DIY FSK RFID Reader using Arduino

This page is describes the construction of an RFID reader using only an Arduino (Nano 3. 0 was tested, but others may work), a hand-wound wire coil, and some assorted low cost common components. RFID readers are devices sold by companies such as Parallax to read RFID tags with embedded identification circuits (we focus here on passive tags, activat
DIY FSK RFID Reader using Arduino - schematic

ed by the reader`s transmitted RF energy). The design presented here shows how to wind a simple wire loop by hand (or create an equivalent printed circuit spiral version), connect it to an Arduino (or its chip), add a few low cost common components and create your own RFID reader. To make it more interesting (i. e. challenging), we will focus on the FSK class of RFID tags, which are fairly common among the 125kHz devices, but for some reason are not supported by the Parallax kits. Micah Dowty has shown a design for an FSK/ASK RFID reader built around a Parallax Propeller device. His code, which is in assembly language, implements an ingenious (but complex) algorithm to create a dynamically variable analog bias voltage, which is used to pull the weak RFID signal into range, so it can be discriminated into binary signals by the Propeller`s digital input circuitry. He also dynamically tweaks the transmit/receive RF frequency to keep the antenna`s tank circuit in peak resonance for optimal signal to noise. There are three problems with his approach: first, the passive detection circuit lacks amplification, which makes it very sensitive to noise and therefore raises reliability issues. Second, the design is based on the Propeller chip, and if you are a fan of the Arduino and/or associated Atmel AVR chips, it leaves you out. And third, the dynamic slewing of frequencies and bias voltage is overly complicated, making it hard to...

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