There are many uses for RFID such as supply chain management, but access control is one of the most relevant applications for personal use. Many people use RFID access cards to get into buildings, use elevators, or even open the doors to those special penthouse type hotel suites. Setting up your own front door (or any door for that matter) with an RFID enabled access mechanism is pretty easy.
Electronic Strike
Most access control solutions use an electronic door strike, which gives way
when activated so you don't have to unlock or turn the doorknob; you just push
(or pull) the door open. This is exactly what's used to "buzz" someone
in a door. That buzzing sound is AC power rushing through the magnetic coil
windings in the door strike, pulling up and vibrating the pin that normally
keeps the strike in the closed and locked position. You're going to use DC power
to operate your electronic strike, so all you should hear is a slight click.
There are many different kinds of strikes out there. Figure 1 shows a couple
of different products from two different manufacturers. Some are small and
expensive, and some are larger and fairly cheap. The important thing is that it
fits your doorframe, and uses DC power between 5 and 12 volts to activate.
Electronic Deadbolt
If you use a deadbolt to secure your front door, the electronic strike isn't the
best solution. The strike is designed so that you can push the door open without
needing to retract the door latch. But when the door closes, the latch in the
door is designed to push inward and snap back into place behind the strike. A
deadbolt won't retract when the door closes, it will smash loudly against the
strike and possibly damage the door, the strike, the doorframe, or any
combination of the three. It would be the same result as if you opened your
door, locked the deadbolt with the door open, and then tried to slam the door
closed.
One solution to the deadbolt problem involves getting one of those keypad
deadbolts like the one shown in Figure 2. It's a deadbolt that lets you use a
standard door key or a number combination entered on a front keypad to retract
the deadbolt and unlock the door. If you have a deadbolt in your front door and
want to use RFID to get inside, you're going to need to get an electronic strike
and hack up one of these keypad deadbolts as well.
Caution
There are actual electronic deadbolts available that function like the
electronic strike. They retract when power is applied, but they don't have the
option of unlocking with a standard key. You don't want to be stuck outside
because of a power outage or some other kind of Murphy's Law type problem, so
that kind of electronic deadbolt is out.
Authored by
Amal Graafstra at
ExtremeTech, Added: 2 Apr 2006
http://www.extremetech.com/article2/0,1697,1938953,00.asp
