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Congratulations on the design of such an elegant RFID reader. I have built one based on your design and it works beautifully with standard cards. I have also seen your posts on building RFID tags using only an AVR ATtiny85 controller (or a controller with an antenna and caps) and am in the process of trying to build some of these as well. My question is whether you think that the ATtiny85 could be modified to act as a sensor rather than just sending back a number, such that the number sent back could be modified by a detected voltage. I am hoping that with relatively simple modifications to your tag as designed, one could make remote sensing devices, still operating in the passive mode without the necessity for battery power. Thanks again for sharing your designs.