Looking for inexpensive
I want to have a single stationary circuit that detects the presence of objects on my kitchen counter top. The objects would have some sort of device mounted on them and when placed on the counter, the detector would flash an led.
Any sort of photo interrupter / light beam blocker type system is totally unworkable and is out of the question. The actual objects are not important.
So, something like using an rfid sensor for the detector and rfid tags attached to the various objects. RFID may be a bit too complicated as I don?t care to distinguish between the objects.
Is there any cheap module that is used like RFID but does involve detecting an objects ID ?
rfid is the way to go. You can buy off the shelf tags and stick them on the iterms. You can buy, or build your own, reader. The only question is how much range you need, and if you can get by with passive (vs. battery operated active) tags.
Would'nt I then need an RFID programmer ? All of them would be the same - I do not wish to tell objects apart - only their presence. Distance would be less then 10 feet.
You need to distinguish each objects existence in a cheap RF project. Identical units will make it much more complicated to detect presence of one or many objects. For identical units, there are some possibilities to detect variations in RF field due to that a secondary antenna is moves around and causes phase shift, but it is very expensive and would not allow any else movement in the kitchen.
RFID can be bought programmed with unique id. It is still not a simple task as cheap RFID equipment have short coverage distance.
A much simpler task had been to use similar theft protection that is used in many shops at exit. A loop antenna covering kitchen door and checks for harmonics.
A cheap web cam is within your budget, write a software that compare with an previous picture if something have changed on your counter top and identify it by optical recognition.
The most simple RFID tags have just an unique serial number and don't need any programming. Passive tags at 3 m are basically feasible with the ISO 15693 13.56 MHz standard, but requiring large reader coils and a respective power amplifier, so the 50 S budget will be most likely exceeded. But that won't be better with any RFID or EAS (electronic article surveillance) technology at this distance.
The other point is, that RFID can't sense an exact position, if the objects are actually on the kitchen counter top, or e.g. hidden in a drawer. Your specification isn't clear in this regard. (The only clear point is about light beam "unworkable", without telling why). The image recognition solution would be perfect in position detection.