I am currently working on a project where I would
like to detect if a player is holding a ball or not. I want to use
a basketball so placing things on the ball is possible, but inside the ball
gets harder. RFID stickers seem to be the best solution but I can
not find readers that have enough range (10 - 15 cm). The readers
can not be big because they have to be mounted in the bracelets of the players.
Can somebody give me any advice?
Thanks.
Hmmm, tricky.
If the ball was covered in a conductive mesh or paint and the players had gloves, perhaps capacitive or direct electrical sensing in the gloves would work?
Also thought about that, the best part is that they do not even need gloves in that
case. The problem is the ball for me. At least I do not know about any time of conductive
spray/ink/paint that does not crack after 15 bounces. Do you? Thanks
You would be able to get a glass 'pet chipping' RFID bead inside the basket ball through the air valve. Although it would rattle around. But yes, sensing from any kind of range is going to be difficult without big high powered RFID reader technology.
Tricky!
I would test capacitance sensors first...
Here is a fancy industrial sensor
http://www.omron-ap.com/product_info/E2J/index.asp
A capacitive effect could change an oscillator frequency...
http://www.cs.cmu.edu/afs/cs.cmu.edu/Web/People/ram/capsense/intro.html
It might have to be tuned to the person.
Since you have to exert pressure to hold the ball you could do the bio-med stuff and check muscle signals -- but that is too tough for most people.
More thoughts
There is nothing wrong with doing a google search for a proximity sensor -- something you should have already done...
Use your imagination... Design your own capacitance sensor -- it should not be difficult.
This does not look like a difficult project unless you want it to be...
Can we assume the ball will be held within two hands?
If so, then if the ball had a conductive coating, then you could do something with the change in resistance across the player's arms.
Or put 220V on opposite sides of the ball and have a microphone for each player's screams 
MarkT:
Or put 220V on opposite sides of the ball and have a microphone for each player's screams
I'm voting for this solution as the "cleanest". ]