RFID help needed for Cornhole scoring

[STMartin]

For Christmas, my siblings and I have decided to build my father a bag toss (cornhole) set. (I'm not sure how prevalent the game is outside the US, so here's a Wikipedia link if you're unfamiliar with it: https://en.wikipedia.org/wiki/Cornhole).

Anyway, I figured my contribution would be to develop an automated scoring system. The plan at the moment is to incorporate a passive RFID tag inside each bag before they are sewn up. On the boards themselves will be two RFID readers, one long range (about 15 feet/4.5 meters) and one short range (about 6 inches/15 cm). The short range reader will be near the hole. Also on each board will be two (possibly four) weight sensors; placed under the back legs, or at all four corners if needed. The premise for detecting a toss/point is this:

Bag Action	Long range RFID detected?	Short range RFID detected?	Weight change detected?
Complete miss	Yes	No	No
Landed on board	Yes	No	Yes
Landed in hole	Yes	Yes	No

I've never worked with RFID before, so to those more knowledgeable, I have a few questions.

1)Can I use any tag with any reader, as long as they both operate on the same frequency?
I am aware of tag collision, and I know I need a reader that can handle reading multiple tags simultaneously. Do I need special tags too?

2)How do I determine the reader range?
It seems to be dependent on the antenna. However, even the antenna datasheets don't say anything specific. Is there a calculation I could use? Or do I need to determine it experimentally?

3)Can I programmatically change the reader's transmit power?
If so, I'd only need one reader per board, and could dial in the power to get the range I want.

4)Are passive tags even capable of a ~15 foot/ 4.5 meter range?
Batteries inside the bags are simply out of the question.

5)How much does the tag's orientation matter?
The tag will be floating around inside the bag, so there's no telling what side will be facing the reader.

6)Will a reader be able to detect a bag in the air, or one on the ground?

7)Any other things I should consider?

I am also aware of reader collision. If I need to use two readers, they'll be time-division multiplexed.

[helius]

1. Can I use any tag with any reader, as long as they both operate on the same frequency?
No, because there are different modulations supported by different tags, and different command/data formats. There are standards involved (EPCglobal Gen2, ISO 18000) and careful reading of spec sheets will list standards compliance.

4. Are passive tags even capable of a ~15 foot/ 4.5 meter range?
Yes, UHF tags are capable of 20 foot range. There are really two totally different passive principles: near-field coupling, where the reader and the tag both have a coil and they couple magnetic flux to communicate; and far-field transmission, where the reader and the tag have tuned antennas that transmit and receive EM waves. The field attenuation with distance is \$ {1\over r^6} \$ for the near-field, but just \$ {1\over r^2} \$ for the far-field, which makes communication possible at much longer distances.

Specialized passive tags and readers are capable of 80 foot or even 300 foot read ranges.

5. How much does the tag's orientation matter?
It depends on the frequency and type of the tag. UHF and microwave tags are suited for any-orientation operation, while other tags depend on orientation to inductively couple with the reader.