Practical 4

Touchless Hand Sanitizer Dispenser

Contact-free dispensing with a fixed pump time

Aim

To dispense a fixed quantity of sanitizer automatically when a hand is detected, without the user touching the dispenser.

Overview

An IR obstacle sensor (or ultrasonic sensor) detects when a hand is placed under the nozzle. On detection, the Arduino activates a small DC pump through a transistor/relay for a fixed duration (e.g. 2 seconds) and then locks out for a short idle time so one hand motion produces exactly one dose. A status LED shows when the pump is running.

Components Required

Arduino Uno
IR obstacle avoidance sensor module (or HC-SR04)
5V DC peristaltic pump
NPN transistor (TIP120/2N2222) or relay module + flyback diode
Green LED + 220 ohm resistor (pump indicator)
Breadboard and jumper wires

Circuit Connections

From	To	Note
IR sensor VCC	Arduino 5V	-
IR sensor GND	Arduino GND	-
IR sensor OUT	Arduino D2	LOW when an object is detected (most modules)
Transistor base (via 1k)	Arduino D8	Switches the pump
Pump +	External 5V	-
Pump -	Transistor collector, emitter to GND	-
LED anode (via 220R)	Arduino D9	-
LED cathode	Arduino GND	-

Interactive Circuit Diagram

Simulate the circuit: adjust the sensor inputs below and watch the outputs react according to the control logic.

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Working

The Arduino continuously polls the IR sensor output.
When a hand is detected and the system is idle, the pump is switched ON.
The pump stays ON for PUMP_TIME (fixed dose time).
After dispensing, a LOCKOUT time ignores new detections so one hand motion gives one dose.
The indicator LED is ON exactly while the pump runs.

Control Logic

IF (hand detected) AND (state == IDLE): run pump for PUMP_TIME, then enter LOCKOUT for 1 s. The lockout prevents repeated dosing when the hand lingers under the sensor.

Arduino Code

1// Practical 4: Touchless Hand Sanitizer Dispenser
2const int IR_PIN     = 2;   // IR sensor output (LOW = hand detected)
3const int PUMP_PIN   = 8;   // Transistor / relay driving the pump
4const int LED_PIN    = 9;   // Pump status LED
5
6const unsigned long PUMP_TIME  = 2000;  // ms - fixed dose duration
7const unsigned long LOCKOUT    = 1000;  // ms - ignore hands after dosing
8
9enum State { IDLE, DISPENSING, WAIT };
10State state = IDLE;
11unsigned long stateStart = 0;
12
13void pumpOn() {
14  digitalWrite(PUMP_PIN, HIGH);
15  digitalWrite(LED_PIN, HIGH);
16}
17
18void pumpOff() {
19  digitalWrite(PUMP_PIN, LOW);
20  digitalWrite(LED_PIN, LOW);
21}
22
23void setup() {
24  pinMode(IR_PIN, INPUT);
25  pinMode(PUMP_PIN, OUTPUT);
26  pinMode(LED_PIN, OUTPUT);
27  Serial.begin(9600);
28}
29
30void loop() {
31  bool handDetected = digitalRead(IR_PIN) == LOW;
32  unsigned long now = millis();
33
34  switch (state) {
35    case IDLE:
36      if (handDetected) {               // Hand under the nozzle
37        state = DISPENSING;
38        stateStart = now;
39        pumpOn();
40        Serial.println("HAND -> PUMP ON");
41      }
42      break;
43
44    case DISPENSING:
45      if (now - stateStart >= PUMP_TIME) {  // Dose complete
46        pumpOff();
47        state = WAIT;
48        stateStart = now;
49        Serial.println("DOSE DONE -> LOCKOUT");
50      }
51      break;
52
53    case WAIT:
54      if (now - stateStart >= LOCKOUT) {
55        state = IDLE;
56      }
57      break;
58  }
59}