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I had to put together one of these recently for a building and thought it would be interesting to see what I could come up with.
I'd bought a cheap RFID reader some time ago from Ebay or Amazon just to play around with and my first inclination for this project was to just use one of those things and somehow embed it in some sort of box and mount it on the wall outside and then somehow interface that back to a central location over 50 feet or so of wire. The following image is pretty much what I had experimented with in the past.
These things have an SPI interface which means sending data over a long wire is not really an option so that means slapping some microcontroller nearby in the wall and then having that talk to the central location. This was starting to get ridiculous!
After some more reading it became clear that what was needed was a Wiegand interface card reader. There's plenty of information out there about Wiegand. It's pretty much an industry standard which is good and means lots of card readers available for cheap. What also appealed to me was it was good for longer distances. I grabbed a 13.56Mhz (I had a few 13.56Mhz cards and key fobs already) version off Ebay for about $14.
A card reader like this is an obvious choice as it's self contained and waterproof so no messing around as I mentioned earlier with that cheap SPI thing and mounting issues etc! (what was I thinking???)
Front of card reader:
Back of card reader. Nice and easy to deploy!
RED VCC BLACK GND GREEN D0 WHITE D1 YELLOW BUZZER BLUE LED BROWN FORMAT
There was already some 8 or 10 core cable (can't remember offhand which) pulled to the location where the card reader was to be deployed so it was just a matter of joining those wires and attaching it to the wall.
That's about it for the "Reader" side of things. On the next page I get into the "brains" of the system.
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