How would you like to talk over a laser beam?
In about 15 minutes you can set up your own laser communication system,
using cheap laser pen pointers and a few parts from Radio Shack.
For the transmitter you will need:
A battery holder that holds the same number of batteries as the
laser pointer (often 3 cells). The batteries can be any size,
but they must be the same voltage as the laser batteries. You
may need to get one that holds two cells, and another that holds
one cell, and wire them together in series. Radio Shack has a
A transistor radio. Later we will use a microphone and an amplifier
(Radio Shack #33-1067 and #277-1008),
but at first we will send your favorite radio station over the laser
An earphone jack that will fit your transistor radio
(Radio Shack #42-2434).
A transformer of the type known as an audio output transformer.
It consists of an 8 ohm coil and a 1000 ohm coil. The one I used is
the Radio Shack #273-1380. We now carry them
Some clip leads (wires with alligator clips on the ends) to
put it all together. At least one of the clip leads should be
the type with a long slender point (Radio Shack #278-016, #270-372, or
to connect to the inside of
the laser pointer. You can substitute regular wire and solder
if you like, but the clip leads are fast and simple. Radio Shack
has a wide selection of clip leads (such as ##270-378).
A two-lead bicolor light emitting diode, to protect the laser from
high voltage spikes.
For the receiver you will need:
A small solar cell (such as Radio Shack #276-124).
You may have to solder your own
wires to it if it doesn't come with wires attached.
A microphone jack that will fit the phono input of your stereo
(Radio Shack #42-2434 or ##42-2457).
Instead of a stereo, you can use the small amplifiers that
Radio Shack sells (#277-1008).
It may be hard to find a battery holder that holds three batteries. You can
use two battery holders (one that holds two batteries, and one that holds
a single battery) and connect them in series.
Remove any batteries from the laser.
Connect a clip lead to the inside of the laser pointer where the battery
touched. Usually there is a small spring to which you can attach the clip
lead. The other end of the battery usually connects to the case of the
laser. Since there are many different styles of laser pointer, you may have
to experiment with clip lead placement to get the laser to work with the
new external battery pack. You may also have to hold down the laser's
push button switch by wrapping a rubber band or some wire around it.
Test the connection
before you attach the transformer, to make sure the laser works with the new
battery pack. If it doesn't light, try reversing the battery. Battery
reversal will not harm the laser.
Connect the 1,000 ohm side of the transformer between the battery and
the laser. The 1,000 ohm side of the transformer has three wires
coming from it. We only use the outside two wires. The inside wire
is called a center tap and we do not use it in this circuit.
Connect the bicolor light emitting diode to the two outside wires
of the transformer on the 1,000 ohm side. We are using this part
(the bicolor LED) as a protection device to prevent the laser from
getting high voltage spikes from the transformer. We didn't need
to do this with the old-style lasers that had protection circuits
built into them, but there are a lot of lasers being sold lately
that have no protection, and need the bicolor LED to absorb any
extra high voltage the transformer may produce when it is connected
or disconnected. If you see the LED flash when you connect the
battery, you will be seeing it absorb a high voltage spike that
might have otherwise damaged the laser.
Test the laser by attaching the battery. The laser should
operate normally at this point.
Connect the earphone jack to the 8 ohm side of the transformer.
The schematic of the transmitter looks like this:
The transformer modulates the power going to the laser.
The signal from the radio
is added to and subtracted from the battery power, and the
laser gets brighter and dimmer along with the volume of the
music or voice in the signal.
The receiver is the simplest part. You simply connect the solar cell to the
microphone jack, and plug it into the amplifier or stereo phono input. It does
not matter which way the wires are connected to the solar cell.
Here is the schematic of the receiver:
For this project we have removed the laser assembly from a small
$10.00 laser pointer. The power supply circuit is the green board
attached to the brass laser head.
We carry similar laser pointers
our catalog that are easily disassembled for this project.
The laser below has voltage spike protection on the circuit board.
The one you get may not have this, and so you will want to put a
bicolor LED across the transformer like we did in the previous
The power supply circuit came conveniently marked with a plus and
a minus next to two holes in the board. We solder the black negative
lead from the battery clip to the hole marked minus. We solder one of
the 1000 ohm coil leads to the hole marked plus. We solder the red
positive lead of the battery clip to the other lead from the 1000 ohm
The battery clip is attached to a 4.5 volt battery pack (not
a 9 volt battery!). Since I didn't have a pack that takes 3 cells,
I used one that takes 4 AA batteries, and I replaced one of the four
batteries with a straight piece of bare wire.
That's it! We have a laser transmitter, in just a few minutes!
A new receiver
The solar cell receiver has some drawbacks. It is expensive
(solar cells are a few dollars each), and fragile.
A cheaper, sturdier alternative is to use a cadmium sulphide
photoresistor instead of the silicon photocell.
A cadmium sulphide photoresistor is shown below (magnified
many times). It does not produce electricity from light the way
the solar cell did. Instead, the light that falls on it changes its
resistance to electricity.
If we connect a battery and a photoresistor together, they can act
like the solar cell. As the intensity of the light changes, the
amount of electricity output changes in response.
The new receiver is very simple, and looks like this:
In all of the laser communicators on this page, the laser light
is amplitude modulated. This simply means that the amount
of light the laser emits varies over time.
To understand what is going on, it helps to consider how a
loudspeaker makes sound. A loudspeaker is a paper cone attached to a coil
of wire that sits in a magnetic field from a strong permanent magnet.
When an electric current flows in the loudspeaker coil,
the coil becomes an electromagnet,
and it moves toward or away from the permanent magnet. As it moves, the
paper cone pushes on the air around it, compressing the air in front of
it, and expanding the air behind it. Waves of compressed and expanded
air travel to your ear, and cause your eardrum to move in time to the
movements of the paper cone.
The laser communicator adds two components to the loudspeaker concept.
We take the electrical signal that goes to the loudspeaker, and connect
it instead to the laser, so the laser gets brighter and dimmer as the
electric current varies. The second component is the receiver, which
converts the light back into an electric current. This current varies
in time with the first current, because the amount of light that it
receives is varying in time.
This second electric current is used to move the paper cone of a
loudspeaker, just as before. However, now the loudspeaker can be
quite a distance away from the original electric current, without
any wires connecting the two.
Make your own 3D pictures in minutes
In this section you will see just how easy it is to take pictures
that show realistic three dimensional (3D) images.
The pictures can be viewed in three ways: by crossing your eyes,
by focussing you eyes at infinity (called the 'parallel' method
because the two lines of sight are parallel), and with an
inexpensive (or homemade) 3D viewer.
The viewer is nice because
it takes a little practise to see the images with the first two
methods, and most people find the viewer easier and more comfortable.
Taking the pictures
This is actually the simplest part. You can use any camera you
have available. Just take a picture, then move the camera to the side
a little bit, then take another picture. That's all there is to it.
I like to use a tripod, but some people just shift their balance from
one foot to the other for each shot.
The next step is to place the two pictures next to one another
and cross your eyes to see the 3D view. For cross-eyed viewing,
the picture that was taken from the right side goes on the left,
and the picture taken from the left side goes on the right.
If you have an instant camera, the pictures (of course) can be viewed
right away. I like to use a digital camera, because the pictures are
higher quality, and I can still see them right away on the screen.
Even if you use a standard film camera, the pictures can be digitized
on a scanner (either at home or through the services of your film
processing company) and then pasted together to be viewed on the
screen or printed on a color printer.
To view cross-eyed, keep the pictures at a distance where you can
comfortably focus on them. Slowly cross your eyes until instead
of two pictures, you see three. The center picture will be in 3D.
It takes some practice. If you find yourself straining your eye muscles,
you may be trying to focus on the air between you and the pictures,
where your eyes are aiming. Relax, and try again, letting your eyes
focus on the pictures, but cross so the left eye sees the right picture,
and the right eye sees the left.
Once you get the hang of it, you can do it comfortably right away, and
can view the pictures as long as you like, shifting your gaze from
items in the foreground to items in the background effortlessly. The
3D effect is stunning, not only because of the stereo effect, but because
there is twice as much information getting to your brain. It is almost like
In the pictures below, start with the smallest ones, and only go on
to the larger versions when you can comfortably get the 3D effect.
Sometimes it helps to start farther away, and move closer only when
your eyes are properly positioned and you can see the 3D effect.
Some people find it easier to aim their eyes at infinity rather than
to cross them. Because two light rays coming from infinity are parallel
when they reach your eyes, this method is called the 'parallel' method.
The problem with the parallel method is that the pictures must be the
width of the distance between your eyes. That's not very big, and that
limits the detail you can get on a computer monitor. It is less of a
problem with photographic prints (since they contain a lot more detail
per square inch than a computer monitor).
For parallel viewing, the pictures are reversed from cross-eyed viewing.
The picture taken from the right is on the right, and is viewed by the
In the photos below, find the size that makes the pictures on your
monitor close in width to the distance between your eyes. Then relax,
and let your eyes drift through the pictures as if they were viewing
a mountaintop far in the distance. You will gradually be able to see
three pictures as with the cross-eyed method, and like then, the center
picture will be in 3D.
For me, it sometimes helps to get very close to the screen, so the
pictures are very blurry. This makes it so that each eye is very
definitely looking at a different picture. Then, when I have a blurry
3D image, I slowly back away from the screen until it comes in focus,
being careful not to lose the 3D sensation. When you are very close
to the screen, it will look like the two pictures have merged into
one. As you back away, you will be able to see the other two pictures
flanking the 3D center image.
View these pictures with eyes parallel (looking at infinity)
All of these photos so far have been done with the 'hyper-stereo'
technique, where the camera positions are separated by more than
the distance between the eyes. For true stereo, try holding your
head completely still (rest it against a wall for example), and
hold the camera up to one eye for the first shot, then up to the
other eye for the second shot. These 3D images will work well for
objects that are nearby, and will not give the exagerated 3D for
distant objects that you see in the images of the lake in the
For very close-up objects, you can move the camera by less than
the distance between your eyes. Now, instead of seing the 3D
effect behind the plane of the picture, the image seems to float
in mid-air between you and the screen or paper. For this to
work well, you may need a special close-up lens on your camera.
However, sometimes just shooting the picture with a magnifying
glass taped over the camera sun shade will give very good results.
If you do want to play with the hyper-stereo effect, remember that
the brain finds it easiest to see 3D images if the distance from the
camera to the object is 30 times the distance between to two camera
positions. If an object is 30 feet away, the camera position for the
second shot should not be more than 1 foot from the position of the
The pictures below are done in true stereo, holding the camera first
to one eye, then to the other. The subject is the treehouse bridge
between two trees in my yard. It is 70 feet long and 45 feet above
the ground. You can see a little bit of my house in the background
in one of the pictures.
Remember, for the parallel viewing, each half of the picture must
be about as wide as the distance between your eyes. A little smaller
is usually OK, but bigger won't work. I am including some big images
just in case you have a remarkable computer monitor, or you wish to
print the pictures out and view them with a viewer.
Using a viewer to see the pictures
There is an inexpensive viewer available from a company called
that makes viewing these images very easy and comfortable.
They will send you the viewer by first class mail, so it may
arrive as soon as the next day.
The viewer is a simple pair of plastic prisms (with a bit of
magnification also) in a folding cardboard holder that keeps
the pictures at the proper distance. The prisms make it
easier for your eyes to view parallel format stereograms.
You can use the viewer to view pictures directly from the
computer screen, or you can place your own pictures next to
one another in the viewer. I print out mine on a good color
printer on premium paper. The trick is simply to tell the
printer to print the stereogram so it is 6 inches wide. This
is because the 3-D ViewMax viewer is designed for 6 inch
If you are having your own photographs printed for you, have
them printed 3 inches wide, so the stereogram will be 6 inches
wide when they are side by side.
It is a little difficult to build this kind of viewer yourself.
The magnification is not strictly necessary, so the viewer can
be made by putting a small wedge prism in front of each eye.
These prisms can be made by sanding and polishing small pieces
of clear plastic, but this takes some skill. Another way to
make a viewer is with small circular mirrors. The mirrors are
oriented 90 degrees from each other, and separated by the same
distance as your eyes. When you look into the mirrors, the left
eye will be looking left, and the right eye will be looking right.
The pictures are not stuck together in this viewer, but are
placed near the operator's shoulders, the left view on the left,
and the right view on the right. Such a viewer is more cumbersome
to use than the 3-D ViewMax, but it is easier to explain to
a younger child how it works, and being home-made, it might
make a better science fair project.
Click here for information
about the camera I use.
For more information on light and optics, see the
Next: Making permanent rainbows
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