next topic »

[on:]

Hello There,

I am working on a Project for wich I need the ability to determine the location of multiple balls in a bowl and controlling 3 different LED colors in the ball.

At first I wanted to use XBee modules and time measureing to do that, but some research showed that, this is not possible because it's just too fast.

So I want to use RFID.
Every ball, wich is about 4cm(1.6in) to 5cm(1.9in) in diameter, has a RFID Tag, and a reader. By knowing wich balls are near a ball, and where the bowls wall is, i can determine the positions of all balls.

The  DIY-Reader (http://arduino.cc/playground/Main/DIYRFIDReader) seems to be great for this job, because I can do the coils myself so they fit to the ball.

Is it possible to use the DIY-Reader to scan multiple tags in range?


I want to use a XBee module to send the neighbours to a computer, wich does the logic stuff, and then sets the balls LEDs.

Will this be possible with the Arduino Pro Mini?
I am worried about the amount off connectors, because I need to connect the RFID-Reader, the XBee module, and 3 LEDs (actually more, because I need to illuminate the ball, but I need 3 colors).

[Reply #1 on:]

By knowing wich balls are near a ball, and where the bowls wall is, i can determine the positions of all balls.

That sounds like a leap of faith to me. I don't think you have very much control over the range of the RFID, so it may not be easy to reliably sense all the touching balls without also sensing some that are further away. Assuming you can manage that, then calculating the physical geometry of a set of balls based on which ones are touching is probably not feasible unless you constrain the balls to a known layout (in a line, for example) - if they're just tumbling around in a bucket I don't think you have enough information to calculate their positions.

[Reply #2 on:]

My experience is that the simple rfid readers are not able to discriminate amongst multiple tags read at once.  If you bring 3 tags in range at once, you may be able to read one tag, but more likely will not read any tags at all.  The tags are really dumb, and will all talk at once when they are placed in the reader's field and the reader is not super-great at discriminating the garbled tag info.  Maybe addressable programmable tags could do it, I'm not sure.

I wonder if you could do what you want with those cheap SAW based radios.  Have each ball peep out its identity at intervals and have a receiver near the bowl able to receive the signals of balls within -- say -- a metre.

[Reply #3 on:]

So it could be a solution to build my own Tags, wich I can read then.

I've found these articles. As I understand the word "spoofing" it actually means they are selfmade Tags.
http://www.instructables.com/id/Stupid-Simple-Arduino-LF-RFID-Tag-Spoofer/
http://wiki.smallroom.net/doku.php?id=terd:projects:rfidspoofer

With these it should be possible to implement an algorithm wich makes sure only one tag is readable at the time.
Do I get it right?