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Topic: Single RFID-reader multiple antenna (Read 2778 times) previous topic - next topic

Jabrwock

Looking to have an interactive skeleton, where kids can place bones in spots to try to correctly assemble the animal.

RFID buttons on the bottom "plug" of each part, location lights up LED if part is in correct hole on the board (10 to chose from).

To cut down on cost I'd like to only have one RFID reader, with the Arduino cycling through a mux to read a single antenna at a time to see if the correct RFID tag is at that location.

I'm looking at the ID-3LA RFID reader (uses external antenna 125Khz) and using 4 ADG904 antenna switches as the mux (3 to cover the 10 spots, one to mux between those 3).

Does this sound feasible? I'm not well versed in RF sensitivities.

rogerClark

I don't think using MUX will work, as the signals need to go both ways

You could try using audio relays, but I suspect it would be cheaper just to buy a batch of readers from one of the Chinese companies

But I guess using multiple rs232 based readers would be an equal problem as you'd need to MUX the rs232 to the readers.
I suspect you'd end up needing a mini arduino per reader and then communicate to a master ardunio on i2c
Freelance developer and IT consultant
www.rogerclark.net

Grumpy_Mike


Does this sound feasible?

No, while a multiplexer would transfer the signal both ways you will find that the voltage on an RFID coil is in the order of 100V or so and this exceeds the voltage capacity of a multiplexer. The signals have to be within it's power supply.

Theoretically you could make your own two coil RFID reader and have a separate receive coil multiplexed, but this takes some skill and test equipment to achieve. Still if you want to see what is involved have a look at this project of mine.
http://www.thebox.myzen.co.uk/Hardware/RFID_Sequencer.html

Jabrwock

Theoretically you could make your own two coil RFID reader and have a separate receive coil multiplexed, but this takes some skill and test equipment to achieve. Still if you want to see what is involved have a look at this project of mine.
Texas Instruments's 16 antenna design using RF switches doesn't go the two coil route, with only 4 inches between antenna coils. I'm curious why you went with the two coil design?

http://www.ti.com/lit/an/sloa167/sloa167.pdf

Grumpy_Mike

That chip is for 13.56MHz and you can't get tokens of the sort I wanted to use at those frequencies, and even if you could I already had a bag of the tokens I used so I wanted to go with that.
I used a two coil design so I could multiplex the lower level received signal and have the power driver to the common coil.

However I hadn't see that chip so thanks for sharing, I might use it one day.

johnfoneill

I'm interested if you've found a suitable solution for multiple antennas using a single Reader?

Thanks,
john

Jabrwock


I'm interested if you've found a suitable solution for multiple antennas using a single Reader?
I haven't finalized the design yet but I settled on a Texas Instruments TRF7960 13.56Mhz RFID reader, coupled with the Analog Devices ADG904-BRUZ 4-input RF antenna switch. The ADG904 can be daisy chained so the 4th input is the output of the next 904.

The design is based off TI's design document I posted earlier in the thread.

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