Engineering an RFID reader

The development of an RFID system for use with 8th period attendance at TJHSST.

This project is a self-made RFID reader. Using mutual inductor coupling and amplitude shift keying, I turn the interaction between the reader and tag into binary data which can be used by a software program and connected to Ion, TJHSST's student and teacher intranet.

Inductor Coupling

RFID readers rely on the fact that both the reader and tag have inductors, components which store current in a magnetic field when it passes through. When the tag is in the presence of the reader's magnetic field, it activates and intermittently puts a load on the reader's inductor. When the load is present, the voltage will decrease, meaning there are periods of lower voltage caused by the tag.

1 0 1 0 1 0 1 0 0

Here, you can see coupling in action. The low points of the blue signal represent when the tag is putting a load on the reader's coil. The highs are when the coil is unimpeded.

This sequence in particular would be: 101010100

This circuit resonates at 125Khz, which is the standard resonant frequency of the tags I am using.

Full Theory

Schematic

My current full schematic.

Individual parts

An individual look at each segment that makes this project work

Applications:

At TJHSST and other schools, students often spend much of their time every day sitting while a teacher takes attendance. This project hopes to speed up the process using the RFID reader to quickly identify by his or her ID card. The initial idea was for 8th period club attendance, but a broader application is for general classroom attendance.

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