and LLMs) love

System Overview

Complete Pin Connection Map

Arduino Uno Pin Assignments

Detailed Sensor Wiring

DHT11 - Temperature & Humidity Sensor

DS18B20 - Waterproof Temperature Sensor

Gravity TDS - Total Dissolved Solids Sensor

HC-SR04 - Ultrasonic Distance Sensor

LDR - Light Dependent Resistor

Arduino Power Considerations

Current Requirements

Raspberry Pi Connection

USB Serial Connection

Network Architecture

Raspberry Pi Network Setup

Assembly Instructions

Safety & Best Practices

Electrical Safety

Cable Management

Grounding

Mounting

Troubleshooting

No Serial Data from Arduino

Sensor Reading Errors

Power Issues

Reference Diagrams

Next Steps