AUTOMATIC HAND SANITIZER DISPENSER

1. Aim

To design and construct an automatic hand sanitizer dispenser using an infrared (IR) sensor and MOSFET-based switching to operate a water pump.

2. Components Used

S.N

Component

Purpose

1

Infrared LED (IR Emitter)

Emits invisible IR light toward the detection area

2

Photodiode (IR Receiver)

Receives reflected IR light when an object is present

3

IRFZ44N MOSFET

Acts as an electronic switch to control the pump

4

Water Pump (3–6V)

Dispenses sanitizer liquid

5

Resistors (R1, R2, R3)

R1 → limits IR LED current
R2 → reverse bias for photodiode
R3 → noise control, pulls signal to ground

6

3.7V Lithium-ion Battery

Power supply for the entire circuit

3. Circuit Description

 

➤ IR Emitter & Receiver Section

  • IR LED emits continuous infrared light.
  • Photodiode is reverse biased so normally it does not conduct.
  • When no object is present, the photodiode receives very little light → voltage at point P stays low due to a 20kΩ resistor to ground.

➤ Detection of a Hand

  • When a hand or object is placed in front of the sensor:
    • IR light reflects back to the photodiode.
    • Photodiode starts to conduct more current.
    • Voltage at point P increases (suitable threshold level reached).

➤ MOSFET Switching

  • When the voltage at P becomes high:
    • Gate of IRFZ44N receives enough voltage.
    • MOSFET turns ON.
    • Water pump gets direct power and starts pumping sanitizer.
  • When the hand is removed:
    • Signal at P drops.
    • MOSFET turns OFF.
    • Pump stops.

4. Working Mechanism

  1. When power is applied:
    • IR LED turns ON.
    • Photodiode stays inactive (reverse-biased).
    • MOSFET remains OFF and pump is OFF.
  2. When a hand/object comes in front:
    • IR light reflects to the photodiode.
    • Photodiode conducts → creates voltage at point P.
    • If voltage is strong enough:
      • MOSFET is triggered.
      • Pump turns ON → sanitizer is dispensed.
  3. When the hand/object is removed:
    • No reflection → photodiode stop conducting.
    • Voltage at P drops → MOSFET OFF.
    • Pump stops.

5. Circuit Operation Conclusion

“When power is ON, the IR LED emits infrared rays and the photodiode remains ready.
When an obstacle (hand) appears, the photodiode receives the reflected IR light and starts conducting.
This generates a suitable signal at point P which turns ON the MOSFET.
As a result, the water pump operates and sanitizer is dispensed.”

6. Applications

  • Touchless hand sanitizer machine
  • Automatic water dispenser
  • Contactless soap dispenser
  • COVID-prevention hygiene stations

7. Advantages

  • No physical touch → prevents contamination
  • Low power consumption
  • Simple and cost-effective circuit
  • Fast response time

8. Precautions

  • Protect battery from over-discharge
  • Avoid high current draw through IR LED
  • Seal pump connections to prevent leakage

9. Result

The designed automatic hand sanitizer system successfully detects a hand using IR sensing and activates the pump using a MOSFET switch. The system operates efficiently on a 3.7V battery and provides touchless sanitization.

 

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