Drafting a spiral?

[Charles Lind]

I need to draw a 32 turn spiral pattern, for a "pancake" coil antenna,
that will be suitable for etching PCB's. IOW clean edges and uniform
widths for the tracks and spacing. Diameter is approx 150mm. Can
anyone please suggest how to do this accurately, preferably by
computer?

Charles Lind

 

[Tim Williams]

I need to draw a 32 turn spiral pattern, for a "pancake" coil antenna,
that will be suitable for etching PCB's. IOW clean edges and uniform
widths for the tracks and spacing. Diameter is approx 150mm. Can
anyone please suggest how to do this accurately, preferably by
computer?

Parametrically, you want r(theta) = pitch * theta / 2pi, with theta =
(0, N * 2pi), N turns, for theta in radians. The centerline of the
trace follows this path, so you need to offset it (either side,
perpendicular to the path) by half the width to get the actual
profile. Then add caps on the endpoints to make a contiguous
perimeter.

If all you have are circles and splines, you might get away with
increasing radius semicircles joined end-to-end. It will look wrong,
but the overall effect will still be right.

Tim

 

[Joerg]

I need to draw a 32 turn spiral pattern, for a "pancake" coil antenna,
that will be suitable for etching PCB's. IOW clean edges and uniform
widths for the tracks and spacing. Diameter is approx 150mm. Can
anyone please suggest how to do this accurately, preferably by
computer?

Charles Lind

If this is for hobby or non-profit use: Cadsoft Eagle has a free version
that allows small circuit board sizes (but I guess you could zoom that
up with some other SW for the antenna if needed). Install that. Then
download "print-inductor.zip" from here:

http://www.cadsoft.de/cgi-bin/downl...ublic/download.htm.en&dir=eagle/userfiles/ulp

I have not used this particular download file myself but it should
unpack a *.ulp file (User Language Program) which creates spiral PCB
inductors. This ULP file needs to be copied into the same directory
where all the ULPs are that come standard with the software. File should
be safe and tested quite well, Mr.Zaffran is one of the engineers who
works at Cadsoft.

Try the schematic editor as well, maybe you like it.

 

[Archimedes' Lever]

I need to draw a 32 turn spiral pattern, for a "pancake" coil antenna,
that will be suitable for etching PCB's. IOW clean edges and uniform
widths for the tracks and spacing. Diameter is approx 150mm. Can
anyone please suggest how to do this accurately, preferably by
computer?

Charles Lind

You design a form on the computer that you can make in manufacturing.
The form is a cardboard (paperboard) helix that you print out, and roll
up onto a tube, so you can paste it onto a cardboard tube. The print job
prints the line of your antenna onto the paper. The finished tube has
lines on it now that you use a form for the positioning of the antenna
elements. Once everything is assembled, you remove the tube from within
the antenna, and all that is left is the antenna itself.

So the CAD design is for the printed helix before it gets rolled up onto
the tube form that is the diameter of your helix.

Done right, it will have your layout lines in all the right places so
that the antenna builders can build the antenna. Automated process can
be derived from similar fixtures and forms methods, but this antenna
style sounds difficult to automate too much.

 

[Ralph Barone]

You could probably do it using Postscript, which is actually
a powerful drawing language in its own right. An online
book probably has everything you need:

http://www.math.ubc.ca/~cass/graphics/text/www/index.html

old_x = 0
old_y = 0

for turns = 1 to 32
for theta = 0 to 359
r = (360 * turns + theta) / (150/32)
new_x = r * cos(theta)
new_y = r * sin(theta)
drawline (old_x, old_y, new_x, new_y)
old_x = new_x
old_y = new_y
end for
end for

or something like that...

 

[[email protected]]

I need to draw a 32 turn spiral pattern, for a "pancake" coil antenna,
that will be suitable for etching PCB's. IOW clean edges and uniform
widths for the tracks and spacing. Diameter is approx 150mm. Can
anyone please suggest how to do this accurately, preferably by
computer?

Charles Lind

It's a cheap but excellent PCB layout program that has spirals and
polygons built in. Set turns, track width, start radius,distance
http://www.abacom-online.de/uk/html/sprint-layout.html

 

[MooseFET]

I need to draw a 32 turn spiral pattern, for a "pancake" coil antenna,
that will be suitable for etching PCB's. IOW clean edges and uniform
widths for the tracks and spacing. Diameter is approx 150mm. Can
anyone please suggest how to do this accurately, preferably by
computer?

Others have suggested good ways to do the figuring of the spiral.
Making it into Gerber plots is another step.

The GEDA PCB program stores its PCB layout in an easy to understand
format. You can make your program produce the spiral in a file that
you can then copy and paste into the ASCII file that is the layout.
Then you can make Gerber plots. This way, you can do other parts too.

 

[linnix]

old_x = 0
old_y = 0

for turns = 1 to 32
for theta = 0 to 359
r = (360 * turns + theta) / (150/32)
new_x = r * cos(theta)
new_y = r * sin(theta)
drawline (old_x, old_y, new_x, new_y)
old_x = new_x
old_y = new_y
end for
end for

or something like that...

I think you want:
(turns + theta/360) * (150/32)

For gerbers:

MOVE(0,0); // D02
for turns = 1 to 32
for theta = 0 to 359
r = (turns + theta/360) * (150/32)
new_x = r * cos(theta)
new_y = r * sin(theta)
DRAW(new_x, new_y);
end for
end for