Practical 8

Visitor / Object Counter System

Bidirectional counting with live display

Aim

To count people or objects entering and leaving a room using two detection points, and to display the live occupancy count on a display module.

Overview

Two PIR motion sensors (or IR beams) are placed in a line at the doorway. The order in which they trigger determines the direction: sensor A then B means someone entered, sensor B then A means someone left. The Arduino keeps the count between 0 and the room capacity and shows it on a 2-digit 7-segment display. A buzzer and a red LED warn when the room is full.

Components Required

Arduino Uno
2 x PIR motion sensor (HC-SR501) or IR beam pairs
2-digit 7-segment display (common cathode) or SevSeg compatible display
Buzzer
Red LED (room full indicator)
Breadboard and jumper wires

Circuit Connections

From	To	Note
PIR A OUT	Arduino D2	Entrance direction reference
PIR B OUT	Arduino D3	-
PIR VCC / GND	Arduino 5V / GND	-
7-seg segment a-g, dp	Arduino D4-D11	Each via 220R resistor
Digit 1 / Digit 2 common	Arduino D12 / D13	Multiplexed digits
Buzzer +	External pin or transistor on A0	-
Red LED (via 220R)	Arduino A1	-

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 watches both PIR outputs for rising edges (motion detected).
A small state machine records the trigger order: A,B = ENTRY (+1); B,A = EXIT (-1).
The count is clamped to 0..MAX_CAPACITY and pushed to the 7-segment display.
When count == MAX_CAPACITY, the buzzer sounds and the red LED stays ON.
A timeout resets a half-completed sequence so a single stray trigger cannot corrupt the count.

Control Logic

Direction is derived from trigger sequence, not from a single sensor, which is what makes the counter bidirectional. count = clamp(count + delta, 0, MAX). FULL alert whenever count == MAX.

Arduino Code

1// Practical 8: Visitor / Object Counter System
2#include <SevSeg.h>
3
4const int PIR_A = 2;          // First sensor on the entry path
5const int PIR_B = 3;          // Second sensor on the entry path
6const int FULL_LED = A1;
7const int MAX_CAPACITY = 20;
8
9SevSeg sevseg;
10int count = 0;
11
12// Simple sequence tracker: which sensor fired first
13bool aFirst = false, bFirst = false;
14unsigned long lastTrigger = 0;
15const unsigned long SEQ_TIMEOUT = 1500; // ms
16
17bool wasA = false, wasB = false;
18
19void setup() {
20  pinMode(PIR_A, INPUT);
21  pinMode(PIR_B, INPUT);
22  pinMode(FULL_LED, OUTPUT);
23
24  byte numDigits = 2;
25  byte digitPins[] = { 12, 13 };                  // Digit commons
26  byte segmentPins[] = { 4, 5, 6, 7, 8, 9, 10, 11 }; // a,b,c,d,e,f,g,dp
27  bool resistorsOnSegments = true;
28  sevseg.begin(COMMON_CATHODE, numDigits, digitPins, segmentPins,
29               resistorsOnSegments);
30  Serial.begin(9600);
31}
32
33void loop() {
34  bool a = digitalRead(PIR_A);
35  bool b = digitalRead(PIR_B);
36  unsigned long now = millis();
37
38  if (now - lastTrigger > SEQ_TIMEOUT) {    // Reset stale sequence
39    aFirst = false; bFirst = false;
40  }
41
42  if (a && !wasA) {                         // Rising edge on PIR A
43    aFirst = true; lastTrigger = now;
44    if (bFirst) {                           // B then A = leaving
45      count = max(count - 1, 0);
46      Serial.println("EXIT");
47      aFirst = bFirst = false;
48    }
49  }
50  if (b && !wasB) {                         // Rising edge on PIR B
51    bFirst = true; lastTrigger = now;
52    if (aFirst) {                           // A then B = entering
53      count = min(count + 1, MAX_CAPACITY);
54      Serial.println("ENTRY");
55      aFirst = bFirst = false;
56    }
57  }
58  wasA = a; wasB = b;
59
60  bool full = (count >= MAX_CAPACITY);
61  digitalWrite(FULL_LED, full ? HIGH : LOW);
62
63  sevseg.setNumber(count, 0);
64  sevseg.refreshDisplay();
65}