what thing could make an item open by just coming near to it?

I'm trying to make a necklace that lights up when i come near to it...
My plan is to attach a LED to a small glass ball and give it to my wife so that when i'm near it lights up.

I thought of a remote that uses Bluetooth although i don't think a receiver can fit to a simple necklace, and i actually don't have any idea how to make a remote.

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Re-design7 years ago
It would take some fiddling to make it work, but.

If you took on of the better transmitters for and r/c car and put that is as small a package as possible.  Replace the antenna with a wire that is a tuned length for the frequency of the radio.  That wire would be hidden under your shirt.  You need to know the freq. of the radio to be able to cut an antenna the right size for the transmitter.  You want it to broadcast maximum power.

Now, the necklace is the receiver but instead of having a speaker you will have an led indicator.  The necklace chain is the antenna and it would help if is were a perfect fraction of the frequency.  The antenna leads to a very simple diode receiver and transistor that acts like a switch turning an led on and off.  I would help if your wife is kinda geeky and likes technical jewelry made out of electronic stuff.

I'm sure that you could get all this to work but like I said it'll take some fiddling around before it does.  What should make it work is having a transistor sensitive enough to turn on from the power detected by the diode connected to the antenna.  You could adjust it so that it would only turn on when you are 2'-3' away if you were lucky.  The more powerful the transmitter was in the beginning the easier it will be to get it to work.

Unless you live right under the antenna farm of a radio station you should not have any problem with am/fm/tv setting off your proximity sensor early.

You can work on the receiver with a "borrowed" transmitter and not alter the tx. until you have the rx. working.  Then modify the antenna and then "miniaturize" the tx.
secretsecret (author)  Re-design7 years ago
Thanks for the idea.
How about hacking a toy walky talky?

Is it a good idea, would it have a wider coverage distance?
mwrenfro7 years ago

Depending on budget, you might adapt these shirts from Thinkgeek. But yeah, low power radio on any unlicensed (and available) frequency would be the way to go.
secretsecret (author)  mwrenfro7 years ago
Thanks for the link. That was very similar in concept.

do anyone know how that shirt was made?
is there any instructables available?
orksecurity7 years ago
Maybe https://secure.wikimedia.org/wikipedia/en/wiki/Personal_area_network ... but I don't know whether cheap/compact homebrew versions exist.
jeff-o7 years ago
I think anything RF-based would be too bulky. But maybe IR would work. An 8 pin microcontroller can run from a button cell battery, and combined with an IR transistor and the LED, would be pretty much all you need.

The microcontroller would periodically "wake up" and look for a specific IR code sent by a transmitter that you're wearing. If it detects a signal, it lights the LED.

The only catch? It would be line-of-sight only.
NachoMahma7 years ago
lemonie7 years ago

I was thinking of magnetism & a reed-type switch, but you'd have to get very near.
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