security lock using rfid

sir/madam,
i know the basic working of passive rfid tag n reader...
i want to design a system to protect milk frm getting adulterated and thus providing rf tag-lock system to MILKVAN. can u please help me how i can do this using AT89V51RD2....

I had an idea in mind wherein there will b an antenna at remote location that emits RF frequency and i will have a circuit in my van where RF freq. will be detected and will b matched with the pre-stored code unique for a freq. and then further when the code matches the lock on the van should b opened.

is this idea practically implenmentable??

If not please suggest me a suitable solution for the same usin rfid.

I dont know at what distance you want to operate.
A standard rfid reader for passive tags works at short distance. About 6 inches at maximum. There are long range readers but the cost rises.
Door locks based on rfid are available, ready made. If you want your own application with the AT89 you can get a rfid reader and interface it. Common interfaces are RS485 and wiegand but RS232 or TTL serial may be available.
Passive rfid tags emits the code when the field of the reader is high enough to generate the voltage necessary for the internal chip to operate. Only the reader generates RF, the tag modulates the readers signal with the code.
As I said before the idea is already implemented in door locks and other access systems. At short range is very easy.
Long range is way more difficult but doable like the automatic toll in highways. That used active rfid tags but now were replaced by passive tags stick to the windshield.

plzz help.........

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plzz help.........

vishal2610 said:

plzz help.........

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plzz help.........

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What help you need is still unclear for Albert here has clearly pointed out all that you need

If you need more info then you need to tell where you are stuck and what exactly you need to get any further help