Proximity detector circuit

[craigey1]

Hi all,

I was hoping someone might be able to help me with a little project. I'd like to build a small proximity detector that can detect (flash an led or beep etc) when a copy of the circuit is in a range of about 10M.

I know this would require a transmitter & reciever running continuously within the same circuit. I presume there would also need to be something that would tell it to ignore signals that are too strong, otherwise it would continuosly detect itself.

I was thinking a small bluetooth-type of device would do the job.

The idea is that a group of random people could each carry one with them, while they walk around in a public place & have to find each other. It's sort of a life based game where players chat online & so never actually see each other until the circuit tells them that another player is nearby.

Thanks in advance

 

[blueroomelectronics]

They sold those things in Japan several years ago.

 

[Darth Bagel]

Bluetooth seems like serious overkill for that application.

 

[Leftyretro]

Interesting application. I guess some form of time multiplexing where a given device listens for say 90% of the time and broadcasts for the other 10% of the time and they rely on the fact that the devices are not synchronized so messages are bound to get through in short order. 10 meters is not a demanding distance.

Not a lot of information has to pass between the devices, but a short FSK ascii message (send "HI") might help prevent false positives from interfering sources. A simple PIC with those cheap FSK transmitters/receiver modules might fill the bill. PIC turns on a cheap buzzer when it receives a valid message.

https://www.sparkfun.com/commerce/product_info.php?products_id=872


Lefty

 

[craigey1]

Brilliant. Thanks for that.

I was thinking a lot more about this last night.

For Instance it could use USB to charge a small rechargable battery & have an interface where you could enter your details & the details of who / what your looking for.
eg: I could enter my details as tall dark & handsome & I'm looking for a single tall blonde slim woman. One day I'd get a buzz from the device & would know that she is single, so I'd feel far more comfortable with asking her out. Alternatively she may get a buzz & notice Mr. TD&H.