Overview

This site is about building an RFID reader...

I suspect I'm going to need to start with a chip like the ID-12, a bread-board and some specs for attaching the chip to the serial port of a PC. The ID-12 chip should be able to dump read RFID tag ids down onto the serial port - hopefully this can be read straight off a device.

Innovation ID-12

The innovation ID-12 chip: 

The ID-12, as it’s named, even includes the field coil, making this an extremely compact and easy-to-assemble project.

A continuous 125kHz carrier signal is radiated from the ID-12’s coil while ever power is applied. When a tag is brought within range, its field coil is magnetically coupled to the reader’s coil, inducing an AC voltage across it.

Most 125kHz read-only tags contain just a single IC along with the coil itself, which consists of many turns of super-fine copper wire. To reduce overall size, the coils used in miniature glass and epoxy-encapsulated tags are wound on tiny ferrite cores.

Included in the IC in the tag are circuits to rectify and filter the voltage from the coil, to provide operating power. Once sufficient power has been stored, the tag transmits its 40-bit ID code by low-frequency modulation of the reader’s carrier signal.

For those interested, the data stream is Manchester encoded and transmitted using an ASK (amplitude shift keying) modulation method. To learn more about how this works, refer to the RFID feature in the July 2003 issue of SILICON CHIP.

As shown on the circuit diagram (Fig.1), the interface between the ID-12 reader (IC2) and the rest of the circuit is very simple indeed.

Whenever the reader receives a tag transmission, it formats the 40-bit code into five 8-bit bytes and adds a few bytes for synchronisation and integrity checking. The entire "frame" is then transmitted in serial format from pin 9.

Three different industry-standard transmission formats are supported, selectable by connecting pin 7 to various points. By grounding this pin, our design uses a 9600 bps (bits per second) ASCII format.

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Figure 1 - the ID-12 Security Module kit

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Figure 2 - the ID-12 chips

Here is the ID Innovations data sheet for the ID-12 chip: ID_SERIES_DATASHEET_2004-2-10_rev13.pdf

External Reference Sites

Reference sites:

Maker of the ID-12 chip:

Vendors of ID-12 chips:

RFID Vendors:

BradsWiki: RfidWip (last edited 2005-10-25 14:03:53 by BradleyDean)