Hi. I build several arduino things but I really don't know how to tackle this project.
I would like to know the distance between a "reader" (arduino uno or other) and several objects.
If one object leaves >1meter, the reader will take some action. I would like to use it on many objects so if it could be small and cheap...
I don't need to know the position of objects, no triangulation or so...
I searched a lot on this forum and Internet and that's the "solutions" I founded :
- Passive RFID : Impossible because I can't get the (even approximate) distance of an object. Moreover, operating distance in theory cand be some meters, in fact it's < 10cm (or more with really big and not cheap readers)
- Active RFID : Seems to work but with several objects, the reader will have collision problems while reading the closest RFID tag and "not seeing" others. openbeacon active RFID seems to solve the problem but it is a bit complicated/big for this simple one-way thing I try to achieve
- Bluetooth : Would work. But big, complicated (bi-directional not needed) not cheap and I think it could not be powered by a tiny battery. But when I see this really small bluetooth many I'm wrong : http://iteadstudio.com/store/index.php?main_page=product_info&cPath=7&products_id=166
- Pulsing RF emitter : That's the solution which comes naturally to my mind. I imagine and RF emitter at 1khz, one a 2khz (fake values) etc... And the reader would know what object are here and their distance. But with this not-digital solution i fear the wave collisions (i'm not expert... at all).
(EDIT) New ideas :
- RF simple transmitter @ 433 or 315 Mhz like DCDW (thanks tkbyd) or Virtual Wire + some noise filters
- ZigBee or Nordic even if a little bit overkill it will be good prototype before RF transmitter
- DASH7 implementation (doesn't exist yet)
What is your opinion about this solutions ? Do you see something else ?