Info



What is “MoLZ?” MoLZ is Music over LaserZ and it is exactly as it sounds…transmitting music (really, any kind of audio) using a laser.


I bought a laser pointer recently because I had some fiber optic cable at work and I wanted to shine a laser through it. The result is actually pretty underwhelming so don’t expect unicorns jumping out of the other end of the cable if you ever decide to try that. ANYWAYS, coincidentally, the following day I was browsing through Hackaday and I saw that Treehouse Projects had a project that transmitted music using a laser pointer. Naturally, this intrigued me and I decided to recreate it myself. However, I wanted to see if I could transmit music from one end of a street block to the other.

Here’s a brief run down of the experiment…



Here are a few pictures of the transit with the transmitting components on it:

TX Circuitry Attached to Transit



Laser Attached to Optics



Looking through the Lens with Laser Powered Up



So…why have the optics? Well, that surveying transit is a bit overkill but it looks so darn cool! The optics are needed because the laser dot gets bigger and bigger (and hence, fainter) as the transmission distances get greater, therefore power is also spread out over the increasing area. I want to concentrate all the power back into a relatively small area (hoping to get a stronger signal) and lenses can do just that.

By the way, if you don’t know already (and I’m sure you do) NEVER EVER look into a laser beam and especially, don’t you dare look into the lens if you shine a laser through it!

Circuitry



The circuit is very VERY sloppy, but as a quick weekend project, it works. At the top, we have the transmission circuit. We have a bias voltage source with a pot to knock down the 5 V to around 3.2 V (for powering the laser and giving a fairly good swing range). We then mix in the audio signal then pass off the result into the laser diode. I didn’t have an audio transformer handy and that did cause a fair amount of pain but it worked.

At the bottom, we have the receive circuit. From the 9 V battery, the voltage divider knocks the voltage down to about 5 V. The photoresistor receives the laser/music signal and rides on the 5 V bias. The decoupling capacitor then takes in the signal and puts it through a low pass filter (to filter out any fuzz). From the filter, it is sent off to the amplifier. Here is the result…



So yes, from about 100 m away, we can transmit music AND hear it! Success!
Anything else? YES! What we did here was Amplitude Modulation. We varied the brightness of the laser, which translated into varying voltage amplitudes. Also, I was playing with a gyroscope earlier and put it between the laser and the photoresistor. Because this was like turning the laser on and off really quickly, I made a square wave generator. Pretty neat!

Finally, Here’s a picture of the moon I took through the optics of the transit. Not too shabby!

Credits: Business Cat Image from [Know Your Meme].
Big thanks to Ben for helping me out with the experiment and staying out in the cold with me trying to get MoLZ to work as passers by probably thought we were weirdos.