Travels with RFID pt 1

Basically I have been fascinated by RFID for ages, but as per normal done nothing about it

This project (thinly guised as for my employer) but essentially a good exercise in RFID, Linux, PHP , SQL etc, is basically a ground up build of an RFID circuit, that reports back to a server and logs peoples times in and out of the workplace for checking hours worked and to pay them the right amounts.

Pt one was to find an RFID solution that i could fairly easily connect to a PC

my requirements here are :
1. its cheap enough that if it all goes pearshaped i dont feel i've wasted toooo much money.

2. its as basic as it can be for learning purposes (ie its not pre-built with proprietry software) . This is to allow me to put it into windows or linux machines (much chinese stuff comes with windows only software etc)

3. it works

I looked at several options. Most of which involved either basic stamp electronic building blocks or parallax or arduino. The other problem is that most systems need to be bought from either Europe or USA neither of which satisfies my need for things NOW - god i can be impatient.

I worked out that i basically could use the www.id-innovations.com ID-12 RFID reader and for the life of me could only find it locally in an electronics kit at www.jaycar.co.nz KC5393

So not so much reverse engineering but re-engineering was required.

What most of these units for sale do is store the RFID card data on an eeprom and then when the correct card is shown - engerise a relay to open a door. So i realised that most of the circuitry on this kit, including the microprocessor and peripheral circuitry for the microprocessor was useless for what i wanted.