I'm looking to build a timing system base on passive RFID transponder. This is how I see it :

  • An antenna to "question" the tag
  • An antenna to receive tag unique ID
  • A tag with unique ID

I would like to buy a lot of transponders on internet (like this one). My question is :

If I want to build my own antenna, is this reasonable possible to do? From there, where should I start looking for technical information about those system?

What about the "questioning" antenna? It doesn't seem to be really complicated. How is it working?

My question may be too evasive for some of you, but is still relate to circuit designing. Any answer will help me to identify more precise questions.


The timing system would be for running event. So, I won't need a system really fast for this

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    \$\begingroup\$ What is the timing system for? What speeds are you expecting for the moving object? As somebody who spent a long time looking at this I can advise it might not be the best idea! \$\endgroup\$ – David Aug 22 '14 at 9:59
  • \$\begingroup\$ I would really like to heard your experiment into this? What difficulties did you have? \$\endgroup\$ – Boris88 Aug 22 '14 at 12:08
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    \$\begingroup\$ In response to your update you will want to very carefully test that the activated receiver coil is large enough that all runners will be over it for long enough to register. You will also need a collision avoidance strategy (as you can't read multiple tags at once), or funnel runners through single file. \$\endgroup\$ – David Aug 22 '14 at 12:09
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    \$\begingroup\$ I was doing this for timing go karts, which required active transponders (the term isn't normally used like this, but it's common in timing to call it such). \$\endgroup\$ – David Aug 22 '14 at 12:24

The "questioning" antenna provides the power to the RFID tag that contains a circuit to provide the tag ID back. The whole system can be thought of like a transformer. The number of wire turns in the "questioning" antenna and the number of wire turns in the tag have to be at a particular ratio so the tag gets the proper voltage. It is going to be a rather involved undertaking. You also have to take frequency and power into consideration. The little devices used to open doors with these tags require less power than something that requires reading at a distance because you usually have to "touch" these cards to the readers.

Here is some reading to get you started: http://edn.com/design/wireless-networking/4341980/Optimizing-read-range-in-RFID-systems

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