Miniature RF Communications Circuitry

[newsoms]

I am working on school project with my daughter, and we conceived of an idea to sort of help locate personal devices in the same way that cordless phones have the ability to press a "locate handset" button on the phone base to make the lost handset start ringing. So i am curious if someone can point me to some simple design for a capability like this. I am also wondering if bluetooth could be a good communication choice so that my "base unit" could be a PDA, computer or other device that can send a message over bluetooth to the lost device and tell it to start beeping. The device unit will need to be as small as possible, so i was thinking of some sort of watch battery and a miniature speaker and of course some sort of RF/bluetooth receiver circuit.

I have not been involved in circuit design since my college days back in 1985 so looking for just simple descriptions here. Thanks for any help!

 

[(*steve*)]

I suspect that you could build a proof of concept device somewhat larger than you would want in reality.

Basically all you need is a transmitter and a separate receiver that sounds an alert when an appropriate signal is received.

To conserve power you might only turn the receiver on for say a quarter of a second every 5 seconds or so.

You could use a microcontroller to decode the received signal for some special pattern that indicates it should activate. The transmitter should broadcast this continuously for at least (say) 5 seconds when the transmit button is pressed so that it can guarantee that any/all devices set up to receive this signal will have awoken during that time.

 

[newsoms]

I like the power saving approach; great idea. How small do you think i could get this sort of logic? Also, do you have any idea how much it might cost in parts (i.e. <$3? or <$5, etc.)?

Thanks

 

[(*steve*)]

I would do all the smarts in a microcontroller. You may get away with an 8 pin device. The receiver would be the largest single part (aside from the battery perhaps).

But you do have to learn to program the microcontroller...

Have a look at PicAXE chips. Relatively cheap ($5?) and easy/cheap to program.

 

[davenn]

parts cost all up, maybe $50 - 70, maybe more, depending on what TX and RX modules you can source on say eBay for a good price.

your transmitter (TX) and receiver (RX) are going to have to be coded, else the receiver will respond to every other transmitter on or near the freq of use. and it will be beeping often and draining the battery needlessly apart from drivinig you nutz with the beeping

Dave