I am very curious as to how these things work. All I know at the moment is that they use RF and are programable. Any more in depth info. would be great.
Well lets see. If you cut open the card you will find two things. Fisrt is a large loop of copper wire that runs about a (1/4) inch inside the edge of the card (except at the top which has more room so that a hole can be punched through it). The second thing you will notice is a tiny little microchip that has both ends of the copper wire soldered onto it. This little chip, in general, has two things programmed into it. The first thing that is programmed is the card’s serial number. Some cards have 3 or 4 digit serial numbers, other have more. It all depends on the manufacturor.
The second thing that is programmed into the chip is the “site code.” Basically this is a group code for the cards.
Example.
Company A and B both use the exact same badging system from the same manufactror. Company A and B both have issued 200 cards to their employees. So both companies have an employee that has card number, lets say, 150. What the site code does is prevent card number 150 from being used at both buildings (this assumes that the company who installed and designed the badging system insured that the site code he ordered is not in use in the area).
Now the second half of this equation is the prox reader itself. As you said in the OP, these readers have a RF field around them so that when a card comes within, in general, 1-2 inches of the reader, the RF field will detect the chip, read the serial number, and then it lets you in. (A lot more happens after you scan the badge, but you didn’t request that info in the OP. If you would like to know simply post that and I will fill in the rest).
Off Topic kind of- Since I am the kind of guy who loves to take things apart I cut open one of these badges at my work. I then CAREFULLY removed the copper wire and chip inside, rolled it all into a little ball, covered it with one layer of tape for protection, and I used this as my badge for about a week. After a week it stopped working, the reason I assume to be because part of the copper wire got cut. It was kind of cool though to be able to scan anything I could fit the little ball into. A lot of employees gave me weird looks when I scanned my coffee mug.
-N
I kind of figured that it would work like that. I am assuming that when they program it that would be where the site code comes into play. The one thing that was bothering me was where it would get power from? I understand that the chip can hold information without power but I also figured it would need some power to transfer that data to the reader. I know that a coil that is passed through an RF feild will generate electricity. Is that how it works or am I off base here. I really appreciate you answering me. I also got a kick out of the coffe mug. How did you learn all the extra stuff? I know you took them apart but that is alot of info for just fiddling with the guts. I would be interested in any info you have on the reader too. If you feel like sharing I will definately want to read it.
Well, I learned all this stuff because I am currently a full time security guard as well as a full time college student, so the two put together breed a certain inquisitiveness. My company also recently bought out another company and I am in charge of integrating the two different security systems. After a while you start to get a really good idea of what the limitations of the system are and what it’s capabilities are. Anyway…
Lets start with the first question about where the card gets it’s power from. First let me say that unfortunetly I have not been able to find the answer to this question. I poked around in our manuals and I asked our installation contractor and neither could give me a good answer. So let me re-enforce that anything I say on this topic is at most an educated guess. With that said lets start at the beginning. Have you ever seen one of thos cordless “sonic” toothbrushes? Robert Eurich (lead role in “Spencer”) does an info-mercial for them and they are sold just about everywhere. Well if you take a look at them you’ll notice that they have no holes in them for you to plug them in to charge. The way they charge is pretty weird and I don’t quite understand how it works. To charge the toothbrush what you do is set it on it’s stand. The toothbrush has a small cone shaped hole in the bottom of it and there is a small cone on the toothbrush stand. You put the two together and the little green light comes on on the toothbrush and it is being chraged. Well I think this is how these badges get their power. When the card comes into the range of the RF field, the RF field generates enough juice for it to signal what it’s serial number and site code is. So we both are thinking the same thing and I think we are on track. Hopefully I will find a definite answer one of these days.
Now, as far as how the rearders work, well you got me. I suppose anyone here who knows how a machine can create an RF field would be able to decribe how that works, personally that is not my field. But what I can and will tell you is what happens after the reader gets it’s signal. When you scan your badge on the reader the info on the card is passed onto the reader. So now the reader knows what the badge number is and what the site code is (to make things simpler we will ignore site code stuff). The reader then sends that info back to the panel. The panel is the intermediary between the reader and the main computer. The way a panel works is that it has a list of all the badges that are programmed into the whole security system. The panel also has a list of exactly which readers each card is allowed to use. So card 100 may be able to be used on say a lobby door but it wont work on the, lets say, radioactive mutant animal lab. So when you scan your badge on the radioactive mutant animal lab door the panel compares your badge number to the list it has of badge numbers that are allowed in that lab. If your on the list your in, if you aren’t then the panel sends a signal to the computer informing the operator of an attempted un-authorized entry. Then, depending on the security dept, you may get a Security Officer beating you up with a flaslight. All badge reads are kept on file in a log and traditionally these logs are kept for 6 months.
If ya have any more question just ask.
-N
I have all the info I need. Thanks a lot. I just get curious about these things. The place where my wife works just got these cards and that is how I got it in my head to find out how they work. Sometimes I wonder if I have too much of this stuff in my head already… 