Challenge on how to build 2 devices to detect eachother

[bright_ideas]

Hi all,

I am a NOOB electronics guy but can do anything once told/shown how to. Thing is I have all these ideas running around in my head but not enough knowledge on how to put it together?!?

I want to create the following:

• Two devices that each fit onto a wearable bands of some sort
• Must be as small as possible, say 30mmx20mmx10mm
• Must be able to detect the other device when no line of sight
• Both devices should emit a high pitch sound when they detect each others presence
• MUST have a detection range limited to between 40cm-200cm
• Should have a re-chargeable battery life of 3 days or more
• Device should be able to be set or locked to each other and not influenced by another pair nearby.

Any help much appreciated.

Thanks all

[mariush]

First thing I've thought about is an Arduino and a Bluetooth shield

http://www.makershed.com/BTLE_Arduino_Shield_p/mkrbl1.htm
http://www.amazon.com/Bluetooth-Shield-for-Arduino/dp/B007BYI172

If you remove the non-essential stuff like the pins on the side and put components on both sides of pcb you can probably shrink it a lot , enough to fit your requirements. An arduino can also be shrinked a lot and you could stack the boards ... the battery can be a li-polymer or li-ion hidden in the strap used to attach the device on hand.

Another idea would be to maybe make the device emit an ultrasonic sound, above the human hearing, which would be loud enough to be heard for 2 meters and not distorted by small obstacles (but walls would probably block the sound)

[bright_ideas]

Thanks for that suggestion but my review of those links and products seems to big for 30mmx20mmx10mm

[mariush]

Well of course they're big, but that's only because the Arduino is a standardized sizee, required to expose all those pins on the side with a standardized connector, with 0.1" pitch (2.54mm)

It's unlikely you're going to find something ready made in that format, but you can get the pcb layout for arduino (it's open source hardware I think) and remove everything you don't need.  Just the same, you can get one of those bluetooth modules and redesign it to fit in the size you want.

If you're a complete beginner, naturally this is not for you...

I didn't say buy them, I said inspire yourself from them and make your own, or hire someone to do it for you.

[bright_ideas]

Thanks I see your intention now with your suggestions. I am a electronics noob so I guess I will try and do this myself as you suggest but if not hire someone.

Thanks again

[Smokey]

check out the TI Chronos watch.
http://www.ti.com/tool/ez430-chronos&DCMP=Chronos&HQS=Other+OT+chronos

Depending on how much other stuff you plan on programming this thing to to, you might be able to take the band off the watch and just use it directly in your project.

[bright_ideas]

WOW! Very cool. Thx. But waaay to much for what I need :-) I need only maybe only 2 of the functions.

[TerminalJack505]

Sounds like you need a microcontroller with a built in RF transceiver.  Or maybe a microcontroller with a separate transceiver IC. 

I'm no RF expert but I'm guessing one of the biggest factors in choosing is going to be the frequency band you use.  The authorities don't want you using just any frequency.

[bright_ideas]

Yes quite right and they have recently changed them but I do have those at hand actually due to another unrelated GPS product.

[smashedProton]

Guys.. you are really making things way too complicated.  Bluetooth is entirely unnecessary.  I made you a block diagram of what you need to do.  Its a simple rf circuit.  you could use a sa602a for the reference oscillator and multiplier.

[bright_ideas]

WOW again! Finally someone who came up a possible simple solution for this noob(me). THanks smashedProton.

Now for this noob to figure that diagram out and hope it meets all my points above. Some hints plzzz...

Thanks

[smashedProton]

afrotechmods, w2aww, wikipedia, art of electronics

[bright_ideas]

great. thx again

[TerminalJack505]

If you decide to create your own transceiver from discrete parts then another good website is talking electronics.  There are a ton of RF circuits and explanations.

[bright_ideas]

Thanks TerminalJack I will look at this to and post updates here for you guys as I progress, or not :-)

[G7PSK]

The distances you are talking about would suggest that you look into near field devices.

[bright_ideas]

Well i guess nearer than farther. "Near field" like in RFID? as I have not found one yet that does over 20cm range.

[TerminalJack505]

Keep in mind too that a lot of the RF transceiver ICs have selectable transmission power. 

You can buy microcontrollers with built-in RF transceivers for less than $5 each.

If I were you and I wanted to get this project off the ground I would buy one of the vendor's RF evaluation/development kits and basically just use their reference design pretty much as-is.  Their design will likely have a huge antenna and a bunch of stuff you won't need but they'll likely have 80% of what you will need in your design already done.

I'd start my search right here.