Multiple NCF Readers

Download the code or see the schematic

For a recent lab project, we needed to be able to read NFC tags from 12 readers at once. Strong Link makes affordable NFC readers that use I2C communication. The model we use is the SL018 which Marc Boon has conveniently created an Arduino library for!

It’s pretty straight forward running the Arduino sample code for a single reader using the example code in the library. Two readers worked fine with the multireader example, but more than that, the system would become increasingly unreliable. The solution was to continuously poll each reader using a HCF4156BC multiplexer. Since these NFC readers used I2C communication to transmit data it was necessary to have a separate multiplexers for SCL, SDA, and active line. Each multiplexer has 8 inputs so it required 6 multiplexers total. The binary control inputs and common output pin could all be chained by using the inhibit pin to select which set of multiplexers were being read from.

The code provided reads the ID of the tag as well as indicates when the tag has left the reader. The example schematic only shows one reader, but you would hook up all the readers in the same way. The 2.2k resistors is the resistance value that allowed a clean read from the Arduino. You can read this if you’d like to understand more about the science behind the resistor values. Changing the number of readers may require a different resistor value. RJ45 connectors reduce the number of wires and make the system a bit more modular.

Parts list:

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