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Keychain IR beacon Answered

What do you think about a IR beacon on a keychain that flashes every 10 secs or so while its not moving. (And optionally flash brightly before going into energy saving mode turns when touched) essentially you can use your mobile phone to locate your keys when lost.


You know of those keychain-finder devices, where you clap or whistle and they respond with a beep so you can find them?  Find some way to replace the speaker with an IR LED ( or just tie in the IR LED so you have both visual and audible locating.)

That would be pretty cool... I'm thinking it could be done either with a microcontroller or with 2 555 timers, one in monostable and one in astable, a vibration switch as a trigger and a couple of IR LED's as the source of IR.

That is what irritates me about the LED flasher ic becoming nearly extinct. It used so much less current then the 555 *sigh*

Ah you mean the good old transistor and cap ones, I used them loads in school as 555's were pretty scarce and I still think that overall they're a better circuit that seems to screw up about 90% less than 555's in ameteur circuit building, also they can drive more LED's than an IC and it's a pretty compact circuit. not tiny but good.

Well, I was referring to the LM3909 really. It was a really cool (hobbyist) useful IC, but industry demands were kind of low.

Oh right, well we did used to have a fair few of them kicking about the school but they were rarely used because the techie knew they were in short supplies so he refused to let us have them.

Yeah, back when I had opportunity to get a few hundred, I should have......sell em for $10 a piece now LOL. I wouldn't REALLY do that, but they WOULD be handy to have around

I can't work with surface mount stuff, but even so, fitting all that into the space of an 8 pin DIP IC would be difficult and getting the specs just right might be cumbersome. But, on the plus side, you could fine tune it the way you wanted to. :-)

there are transistor driven led flasher circuits out there.

Yes, but the LM3909 was so simple and elegant a solution and was so useful to hobbyists, it is sad it is now hard to find.

It made puny, dim flashes, though. About what you'd expect from discharging a 300uF cap though a resistor an LED; it had a huge battery life because there was so little energy in each flash. I bet you could get almost the same battery life out of a modern microcontroller, though you might lose the 1.5V capability.

Hmm, it is hard to remember back to the days I had a bunch (and I may still have a few....I will have to dig a bit) but I had a few decent circuits from them (not just LED circuits) :-)

an Infrared beacon? I am lost as to how this helps find the keys.

I think the idea is that you use a digital camera or mobile phone camera to detect the infra red light emitting from the lost keys.

Digital cameras can pick up the light from an IR LED with ease, try pointing your TV remote at a webcam.

COOL ! I didn't know that, both my CAM and my camera (the CAM is better at it). That is REALLY handy to know, thanks.

Wow, even my Phone's digital camera sees it.

Cool! Idea! I don't know how to build it though.