Need some RF circuit suggestions

[dxpwny]

I would like to build a hopefully simple rf project. I want to have something like this ... but not as complex: RFID tags attached to objects that vary in size and shape. When the objects are placed on a counter top, a light flashes.

All of the RFIDs would be the same - I would never care to tell the objects apart - only their presence on the counter top. Things like weight sensing, light beam blocking detect, etc etc etc are not an option.

I think that is a bit complex in that the RFIDs would require programming (?) and a rfid sensor.

I'm ok with designing everythign except the rf aspect. I have looked at various RF modules - but they all seem to have more functionality then I desire - thus more costly.

Any ideas would be welcome !

 

[duke37]

If the objects are non-conducting, then a tuned circuit will absorb energy at its resonant frequency. Placing such a tuned circiut near a micro transmitter will affect the output which can be detected. Look up grid dip meter.

 

[donkey]

from the area i work in(security) i can tell you the rfid itself is a a loop of wire with what appears to be a small capacitor on it. the rfid requires no programming.
However the reciever does. it has to know what frequency YOUR rfid's are to enable, in your case, a light to flash.
I met a guy recently and the program he used was very simple. plug a laptop to the reciever, wave the card, set access (you will not have to do much here, just one layer of access- the light), save changes, and he was done. 100 cards took him 30 minutes, and each was a different code.
there are premade kits and then diy kits. depending on how many tags you want.
there are also small versions of the "posts" you see at supermarkets, the ones that buzz when you walk through them and one of your items has the security device still attached. maybe you could put one of the devices on your counter to detect the items.

 

[davenn]

RFID or optical (camera and object recognition) are still you only real practical choices as suggested to you in the other forum you posted in

Dave

 

[poor mystic]

I quite like the grid-dip idea (resonant coupling detection) myself. Of course it's got its limitations - the objects would need to be placed within the range of the sensing coil - but with ingenuity and patience I think it could work. After all the sensing coil could be quite large.