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RFID Checkout System Design using ATmega644 microcontroller

The Elevator Pitch

We successfully implemented a prototype RFID checkout system that will enable consumers to instantly pay for their entire purchase upon arrival at the register, increasing customer satisfaction, reducing retailer costs, and ultimately lowering consumer prices.

rfid system


Shopping in the present day usually involves waiting in line to get your items scanned for checkout. This can result in a great deal of wasted time for customers. Furthermore, the technology currently used in checkouts � barcodes – is from another era, developed in the 1970s, before the age of the affordable computing power. In the present world, with computers powering everyday items from children�s toys to wristwatches, we felt like we can improve on the humble shopping experience.

With the increasing prevalence and affordability of radio frequency identification (RFID) tags in everyday authentication systems, RFID holds great promise in the retail world for both customers and stores in inventory control, convenience, and cost savings. Our project utilized these RFID tags to automate the checkout process by building a system that could read the RFID signals of all the objects that were placed in proximity to an antenna platform. This eliminated the need for barcode scanning of each individual item, making checkout a significantly faster experience. Furthermore, as each item has a unique tag, even copies of the same product contrasted to the current UPC model, much better inventory control, recall ability, and monitoring of consumer behavior trends are possible, with privacy concerns considered of course.

High Level Design

Rationale and Motivation for Project

Jigar’s mother has been a cashier at their local Walmart for over 15 years. One day, she was so tired from work and discussed with Jigar the possibility of technology completely taking over the job of a cashier. As we had been exploring project ideas for this course at the time, we immediately began to consider the practicality of such a proposition, and whether we could indeed implement a prototype of such a system for our final project.

We immediately considered RFID tags, already used heavily at Cornell for dorm access, not to mention in industry for employee authentication and credit card systems for wireless payment. For those applications, however, only one tag at a time was read, and multiple tags within the sensor read area would render the system useless, a key requirement of our checkout system. We discovered that a mainstream tag protocol had been developed at 13.56 MHz with anti-collision support, enabling simultaneous, error-free reading of all tags within the read field.

Last but not least, we had to consider whether such a system would be cost-prohibitive. When doing parts research, we discovered comprehensive reader chips available at less than $100 each that could be integrated into existing self-checkout systems. We came across news articles that showed research leading to tags that could cost less than 5 cents each, with cost decreasing over time.

Background Math

The particular RFID tags we will use in our project are passive RFID tags. This means that it relies on power transmitted by the reader in order to operate. In operation, passive RFID tags use the reflected carrier frequency (cos(wt)) which is modulated with a function (m(t)) in order to transmit information.

Image 1

In this modulation function, the data has been hardcoded in the tag and can be transmitted to the RFID reader in a binary fashion.

Two major methodologies of modulation in our RFID tags include Amplitude-Shift Keying and Frequency-Shift Keying. In Amplitude-Shift Keying, two discrete amplitude levels are applied to the sinusoidal carrier frequency to represent 1’s and 0’s. This is illustrated below:

In Frequency-Shift Keying, two different frequencies are used to indicate binary values. This is done by switching between two different oscillators that are connected to the output. This is illustrated below.

In order to allow reads in electromagnetically noisy environments, readers are tuned to only read one particular frequency – in our case, the SkyeModule M1 reader we are using only reads radio frequencies of 13.56 MHz.

In cases where there is more than one tag in the vicinity of the reader, tag collision may occur when both tags reflect their signals back to the reader at the same time. This can confuse the reader. Thus, various methodologies for anti-collision can be used. These methodologies vary by tag type.


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