Buzz
With a basic laser pen, some miscellaneous parts, and just about 15 minutes of your time, you can construct a rudimentary laser communication device. This setup effectively turns an audio signal into a beam of light, which crosses the room and reconverts to audio with negligible loss of quality.
Procedure
First, extract the batteries from the laser pointer.
Before proceeding, remove the laser pointer's batteries. This is crucial for gaining unobstructed access to the battery connection point.
Attach a clip lead to the battery's spring.
Typically, there's a small spring where the clip lead can be fastened. The other end of the battery usually connects to the laser's casing. Given the variety of laser pointer designs, you might need to experiment with clip lead placement to ensure compatibility with the new external battery pack. Additionally, you may need to secure the laser's push button switch with a rubber band or wire.
- Before connecting the transformer, test the connection to ensure the laser functions with the new battery pack. If it doesn't illuminate, try reversing the battery. Reversing the battery won't damage the laser.
Attach the transformer.
Link the 1,000 ohm side of the transformer between the battery and the laser. The 1,000 ohm side of the transformer features three wires, but we only utilize the outer two. The inner wire, known as the center tap, remains unused in this setup. Test the laser by connecting the battery. It should function properly at this stage.
Connect the earphone jack to the transformer.
Attach the earphone jack to the 8 ohm side of the transformer. Refer to the transmitter schematic.
Hook up the receiver.
Setting up the receiver is a breeze. Simply connect the solar cell to the microphone jack and plug it into the amplifier or stereo's phono input. The orientation of the wires on the solar cell doesn't matter. Consult the receiver schematic for details.
Insert the laser's earphone jack into the radio.
Ensure the transistor radio is off and the laser is on. Then, plug the laser's earphone jack into the radio's earphone socket.
Link up the solar cell to the amplifier.
Once the solar cell's connected to the amplifier or stereo, crank up the volume until you catch a hissing noise. Then, dial it back slightly until the hiss disappears. The volume setting should be relatively high, akin to what you'd use for blasting music.
Direct the laser beam across the room to hit the solar cell.
You might hear clicks or pops emanating from the stereo or amplifier as the beam crosses over the solar cell. This signals that everything's functioning smoothly at this stage.
Switch on the radio and adjust the volume.
Gradually adjust the volume until you can hear the radio station voices or music coming from the amplifier across the room. The radio should be just audible without the earphone jack, not excessively loud. If you can't hear the sound from the amplifier across the room, ensure the laser is shining on the solar cell, then attempt to increase the amplifier's volume before adjusting the radio's volume.
- By now, you should hear the radio station clearly through the amplifier across the room. Interrupt the laser beam with your hand and observe the music stopping.
Insights
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Ensure your laser pointer produces a dot rather than a shape, such as an arrow.
Cautions
- CAUTION: Directly looking into the beam of any laser pointer can harm your eyes.
- It's advisable to use laser safety glasses suitable for the type of laser you're using.
- Class III lasers pose a significant risk to the eyes, while Class IV Lasers can ignite flammable materials and cause severe eye and tissue damage, emitting more than 5mW (0.005 watts). While common laser pointers and this circuit are unlikely to power such high-powered lasers, handle all lasers with caution, like firearms, pointing them away from eyes, reflective surfaces, and flammable objects at all times.
- Infrared lasers are particularly hazardous as their output is nearly invisible but can still cause serious eye damage. Avoid looking directly into any laser beam, even if it seems weak. Infrared lasers are also unsuitable for this experiment as they are not considered 'cheap' and are difficult to align accurately.
Essential Supplies
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For the Transmitter:
- A budget-friendly laser pen pointer
- A battery holder matching the laser's voltage requirements (Often 3 cells)
- A transistor radio or any sound source
- An earphone jack suitable for your sound source
- An audio output transformer consisting of an 8 ohm coil and a 1000 ohm coil (Radio Shack 273-1380)
- Several clip leads (wires with alligator clips on the ends) to assemble everything. Ensure at least one lead has a long, slender point to connect to the inside of the laser
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For the Receiver:
- A small solar cell (Radio Shack 276-124) or photoresistor + battery (as illustrated below)
- A mono microphone jack compatible with the phono input of your stereo
