How to read and write to an unknown RFID chip

Hello all,
I am new here, I hope I am posting in the correct area. I have a box of what appears to be identical passive RFID chips (round, about 1 inch in diameter, about 2mm thick). I would like to read them and then be able to change the data on them. How do I choose a tool that would allow me to work with them? I do know that they are intended for very short distance reading and writing (less than a few cm). I understand that there are
Thanks for your help!
Doc

First you have to identify the RFID standrad implemented by the chip. ISO/IEC 14443 (13.56 MHz) would be a promising candidate, but is may be also a low frequency (e.g. 125 kHz) standard, or some less common protocol. A 13.56 MHz standard would be most simply identified by trying to read out the chip with a multiprotocol RFID reader.You may want to use a grid dipper or an equivalent measurement circuit to check, if the part shows a RF resonance at a certain frequency.

You're possibly not able to read out all data stored in the chip, because it may implement security features. But it should at least identify with a serial number. The chip may be also read-only, not intended to write any data.

I have the device that comes with the chips that reads and writes to the chips. I do not have any specs, but it is working. Once the chip has been read, the counter advances and the chip can not be read again. Can you suggest some devices for me to try? If you can give me the name and brand of the device, or a link, I can look them up. Apparently there are quite a few models available on eBay. From you answer I assume I could use a "grid dipper" to evaluate either the chip or the device that I have that reads and writes to the chip. I would also need a device that could read the chip in it's before and after state and then another device to write to the chip?

Thanks again for your help.

Doc

I have the device that comes with the chips that reads and writes to the chips.

Click to expand...

In this case, you can wind of few wire turns as a montor coil, connect an oscilloscope and try to detect the carrier frequency as a first step. To identify the protocol, some deeper knowledge of RFID would be needed. You can find introducing literature at the internet.

If the application of the chip is a professional designed payment system, you should expect strong cryptography implemented within. Then simply forget about it.

There is no money involved with these chips, at least not directly. They are actually used to start a timer. When the chip gets read, the timer starts and goes for 4 hours and counter gets increased by 1 unit. After 4 hours, the machine turns off and another chip is needed to start the machine working again. After a chip has been read, it can no longer be used to restart the machine. I assume the chip is somehow modified, or perhaps each chip has a serial number and the machine keeps track of all the serial number it has ever read. I think the chip is probably modified because I don't think it will work on any other similar machine after it has been read once. What should I look for as far a read write device is concerned? Do any of the devices work with multiple protocols?
Doc