Long life flashing LED

October 21, 2006 7:39 AM

Any suggestions for a small, battery-powered flashing LED setup I can use for an outdoor mock alarm?

I have a faceplate I'd like to turn into a simple mock alarm system status indicator. Need a flashing LED bright enough to be seen from 20 yards, but either low enough power consumption that I can keep the thing flashing 24/7 for hopefully at least a year (before needing to change battery) or a circuit that somehow incorporates a simple evening timer or light sensitive switch. I'd like the whole setup to be as small as possible, and since I live in the Midwest, the power source needs to withstand zero degree temperatures. It's for a workshed that doesn't have any power, so I can't hardwire it to a real power supply.

Ideal would be:

- bright flashing LED
- smallest battery possible
- battery withstand cold
- longest lasting power setup possible
- photoelectric switch
- evening on/off timer

Greatly appreciate any suggestions!

Thanks.

posted by pallen123 to Technology (5 answers total)

Get thee to an electronics store, and tell the people behind the counter what you want to do. There are some pretty impressive batteries out there, and that combined with a simple weatherproof box and a blinking LED should do the trick.

A light sensitive switch should be easy enough. Again, the staff at an electronics store should be happy to help you get the right parts and tell you how to wire them.
posted by tomble at 7:57 AM on October 21, 2006

You could use adapt a red LED biking light. They run on batteries and are bright enough to be seen from faraway, and have different flashing modes.
posted by hooray at 8:53 AM on October 21, 2006

Get an LM3909 chip. It's an "LED flasher", very efficient and cheap, requiring only the LED and one or two external capacitors. With a single D-sized alkaline cell, it will work for more than a year. The datasheet contains example schematics that do what you want; google to find it.

Just remember to check the temperature range of your capacitors - some electrolytes can't be used in a cold environment.
posted by springload at 8:56 AM on October 21, 2006

You can buy LEDs with a flasher unit built in. One of them, an appropriate value resistor and a battery (lithium maybe? I'm no battery expert...) would do the job.

I have no idea what the sun is like where you live, but perhaps a small solar cell and using a rechargeable battery instead could extend the run time.

Personally, I would just leave the thing to run 24/7 to save on complications, though I understand this isn't what you asked!
posted by 999 at 9:22 AM on October 21, 2006

Agh, I can't find the part number, but I used to work at Radioshack, and there we sold a kit that does EXACTLY what you want. For about 15$ it comes as a little black box and the battery lasts about a year.

If you want a higher-intensity LED just buy the kit and solder in a higher-intensity LED.

If you don't find this device at RadioShack, just ask your local car stereo installer for a fake alarm. They'll be happy to sell you a 20$ kit with everything you need.
posted by fake at 12:07 PM on October 21, 2006