Wednesday, December 6, 2006
Psst! Hey, kid. You wanna cheap flasher?
L.E.D Flasher Kit, Catalog # LEDKIT $1.75 per kit
12VDC DPDT DIP RELAY, Catalog # RLY-420 $1.50 each.
SPDT 40 AMP RELAY, Catalog # RLY-415 $1.00 each
PN2222A NPN Transistor 5/$0.80
Couple of 1/4 Watt resisters, mebbe a nickel each.
The stuff above is available from All Electronics Corp., www.allelectronics.com
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I came across the LED flasher kit some years ago at a swap-meet, priced at less than the cost of the components. Being a cheapskate (and a ham radio operator) I bought a bunch.
The LED flasher kit consists of a postage-stamp-sized circuit board designed to accept a 555 IC plus a couple of discrete components. The circuit is wired as a basic timer. The discrete components - a couple of resisters and a capacitor - determine the on-off frequency and ratio of the timer's output. I used the kits to teach Cub Scouts and the like how to solder. (Put it together correctly, it'll wink at you :-)
The timer not only makes a good LED flasher, by changing the circuit just a tad it makes a nice oscillator for teaching Morse code. Or, you can fiddle with the circuit a bit more, replace the output LED with a transistor and toggle a DIP-size relay wired dead-bug to the other side of the circuit board. And while the pilot relay may be tiny, it can handle about two amps. That's enough to pick a BIG relay. Or half a dozen 30A relays. Or whatever. The 555 is an extremely versatile chip, its uses limited only by your imagination.
Why bother making up a flasher when you can buy one? I've been using ultra-bright LED's for running lights and the regular flasher wouldn't work with them because they draw so little current. (That's the running lights on a car, of course.) There are flashers that will work with low resistance circuits but they cost more than the home-brewed variety, usually flash at the wrong frequency and, in my experience, are less reliable.