my project is that... two objects are lying at a distance of 2 meters (not wired) if any of them is removed the other should start beeping ....and is it possible to put the third one also in the loop???all wireless ..

 

are they facing each other,you could use infra red leds,Bluetooth,rf.

 

I'm sure you could do this with bluetooth. Imagine 3 smartphones. If one stops transmitting or goes out of range, the other 2 can sound an alert.

 

are they facing each other,you could use infra red leds,Bluetooth,rf.

 

no, not necesserily facing each other

 

are they facing each other,you could use infra red leds,Bluetooth,rf.

 

not facing each other

 

At 2 meters, ultrasonic sound would be too directional. This is going to end up as an RF field.

 

could somebody help me with circuit using RF

 

Each device could transmit a unique identifier using IR through 360 degrees.

When any device "sees" another; it remembers the new devices identifier. If a device can no longer "see" a remembered device; it sounds an alarm and deletes it from memory.

You can have very many devices using this method (each device can monitor many other devices and each device is monitored by many other devices) and new devices can be added without requiring any modification of existing devices.

 

I bought a cheap, small transmitter/receiver pair that sends a carrier signal to trigger the receiver. They were good for about 50 feet with antennas and a few feet without. They seemed susceptible to interference, so I amplitude modulated the transmitter with a LM555, and detected the specific tone at the receiver with a LM567. That worked well. For your situation two pairs either at two different channels or two different tones. TxA and RxB are on object #1. TxB and RxA are on object #2. As long as the Rx on the object receives a signal, it is quiet. If the other object is moved out of range both objects sounds an alarm.
For three objects a similar three link loop:
TxA and RxB are on object #1
TxB and RxC are on object #2
TxC and RxA are on object #3
If #1 is moved, #3 looses its received signal, it sounds an alarm, and shuts off its transmitter. That causes RxC on object #2 to loose its received signal, sounds its alarm, and shuts off its transmitter. That then causes RxC on object #1 to loose its received signal, sound its alarm, and shut off its transmitter. But it was already alarming because it was out of range.

Ken

 

I was thinking of a carrier wave of some amplitude, with a different frequency for each object. Receive, and add an AGC circuit. Use a button when placing the objects as a command to access and store the AGC level. Big change in AGC level = trigger the alarm.

 

my project is that... two objects are lying at a distance of 2 meters (not wired) if any of them is removed the other should start beeping ....and is it possible to put the third one also in the loop???all wireless ..

What does it mean to be "removed"? If I move it so that it is 3m away, does that qualify?

Can other things in the environment change? If they are 2m apart, then someone could part a small car between them. Do they still need to know that the other is still there?

 

Do you max out at three object? Might you add a fourth or a fifth at some point? If you do, are you willing to modify all of the existing objects to accommodate each new object?

 

What does it mean to be "removed"? If I move it so that it is 3m away, does that qualify?

Can other things in the environment change? If they are 2m apart, then someone could part a small car between them. Do they still need to know that the other is still there?

if the distance is more than 2 meters there should be a beeping sound
there could be things between them it should work in the same way

 

Do you max out at three object? Might you add a fourth or a fifth at some point? If you do, are you willing to modify all of the existing objects to accommodate each new object?

yes

 

if the distance is more than 2 meters there should be a beeping sound
there could be things between them it should work in the same way

Uh oh, I think that means it needs to estimate actual distance, as opposed to merely detect a signal in range or not. Much trickier.

 

if the distance is more than 2 meters there should be a beeping sound
there could be things between them it should work in the same way

So that rules out a LOT of techniques. You can't rely on signal strength at all since that is going to vary due to all kinds of things even if the objects remain stationary. And if you need to tell the difference between something being 2 meters away and, say, 2.1 meters away, then you have a much more challenging task.

 

yes

I asked (that you quoted) three questions. A single "yes" tells me nothing since a Yes to the first question is very, very different than a Yes to the third.

 

I think dinoda has painted himself into a corner. Just because you can imagine it doesn't make it feasible. The way this is going, you will need a GPS receiver on each object and as far as I can tell, even those are only accurate to 1.34 inches. How much money are you willing to pay for this?