IoT Smart Shopping Trolley with Smart Lid and Direct Billing

Billing queues and repeated manual scanning of every item remain a persistent bottleneck in small and mid-sized Indian retail stores. This paper presents the design, fabrication and testing of a low-cost IoT shopping trolley that identifies products as they are placed in the cart, verifies each addition by weight, displays a live running bill on an acrylic smart lid, and sends the finished bill directly to the billing counter over Wi-Fi. The system combines an ESP32 microcontroller, an MFRC522 13.56 MHz RFID reader, a 40 kg load cell with an HX711 24-bit ADC, a 16x2 I2C LCD and SG90 servo latches, mounted on a mild steel chassis built for a 25 kg payload. A dual-parameter rule accepts an item only when its tag identity and its measured weight change agree within a tolerance of max(5% of reference mass, 10 g). A bending analysis of the chassis gives a factor of safety of 14.6, and a queueing model predicts a large drop in counter waiting time. In bench and field trials, 184 of 185 verification trials were handled correctly (99.46%), and checkout time stayed between 22 and 25 s for baskets of 5 to 25 items, against 135 to 515 s at a conventional counter. A usability demonstration with 120 participants in a Kopargaon supermarket was received positively, particularly by senior citizens