How To Make An Arrow Pointer

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How To Make An Arrow Pointer
Are you tired of pointing to stars with just a
little red dot?
Do you remember the days before laser pointers?
Have you seen the new super bright Light
Emitting Diodes?
If your answer is YES to any of these questions,
then this workshop is for you!
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The first version of an arrow pointer I made,
used this L.E.D. flashlight. It was seen at the
IPS meeting in Wichita, Kansas.
If you want to make this pointer, you can
download instructions from my web
page. www.pa.msu.edu/people/frenchj
In this newer design, you will make your own LED
flashlight which is specialized for use as a
pointer.
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The first thing you will need is a superbright
Light Emitting Diode
A good place to get LEDs are the internet. I
bought some from superbrightleds.com Their
prices are good and they ship fast.
The brightness or intensity of leds are
measured in millicandela (mcd). Get one rated
over 10,000 mcd. Superbright red ones are 12,000
mcd Superbright Yellows are 10,000
mcd Superbright Whites are 18,000 mcd
White leds are 1.59, Reds and Yellows are only
62.
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Next, get some plumbing parts
A plastic PVC tailpiece will be the body of your
flashlight. You can use one without threads for a
sleeker look, or a threaded one if you want to be
able to lock in the focus.
A six inch long 1½ inch extension tube (aka,
tailpiece) will be used to hold the lens in place
over the arrow slide and LED. Get the kind with
threads and a big nut on the end to hold the
lens
You can get these at you local hardware store for
about 2.00 each.
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and a lens.
This 5 inch Ektanar lens came from a Kodak slide
projector.
I scavenged this lens from an old single slide
projector.
This lens is a Cabin 75 mm focal length lens.
This powerpoint shows how make a pointer using
the Cabin lens. Its a bit different if you use
another lens, but still easy.
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Get some wire, a switch, a resistor, a 9 volt
battery clip, heat shrink tubing and a 35mm film
can and an extra film can lid.
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Youll need a few tools too. Get a multimeter,
soldering iron, solder, Exacto knife, black tape,
drill and a Dremel tool or saw.
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Heres a quick sketch of whats in the pointer
and how it goes together.
Note This was not drawn on Professor Whoopees
3D-BB, Chumley! (Bonus points for anyone that
knows what cartoon featured the 3D-BB)
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The wiring schematic for the pointer looks like
this.
Switch
Resistor
Battery
Diode
Diodes have a and lead. If its in backwards
it wont light up.
Its important to find the correct value for the
resistor.
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The key is to use a resistor that will limit the
current in the diode to 20 milliamps. Light
Emitting Diodes typically shine brightest at 20
mA of current. More current than 20 mA can burn
out the diode or shorten its lifetime. At less
current, it wont be as bright. Set the
multimeter to measure milliAmps and measure the
current as you try different resistors. Try and
get as close to 20 without going over.
A small breadboard (socket board) is useful for
testing. But alligator clips will work too.
Start with larger resistors and work your way down
Or just go with 330 ohms and call it good!
There are resistor value calculators available on
the web that can tell you the resistor you will
need for a particular voltage and current. Look
at http//linear1.org/ckts/led.php as an example.
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Make an arrow using your favorite graphics
program
and turn it into a slide.
Or download some of these arrows from my web site.
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When you have all the parts, its time to put it
all together.

• Parts List
• LED
• Lens
• 2 Extension tubes
• Arrow Slide
• Black Foil or Tape
• Film can w/extra lid
• Dremel Tool
• Safety Glasses

• Drill
• Solder
• Soldering iron
• Switch
• Resistor
• 9 volt battery
• Battery clip
• Heat shrink tube

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Solder the circuit.
Put the diode and resistor in series. Cover all
open leads with heat shrink tubing. Connect the
switch. Use a heat sink when soldering the diode.
Too much heat can damage the diode.
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Drill a hole in the side for the switch.
Stick the wires, diode and switch into the
extension tube.
Some switches have the nut on the outside and
some have it on the inside. If the nut is on the
inside, you will need to fit it through the hole
before it is soldered together. If the nut for
the switch in on the outside, it is easier to
install.
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Cut the film can to hold the LED in the center of
the barrel of the tube.
Remove the bottom of the can and cut a notch out
for the wires and switch.
Cut or drill a hole for the LED.
Stick the LED in the hole.
Radio Shack sells little grommets for holding
LEDs. Use one if you want it to look pretty!
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Stick the can with LED and wires into the
extension tube.
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Put in your arrow slide
Cut another hole in the second lid and tape your
arrow over the hole
Put this film holder lid over the LED. Line it
up so the LED shines through the arrow.
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Install the lens Ream out the top of the
extension tube so the lens will fit in the top.
Before
After
This step will get messy as the bits of plastic
fly!
Use the meanest looking gouger for the Dremel
Tool.
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Determine the distance from the slide to the lens.
Go into the planetarium dome. Hold the lens
over the flashlight and focus the arrow onto the
dome.
Measure the distance between the flashlight and
lens. This will tell you where to cut the
extension tube.
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Cut the extension tube to the proper length.
Be sure to wear safety glasses when using a
Dremel tool.
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Put the lens in the extension tube and carefully
screw on the top.
Insert some black foil into the extension tube to
reduce internal reflections. You can also use
black masking tape.
A very important step.
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Put the lens/extension tube into the focus collar
and insert it into your flashlight.
Slide the lens back and forth until its focused.
Point to the stars! Youre done.
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This pointer design was inspired by a pointer
first made by Tom Ferguson, an electrical
engineering graduate from Michigan State
University and former planetarium staff member of
the Abrams Planetarium. His first pointer used a
Mag-light flashlight as the light source. We then
switched to the Brinkman LED flashlight. Now
this one is independent of any store bought
flashlight.
Here we see Tom using his pointer to vanquish his
foes!
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For more information visit John Frenchs web site
at http//www.pa.msu.edu/people/frenchj Here you
can download arrow jegs, this pointer
powerpoint, the older pointer powerpoint and even
link to my fascinating Moist Towelette Museum web
page, which has nothing to do with this pointer.
(That was just a cheap plug for my moist
towelette museum!)
Presented by John French Planetarium
Production Coordinator Abrams Planetarium Michig
an State University frenchj_at_msu.edu