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Beginner

ANALOG / DISCRETE

< ₹500

3 – 6 Hours

IR Based Automatic Hand Sanitiser Dispenser

An automated touchless hand sanitiser dispenser built using an IR sensor module and a mini DC water pump.

Originally published by Rameshwer Prasad Nishad on ElectronicsForU

View original tutorial

How It Works

The IR Based Automatic Hand Sanitiser Dispenser operates as a touchless, automated fluid delivery system utilizing a discrete analog control circuit. At the heart of the detection stage is an IR sensor module built around an LM358 operational amplifier. This sensor continuously emits and monitors infrared light; when a user places their hand within the detection range, the reflected IR radiation alters the sensor's output state, generating a control signal. This low-power signal is routed to the base of a BC547 NPN bipolar junction transistor, which acts as an electronic switch. When the transistor's base receives sufficient voltage, it enters saturation, allowing current to flow from the 5V DC adapter through the coil of the 5V single-changeover relay. As the relay coil energizes, its mechanical switch changes state, completing the circuit for the mini submersible DC motor pump. The pump then activates, drawing liquid sanitizer from the attached plastic bottle and pushing it through the small plastic pipe to dispense a dose to the user's hands. To protect the discrete semiconductor components from voltage spikes generated by the inductive load of the relay coil, a 1N4007 flyback diode is placed in reverse bias across the relay terminals. Additionally, an LED indicator visually signals when the circuit is triggered. The entire system is assembled on a general-purpose PCB and powered reliably via the 5V DC adapter, providing a responsive and hygienic touch-free user experience without the need for microcontrollers or programmed software.

Why Build This

Design and deploy touchless hygiene infrastructure for engineering laboratories, academic offices, and shared campus facilities to minimize surface-borne pathogen transmission.

Gain practical undergraduate-level experience in integrating discrete analog sensors, transistor switching networks, and electromagnetic relays to control higher-power electromechanical loads.

Prototype a functional, standalone automation appliance on a general-purpose PCB using standard electronic components and readily available mechanical hardware.

Real-World Application

Touchless hygiene stations for public places, offices, hospitals, and homes to prevent germ transmission.

Skills You'll Learn

Transistor biasing and switching

Electromagnetic relay interfacing

Inductive load protection using flyback diodes

Analog sensor integration

DC motor pump control

Safety Precautions

Cover the IR module with suitable insulation and waterproofing material to protect it from liquid spills.

Technology Tags

IR SENSOR

BC547 TRANSISTOR

RELAY

DC SUBMERSIBLE PUMP

PCB ASSEMBLY

Frequently Asked Questions

Why is a 1N4007 diode included across the relay?

The 1N4007 acts as a flyback diode, safely dissipating the reverse voltage spike generated by the relay coil when it de-energizes, which protects the BC547 transistor from damage.

Can I adjust the detection distance of the IR sensor?

Yes, standard IR sensor modules typically feature an onboard potentiometer connected to the LM358 comparator, allowing you to fine-tune the sensitivity and effective detection range.

Do I need to write any code or program a microcontroller for this project?

No, this is a strictly hardware-based analog circuit controlled entirely by the state of the IR sensor module and transistor switch, requiring zero software.