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David Van Brink // Sun 2007.08.19 23:27 // {wbl weird blinking lights}

Beacon WBL

This next WBL is for a very specific purpose: finding one’s way home at night. It is of course intended for stationary deployment at an encampment in the flat, flat desert. It consists of 32 high brightness LEDs, in four groups of 8, blinking in patterns.

This was exciting, as I finally got to use a “transistor” in a project. Long ago, Dolphin (a man of many talents & avocations, but, alas, no public web presence) sent me some doodles explaining how to blink lots of LEDs from a pic chip.

                           (12V)            (5V)   
 +-[- Car Battery +]-[FUSE]-+-[5V regulator]--[V+   PIC*  Out   V-]---RTN
 |                          |        |                      |
RTN                         |       RTN                     |
             +--[10u Tant]--+                               > Rb = 220, 1/4W
             |              +-VVVVV-->|-->|-->|--+          > (~3.5V total 
            RTN             |                    |          > drop at 15mA)
                            +-VVVVV-->|-->|-->|--+          |
                            |                    |          |
                            +-VVVVV-->|-->|-->|--+        __b__
                                                 |         / \
                                                 +------c-/   V-e-----RTN

Ah, we don’t illustrate like that any more, hmm?

I implemented his circuit. Radio Shack had a packet with 15 “2n2222-like transistors” for a buck or two; it had 2n2222’s, 2n4401’s, and 2n3904’s in it. They all seem to work the same, in this application. I assembled the circuit shown below, except with the transistor driver duplicated four times attached to the PIC12F509.

And here’s the beacon, running happily, if not for very long, on a 9v battery. The picture doesn’t really express how bright the thing is. Piercing. I set it on the driveway and it was impressively bright from a block away. I bet it will be visible for a mile or more on the playa. A car battery will be able to power it for about a month of evenings…

The nifty modules are sold by Sure Electronics on eBay for $3 including shipping from China. Look for “Fantastic High Brightness LED Cluster”. Just add 9 or 12 volts straight in.

oh, i dont know. what do you think?

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