Smart Shopping Trolley that Follows Customer

Smart Shopping Trolley that Follows Customer

Image: Mini grocery toy pushcart.jpg by Me (Elsa Versailles) via Wikimedia Commons, Public domain

How It Works

• An IR sensor array on the trolley's underside reads reflective floor guides or an IR beacon carried by the customer, giving the controller a directional reference to steer by.
• Two or more ultrasonic sensors (front-facing) continuously measure the gap between the trolley and the customer; the controller uses this reading to modulate motor speed via the motor driver.
• If the measured distance drops below a safe threshold (customer stopped or turned back), the trolley slows and halts; if the gap widens beyond the tracking range, it speeds up to catch up, within a capped maximum speed for safety.
• DC motors via a motor driver (L298N) provide smooth, low-speed propulsion suited to indoor aisle navigation, with an obstacle-stop override if something unexpected — another cart, a person crossing — enters the path.

Components

Arduino Uno/Mega
IR sensor array (line/lane guidance)
Ultrasonic distance sensors (HC-SR04) x2–3
Motor driver module (L298N)
DC gear motors + wheels
Handheld IR/RF beacon transmitter (carried by the customer)
Rechargeable battery pack
Trolley chassis/basket frame

Applications

• Supermarkets and hypermarkets
• Shopping malls and large-format retail stores
• Warehouse and wholesale club assistance
• Accessibility support for elderly or mobility-limited shoppers

Advantages

• Removes the physical effort of pushing a loaded cart
• Improves accessibility for elderly and mobility-limited customers
• Gives physical retailers a tangible, differentiating in-store experience
• Obstacle-aware stopping keeps the design safe around other shoppers

Sample Code — Distance-Based Follow Logic

// Simplified follow-distance control — Arduino
#define TRIG 9
#define ECHO 10
#define MOTOR_A 5
#define MOTOR_B 6

long readDistanceCM() {
  digitalWrite(TRIG, LOW); delayMicroseconds(2);
  digitalWrite(TRIG, HIGH); delayMicroseconds(10);
  digitalWrite(TRIG, LOW);
  long duration = pulseIn(ECHO, HIGH);
  return duration * 0.034 / 2;
}

void setup() {
  pinMode(TRIG, OUTPUT);
  pinMode(ECHO, INPUT);
  pinMode(MOTOR_A, OUTPUT);
  pinMode(MOTOR_B, OUTPUT);
  Serial.begin(9600);
}

void loop() {
  long dist = readDistanceCM();
  Serial.println(dist);

  if (dist > 80) {
    analogWrite(MOTOR_A, 0); analogWrite(MOTOR_B, 0); // too far / lost - stop
  } else if (dist > 40) {
    analogWrite(MOTOR_A, 150); analogWrite(MOTOR_B, 150); // catch up
  } else if (dist > 20) {
    analogWrite(MOTOR_A, 90); analogWrite(MOTOR_B, 90);   // hold gap
  } else {
    analogWrite(MOTOR_A, 0); analogWrite(MOTOR_B, 0);     // too close - stop
  }
  delay(100);
}

Related Research

• The IoT-Based Smart Shopping Trolley System — IEEE Xplore