More LED's - Again

To All:

The steady decline in the cost of ultra-bright green LED's (now about
two-bits each for a 100-piece baggie) has generated renewed interest in
the bug-eyed LED nav lights I described on this Newsgroup a couple of
years ago.

Unfortunately, that renewed interest has lead to some renewed problems,
one having to do with the lay-out of the circuit board, the other with
its fabrication. But the most serious problem has to do with the fact
that ham radio operators learn to solder shortly after birth, or even
before... according to some. Along with the ability to solder is the
companion knowledge of how to make a circuit board out of a bit of
substrate and a piece of string about... that long. But the main
stumbling block for non-hams appears to be how to make all those
teenie-tiny holes in the circuit board.

MAKING HOLES

It's pretty easy. You need a tiny drill -- somewhere between #70 and
#75. Then you need to spin it about 12,000 rpm. And you need to keep
it perfectly vertical as you make the hole.

The drill bits are no problem. Harbor Freight will sell you a
selection of solid carbide bits suitable for the task; simply pick a
size to suit the components you're using, such as the wire legs of an
LED or quarter-watt resister.

A Dremel tool (or similar) is the handiest means of chucking the tiny
drill, most of which have a shank diameter of 1/8".

To hold it perfectly vertical you don't 'hold' it at all -- you make up
a 90 degree bracket and clamp, wire or glue the tool to the vertical
leg. On the horizontal leg you drill a 1/4" hole to accept a bolt
which you then chuck into your DRILL PRESS. There's a few picky-bits
to this method, such as using a bracket that is a true 90, and thick
enough so as not to deflect as you run the quill of your drill press up
& down. You need some method of preventing the quill from rotating of
course -- I use a simple wedge between the quill pulley and the frame
of the drill press head (big, old Craftsman floor model. Your mileage
may vary...) To keep from ruining the chuck in your drill press (which
was not designed to grab hold of threaded bolts) you put a barrel-nut
on the bolt.

Deal with all the tricky bits and the result is a shake-free,
carbide-tipped hole-maker that will give you a life-time of accurate
service (and already has, in my case... I used it to make the boards
for my first computer back in the mid-70's).

ELEVATION vs AZIMUTH

Azimuth is relative to the horizontal. Elevation means over-head. In
laying out the circuit board, asimuth is taken care of by orienting the
legs of the LED's. Since the LED's have an average viewing angle of 25
degrees, to provide adequate coverage the azimuth angle starts at 10
degrees and progresses in 20 degree increments. Of course, when you're
trying to provide full coverage across a segment of a sphere, your
LED's must be accurately oriented in TWO dimensions.

The key point here is that I chose to build the aximuth angle into the
circuit board.

The elevation angle is bent into the legs of the LED's using a simple
form-block, accurately printed via DeltaCAD, glued to a bit of plywood
and sanded to the line. To keep things simple, I abandoned the
variable height arrangement as described in my original post, other
than allowing a bit of overlap between one row of LED's to the next so
as to keep down the circuit board, which comes out about two by two
inches.

As a further simplification, I eliminated the left vs right bending
angles used in my original (2002) lights. Now all of the LED's get the
same set of bends relative to their positive lead. To accommodate the
change from left- to right-facing, I re-drew the circuit board.

MAKING THE CIRCUIT BOARD

The Old Fashioned Way was to start with a drawing then go to litho
film, then to a fine-meshed silk screen. Once you had the silk screen
you could whip out a hundred circuit boards in an afternoon... after
spending a month to arrive at that point.

Nowadays I simply print the circuit board mask onto cheap
glossy-finished color photo paper using a monochrome laser printer.
Here's why it works:

Laser printer media is a finely divided thermo-plastic -- a powder so
fine it is attracted to the electrostatic charge created by the laser.
The thermo-plastic material is transferred to the paper by heat.

This lends itself to making circuit boards because once the
thermo-plastic material has been transferred to the paper, it may be
RE-TRANSFERRED to the clean copper surface of a blank circuit board by
the application of ADDITIIONAL heat. In effect, you literally iron-on
the mask, solidly gluing the paper to the circuit board.

Now the trick is to get rid of the paper, which I'll get to in a
minute. But before I do, you should know that while using plain paper
is possible, the resulting transfer will show a lot of voids; plain
paper simply isn't a very good substrait for the thermo-plastic
material. But cheap color copier paper is. Color copier paper is
typically coated, giving it a denser, more uniform surface than regular
#20 bond. That slicker surface attracts a more uniform layer of the
thermo-plastic material; you end up with a dense, dark, void-free
pattern.

But it's gotta be CHEAP color copier paper because you want the stuff
to dissolve in warm, soapy water. High quality color copier paper is
some very tough stuff; it doesn't like to come apart. But the paper
HAS to come apart if we want to leave ONLY the thermo-plastic material
bonded to our circuit board. So use the cheap stuff. And soak it in
warm soapy water. Then scrub it with a tooth brush or whatever -- get
ALL of the paper off of the thermo-plastic.

Now you can etch the board in the usual way. And having etched it, you
gotta drill those zillion holes. Once etched & drilled, remove the
thermo-plastic, which you can do with MEK or other kidney-killer
solvent and a bit of steel wool.

The result is a bright copper circuit board, ready to accept components
and easy to solder. Once things are soldered and checked and and all
the errors corrected, give the thing a coating of clear finger-nail
polish (!) and you're all done -- a super bright nav light that will
never burn out (at least, not in your life time) that draws about a
quarter of an amp, meaning the wiring can be slightly smaller than a
starter cable.

-R.S.Hoover
-(KA6HZF)

PS -- Yes, you may have a copy of the circuit boards, if you wish. But
you could probably do better yourself -- except for the stern-light,
they're just rectangular 5x9 arrays. I don't have a web site and I
already get more email than I want so I'll try to find somewhere to
hang them. When I do, I post the information here... for all 385
subscribers of r.a.h. to read :-)