Sensing objects in a 2 meter radius

Hello, I'm trying to sense if certain objects are in a 2 meter radius from my arduino. The only data that needs to be send is an identification of the object (a number).

The first thing I thought was using RFIDs, a tag in the object and a RFID reader connected to the arduino. Never got to figure out how to do this a I found out that the RFID reader that I need costs more than 2 thousand dollars (at least in my country) and that is way out of my budget.

My second idea was using bluetooth modules on the objects and sensing their names in my arduino (with another module). I will have to figure out how to decrease the range of the bluetooth module in the arduino to 2 meters.

My question is: do I need a microcontroller for every bluetooth module (object) or can I establish their names with one microcontroller and then place the modules alone on the objects with a power supply? (Trying to have the lowest cost possible) Bear in mind that I'm new to arduino but I'm eager to learn.

If anyone has another idea to do this I would love to hear about it. Remember that I do not need to know the orientation of the object nor the exact distance from the arduino, just if it is inside a 2 meter radius and it's identification number.

Thanks in advance for your time and knowledge, Leo.

You will never be able to restrict any radio system to a short range like this. I don't know if you have a solvable problem.

Ok thanks Mike, but can you help me with the questions I asked about the bluetooth modules?

My question is: do I need a microcontroller for every bluetooth module (object) or can I establish their names with one microcontroller and then place the modules alone on the objects with a power supply? (Trying to have the lowest cost possible) Bear in mind that I'm new to arduino but I'm eager to learn.

Also I found this tutorial that shows how to increase the bluetooth range by scraping off the antenna from a bluetooth dongle and then adding a much bigger one. http://www.instructables.com/id/Increase-and-extend-the-range-of-a-USB-Bluetooth-d/?lang=es Maybe I can scrape some part of the antenna in order to reduce the range of the bluetooth module. As I said I'm new to this, I'm actually a medicine student who is doing this just for fun! Once again thanks in advance for your time and knowledge, Leo.

With the right software you can connect to multiple blue tooth devices, but I have little experience with it. However I have used radio a lot and you will find that reflections from nearby objects make it impossible to set an exact range. There will be direction sensitivity no matter what you try to do. If scraping paint off increases the range then putting paint on might decrease it. But it is so hit and miss as not to be worth bothering with. I would be interested to know what RFID system has a 2 meter omnidirectional range. I used to design RFID readers and it makes little sense to me.

I have no idea Mike, I looked for places in my country (Uruguay) that sell RFID systems and they said that something like what I need costs more than 2 thousand dollars and that's when I stop researching RFIDs.

For what I read a bluetooth master can connect with up to 7 seven slaves and each slave can only have 1 master. But I do not need them to connect or even pair, I just want to find if they are nearby. That's why I am trying to know if I need every bluetooth module connected to a microcontroller as there is no data that I want to process or send apart from their id.

that sell RFID systems and they said that something like what I need costs more than 2 thousand dollars and that's when I stop researching RFIDs.

Oh a bullshit answer.

Mobile phones can scan for nearby bluetooth modules without connecting to them so you should be able to do the same thing with an Arduino and a BT module. Look at the examples and see if there is a scan sketch, I know there is one for Wi-Fi shields.