Arduino Hands-On Programming and Robotics Course

📘 MODULE 7 – Automatic Water Dispenser

Lesson 7.2 – IR Sensor + Pump Circuit

Learning Objectives

By the end of this lesson, students will be able to:

Understand the complete circuit of the Automatic Water Dispenser.
Learn how the IR sensor, relay module, and water pump are connected.
Identify the purpose of each circuit connection.
Understand signal flow from sensor detection to pump activation.
Build the circuit safely on a breadboard.
Verify all wiring before testing.
Troubleshoot common circuit connection mistakes.

Main Content

Introduction

In the previous lesson, we learned about the Automatic Water Dispenser project and its working principle.

Now it is time to build the actual hardware circuit.

The circuit consists of four main components:

Arduino UNO
IR Sensor Module
Relay Module
Mini DC Water Pump

These components work together to create a touchless water dispensing system.

Project Circuit Overview

The system works in the following sequence:

Hand/Bottle Detected

        ↓

IR Sensor

        ↓

Arduino UNO

        ↓

Relay Module

        ↓

Water Pump

        ↓

Water Dispensing

The IR sensor acts as the input device.

The relay and pump act as the output system.

Arduino processes the input and controls the output.

Components Required

Component	Quantity
Arduino UNO	1
IR Sensor Module	1
Single Channel Relay Module	1
Mini DC Water Pump	1
Breadboard	1
Jumper Wires	Several
USB Cable	1
External 5V–12V Supply (Pump)	1

Understanding Circuit Sections

The complete circuit can be divided into three sections:

Section 1: IR Sensor Connections

Used for object detection.

Section 2: Relay Connections

Used for switching the pump.

Section 3: Pump Connections

Used for dispensing water.

IR Sensor Connections

A typical IR sensor module contains:

VCC
GND
OUT

IR Sensor → Arduino Connections

IR Sensor Pin	Arduino Pin
VCC	5V
GND	GND
OUT	D2

VCC Connection

IR VCC → Arduino 5V

Provides power to the sensor.

GND Connection

IR GND → Arduino GND

Completes the electrical circuit.

OUT Connection

IR OUT → Arduino D2

Sends detection signals to Arduino.

When an object is detected:

OUT = LOW or HIGH

depending on sensor type and adjustment.

Relay Module Connections

A relay module usually contains:

VCC
GND
IN

Relay → Arduino Connections

Relay Pin	Arduino Pin
VCC	5V
GND	GND
IN	D8

Relay VCC

Relay VCC → Arduino 5V

Powers the relay module.

Relay GND

Relay GND → Arduino GND

Provides ground reference.

Relay IN

Relay IN → Arduino D8

Arduino controls the relay through this pin.

Water Pump Connections

The pump should NOT be powered directly from an Arduino digital pin.

Reason:

Pump Current > Arduino Pin Current Capacity

Doing so may damage the Arduino.

Instead, use the relay.

Relay Output Terminals

Most relay modules provide:

COM
NO
NC

Recommended Connection

Use:

COM
NO

terminals.

This ensures:

Pump OFF when Relay OFF
Pump ON when Relay ON

Pump Wiring Diagram

Power Supply (+)

        |

        |

       COM

        |

       NO

        |

        |

     Pump (+)

Pump (-)

        |

Power Supply (-)

Working of Relay Circuit

When Arduino sends:

HIGH

(or LOW depending on module type)

Relay activates.

Then:

COM ↔ NO Connected

Current flows to the pump.

The pump starts.

When Arduino turns relay OFF:

COM ↔ NO Disconnected

Current stops.

The pump stops.

Complete Circuit Table

IR Sensor

Sensor Pin	Arduino
VCC	5V
GND	GND
OUT	D2

Relay Module

Relay Pin	Arduino
VCC	5V
GND	GND
IN	D8

Pump

Pump Connection	Connected To
Positive	Relay NO
Negative	Power Supply Negative

Breadboard Layout Tips

Place components in an organized manner.

Example:

IR Sensor

      |

Arduino ---- Relay

      |

    Pump

Keep wiring short and neat.

This reduces troubleshooting problems.

Signal Flow Through Circuit

The complete signal flow is:

Hand Detected

      ↓

IR Sensor

      ↓

Arduino D2

      ↓

Arduino Program

      ↓

Arduino D8

      ↓

Relay Module

      ↓

Pump Power

      ↓

Water Flow

Understanding this flow helps identify problems quickly.

Power Supply Considerations

The relay and sensor can usually operate from Arduino 5V.

However, the pump may require:

5V
6V
9V
12V

depending on the model.

Always check the pump specifications.

Why Use an External Power Supply?

Example:

Pump Current Requirement:

500mA

Arduino USB current:

Limited

The pump may:

Run slowly
Restart Arduino
Cause unstable operation

Therefore external power is recommended.

Circuit Verification Checklist

Before powering the circuit:

✅ IR Sensor VCC connected to 5V

✅ IR Sensor GND connected to GND

✅ IR Sensor OUT connected to D2

✅ Relay VCC connected to 5V

✅ Relay GND connected to GND

✅ Relay IN connected to D8

✅ Pump connected through relay terminals

✅ External power supply connected properly

✅ No loose wires

Common Wiring Mistakes

Mistake 1: Reversing VCC and GND

Wrong:

VCC → GND
GND → 5V

This may damage the module.

Mistake 2: Connecting Pump Directly to Arduino Pin

Wrong:

Arduino Pin → Pump

Can damage Arduino.

Mistake 3: Using NC Instead of NO

If connected to NC:

Pump ON by default

which may not be desired.

Mistake 4: Missing Common Ground

All modules should share the same ground reference.

Testing Connections Without Water

Before adding water:

Build the circuit.
Upload test code.
Place hand near sensor.
Listen for relay click.
Observe pump operation.

Testing without water helps prevent spills during troubleshooting.

Real-World Example

Imagine a water bottle placed near the dispenser.

Process:

Bottle Near Sensor

        ↓

Sensor Detects Bottle

        ↓

Arduino Receives Signal

        ↓

Relay Activates

        ↓

Pump Starts

        ↓

Water Dispensed

When the bottle is removed:

Bottle Removed

        ↓

Sensor Clears

        ↓

Relay OFF

        ↓

Pump Stops

Best Practices

Keep Electronics Away from Water

Protect Arduino and relay from splashes.

Use Proper Pump Voltage

Match pump voltage with power supply.

Double-Check Wiring

Verify all connections before powering.

Secure Components

Prevent accidental wire disconnections.

Test Components Individually

Verify sensor and relay operation before connecting the pump.

Summary

The Automatic Water Dispenser circuit consists of an IR sensor, Arduino UNO, relay module, and water pump. The IR sensor detects a hand or bottle and sends a signal to Arduino. Arduino processes the signal and activates the relay. The relay then supplies power to the water pump, allowing water to flow. Proper wiring and power management are essential for safe and reliable operation.

Key Terms

IR Sensor
Relay Module
Water Pump
COM Terminal
NO Terminal
Arduino UNO
Input Signal
Output Control
External Power Supply
Automation Circuit

Quiz

1. Which Arduino pin receives the IR sensor signal in this lesson?

A. D8

B. D13

C. D2

D. A0

Answer: C

2. Which Arduino pin controls the relay?

A. D8

B. D2

C. A1

D. D12

Answer: A

3. Why should the pump not be connected directly to Arduino?

A. Pump is too small

B. Arduino cannot provide sufficient current

C. Pump requires Wi-Fi

D. Arduino cannot read pumps

Answer: B

4. Which relay terminal is commonly used to keep the pump OFF until activation?

A. NC

B. COM

C. NO

D. GND

Answer: C

5. What is the purpose of the relay module?

A. Measure distance

B. Detect objects

C. Switch pump power safely

D. Store data

Answer: C

Assignment

Practical Activity

Build the complete Automatic Water Dispenser circuit on a breadboard.

Perform the following:

Connect the IR sensor.
Connect the relay module.
Connect the water pump through the relay.
Verify all wiring using the checklist.
Draw the complete circuit diagram in your notebook.

Answer the following:

Why is a relay necessary?
Why is an external power source recommended for the pump?
What happens when the sensor detects a bottle?