Automatic Hand Sanitizer Dispenser with IR Sensor and Low-Refill Alert using Arduino

Shared sanitizer pump bottles in college corridors, canteens and labs are pressed by hundreds of hands a day, which undermines the hygiene they are supposed to provide. Commercial automatic dispensers solve the touchless part but are priced for institutions, run on sealed proprietary refills, and give the owner no way to know the tank is empty until someone waves at a dead nozzle. This project builds the same idea the open student way: an Arduino Nano reads an FC-51 IR proximity sensor mounted under the nozzle and runs a mini submersible pump for a fixed few seconds per hand detection, while a 16x2 LCD reports READY, DISPENSING or REFILL NEEDED. An HC-SR04 ultrasonic sensor on the tank lid continuously measures the sanitizer surface, and when the level sinks below a set threshold the SIM800L GSM module sends a low-refill SMS to the owner's phone. Every module is standard and cheaply available, and the behaviour — sensor range, dispense time, alert threshold — is all adjustable in the firmware.

1. The FC-51 IR module emits infrared from its LED and watches for the reflection with its photodiode; the onboard LM393 comparator flips its digital output LOW when a hand enters the roughly 10 cm detection zone (potentiometer-adjusted, design target).
2. The Arduino Nano polls the IR output, and on a fresh detection it drives a 5 V relay module that switches the mini submersible pump (3–6 V DC, design target) for the configured dispense time — about 2 s by default, adjustable from 1–5 s in firmware.
3. Sanitizer travels from the pump at the tank bottom through silicone tubing to the downward nozzle on the stand; the pump stops when the timer expires, and a lockout of about 3 s (design target) ignores further triggers while a hand stays under the nozzle.
4. Independently, every few seconds the Arduino sends a 10 µs trigger pulse to the HC-SR04 on the tank lid, times the echo return, and converts it to the sanitizer surface distance (sensor range 2–400 cm, datasheet); averaging 5 readings smooths ripples into a stable fill percentage.
5. When the fill falls below the roughly 20% threshold (design target), the Nano issues AT commands over UART to the SIM800L (AT+CMGF=1, then AT+CMGS) to send the low-refill SMS to the stored owner number; the alert fires once per event and re-arms after the level rises past the threshold.
6. The 16x2 LCD mirrors the state machine throughout: READY on the first line with the fill percentage on the second, DISPENSING during a dispense, and blinking REFILL NEEDED when the level is low — so the unit is fully diagnosable without a computer attached.

Tech stack:

• Arduino Nano (ATmega328P, Arduino framework)
• FC-51 IR proximity sensor (LM393, adjustable 2–30 cm)
• HC-SR04 ultrasonic sensor (TRIG/ECHO, 40 kHz)
• SIM800L GSM module (quad-band 2G, AT commands, UART)
• Mini submersible DC pump · 5 V relay driver module
• 16x2 character LCD (I2C interface)
• LM2596 buck converter (dedicated 4.0 V GSM rail)
• Arduino IDE toolchain

• [Touchless IR-triggered dispensing] The FC-51 IR proximity sensor under the nozzle watches for a hand at roughly 10 cm (potentiometer-set, design target); on detection the Arduino switches the pump on through a relay module, so sanitizer flows with zero contact.
• [Ultrasonic tank-level monitoring] The HC-SR04 on the tank lid measures the distance to the sanitizer surface every few seconds and converts it to a fill percentage; the firmware averages several samples to smooth out surface ripples.
• [SMS low-refill alert] When the level drops below the firmware-set threshold (about 20% of tank depth, design target), the SIM800L sends a text-mode SMS to the owner's number; the alert fires once per empty event and re-arms only after a refill.
• [Live 16x2 LCD status] The display shows READY when idle, DISPENSING while the pump runs, and a blinking REFILL NEEDED when the level is low, so the unit's state is readable at a glance without a laptop.
• [Honest GSM power design] The SIM800L runs on its own 3.7–4.2 V rail from an LM2596 buck converter with 2 A peak capability, exactly as its hardware design requires — the Arduino's 5 V pin cannot supply it, and the build documents this as a deliberate design decision.
• [Firmware-configurable behaviour] Dispense time (1–5 s), level-alert threshold and the owner's phone number are constants at the top of the sketch, adjustable without touching any wiring.
• [Re-trigger lockout and alert cooldown] A short lockout after each dispense ignores further triggers while a hand lingers under the nozzle, and the SMS alert is rate-limited to one message per low-level event.

Configurable in firmware: dispense time, level threshold, owner number, lockout period. Optional add-on: piezo buzzer beep on each dispense. Not included (future scope): Wi-Fi/cloud dashboard, battery or solar power, multi-nozzle variants — quotable separately.

• Working automatic sanitizer dispenser prototype (tank, pump, nozzle stand, IR and ultrasonic sensors, SIM800L, LCD, Arduino Nano)
• Complete Arduino firmware source code (documented, configurable constants)
• Wiring diagram and full component list with sourcing notes
• Tank and stand assembly guide with silicone-tubing routing notes
• Calibration procedure: IR range potentiometer setting and level-threshold setup
• Project report PDF (background, sensor theory, methodology, results discussion)
• PPT presentation for final review
• Viva Q&A preparation document (IR sensing, ultrasonics, GSM AT commands, power design)