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I want to make some objects that will know when they are, let's say, 3 feet(or less) from each other.

They need to also know the identification of the objects close to them.

For example. If object Ball is in presence of a Cube, they would both be 'unhappy'. But if a Ball is in the presence of another Ball. They would both be 'happy'.

Summing up...I'm looking for cheap ways to have objects: (1) know when others are around (2) know their unique ID (which would probably require some sort of broadcasting of IDs by each device)

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  • \$\begingroup\$ How accurate must you know the distance? If the Ball must no longer be happy when the other Ball is 4 feet distant, you will have a challenge. \$\endgroup\$ – Wouter van Ooijen Aug 31 '13 at 8:32
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    \$\begingroup\$ This question is way too broad. You might want to do some initial research yourself and then ask about few alternatives, or provide more information about the problem you're trying to solve to narrow down the options. You may also want to clarify what do you mean by "cheap technology": the cost of the components, or the cost of the time you'll have to spend in order to achieve your task with the suggested technology. \$\endgroup\$ – Vasiliy Aug 31 '13 at 9:25
  • \$\begingroup\$ what about RFID? \$\endgroup\$ – vrleboss Aug 31 '13 at 19:39
  • \$\begingroup\$ The prevalence of RFID makes it a good starting point. Active or passive? \$\endgroup\$ – Andyz Smith Sep 1 '13 at 2:46
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A cheap old fashioned way is by audio. Simply have a small speaker and microphone on each device. Different frequency for each ID, or use one frequency and have each device transmit an ID continuously after a pause of random length. Tiny millisecond long clicks at >20kHz will easily be enough and won't be audiable to humans.

You could even use volume to guestimate distance between them.

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There are countless cheap ways devices can wirelessly communicate! I particularly like SparkFun's Nike iPod dissection post! I'm so out of touch I wasn't even aware such a thing existed. Definitely look around in the arduino and robotics circles; those folks are all about cheap & easy wirelessness.

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You will need that all objects send and receive data identification about who is who. But you will have some problem, considering that you want to produce a cheap large scale product.

The cheaper to send and receiver is infrared, but you can´t have anything between the sender and receiver, and the distance you can try to calibrate but the distance will chance if change the light of environment, if two send their ID at same time will understand.

With radio this will be more expensive to project, can pass through somethings, but will have the same problem of who can talk now, that can be solve with a master that reach all objects and manage who can talk.

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Most logical solution is RFID, but it's certainly not cheap and their sensitivity range is pretty limited.

Cheapest method I can think of perhaps by using pair of infrared transmitter and receiver.

Choose transmitter with widest angle you can get — at least 120° — and put several parallel-tied transmitters and receivers on object's surface (make sure there's no blind spot).

Assign each object a unique ID. You can use encoder/decoder IC (such PT2262 / PT2272 pair) to simplify the identification process.

You can also give each object different broadcast interval to minimize interference.

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