Simple Laser Communicator

How would you like to talk over a laser beam? In about 15 minutes you can set up your own laser communication system using a cheap laser pointer and a few parts from RadioShack. The audio signal from a microphone varies the power feeding the laser, so that its brightness changes, following the shape of the original sound wave. At the receiving end, a solar cell or photo-resistor converts the oscillating light signal back into the original sound.

The communication is completely private, with no wire connection to tap into. Only you will be able hear what comes over the secret laser link.

Check out more Weekend Projects.

December 18, 2012, 10:43 pm PST

Parts
/
Tools

Parts

Laser pointer You can get one for $10 from my Scitoys Catalog, scitoyscatalog.com or from RadioShack, part #2103037.
Batteries, 1.5V, any size Get the same number of batteries and voltage that the laser takes, typically 3x 1.5V.
Battery holder for the 1.5V batteries If you can’t find a 3-battery holder, wire a 1-cell and a 2-cell holder in series, or use a 4-cell holder and bridge 1 compartment with wire.
Stiff wire or rubber band
Audio output transformer, 1kΩ primary coil, 8Ω secondary RadioShack part #273-1380 or Scitoys Catalog #XFORMR
Alligator clip leads (2–10) with points fine enough to connect to the inside of the laser pointer. You can substitute wire and solder, but the clip leads are easier. RadioShack #278-1156 will do nicely.
LED, 2-lead bicolor to protect the laser from voltage spikes if it doesn’t have built-in protection.
Hookup wire
Mini portable amplifier such as RadioShack #277-1008. Alternately, you can use a stereo system.
Microphone with cable and plug that fits amplifier or stereo input
RECEIVER OPTION #1: SOLAR CELL WITH EARPHONE (SIMPLEST):
—Small solar cell Scitoys #3SOLARCELLS
—Piezoelectric earphone Scitoys #EARPHONE
—Transparent tape
RECEIVER OPTION #2: PHOTOCELL WITH EARPHONE (CHEAPER AND STURDIER):
—Piezoelectric earphone Scitoys #EARPHONE
—9V battery and battery clip
—Photoresistor, cadmium sulfide (CdS) RadioShack #276-1657
—220Ω resistor

Tools

Soldering Iron, 15-Watt from RadioShack #2062728
Solder, lead-free from RadioShack #2062722
Radio, transistor from RadioShack #3705831
Audio plug, 1/8", mono from RadioShack #2103854. One to fit your radio, and one to plug into the mini amp. (Instead of the mini amp, you can also plug into a stereo or larger amp, using an RCA or 1/4" audio plug, also available at RadioShack.)
Helping Hands tool (optional) from RadioShack #3928375

15 Responses to Simple Laser Communicator

Simon Quellen Field on November 21st, 2012 at 4:28 am said:

All of the component specifications listed appear correct to me.
What problems were you having?

This project is based on this one:
“http://sci-toys.com/scitoys/scitoys/light/light.html#laser_communicator”
and the kit can be found here:
“https://www.scitoyscatalog.com/product/LASERVOICEKIT.html”
Simon Quellen Field on November 23rd, 2012 at 5:20 pm said:

The second link has the transformer you need.
Scitoys.com ships all over the world.
Simon Quellen Field on November 26th, 2012 at 2:53 am said:

The whole kit is available here:
http://www.scitoyscatalog.com/product/LASERVOICEKIT.html

The transformer by itself is available here:
http://www.scitoyscatalog.com/product/XFORMR.html
Simon Quellen Field on December 2nd, 2012 at 7:46 pm said:

Check the voltage required by your green laser, and the voltage actually delivered.
Simon Quellen Field on January 20th, 2013 at 2:28 am said:

You’d still want the transformer to mix the signals.
But a pair of resistors would probably work also.
- Darren on May 5th, 2013 at 9:35 pm said:
  
  Can I use the audio output transformer with these specs?
  AC resistance @10khz : 2KΩ-0-2KΩ (primary), 95Ω (secondary)
  
  Inductance @10khz : 19.2mH-0-19.2mH (primary), 0.88mH (Secondary)
  
  Turns ratio approx : 22:22:1
  
  DC resistor approx : 39Ω-0-39Ω (primary), 1.5Ω (secondary)
Van Haute on January 20th, 2013 at 9:13 pm said:

If I understand you, you suggest to lower the full output of the radio by using resistors ? Right you are old chap ! What is your location ? I am calling you from Antwerp Belgium. So long !
Margot Paez on March 14th, 2013 at 7:08 pm said:

Can I use some cheap earphones in place of the crystal earpiece? I have a pair that I don’t need and that’s easier than finding a place that carries the crystal kind…
Mike Keith on October 26th, 2013 at 1:28 pm said:

I’m Confused. I can’t get the simple input circuit to work. When I add the transformer in series with the batteries the laser pen no longer works. Works A-OK if I short the transformer while it’s in the circuit. All versions of this experiment reference a 4.5v battery source but my pen is 3.0v. Does the laser type (4.5v vs 3.0v) or battery voltage make a difference? If so, you’d think this would have been mentioned along the way…
Thanks for help, Mike
Pingback: Laser Communicator WITHOUT Audio Output Transformer | mklec blog
Guest on November 25th, 2014 at 5:41 am said:

Hi, is the current in this setup AC or DC?
- rob beesley on September 10th, 2015 at 1:52 pm said:
  
  you can see the batteries so it is dc
El Shanty on October 13th, 2016 at 3:46 pm said:

I have problem, I did the laser communiucator but it noesn’t work, which is the problem?