HOW TO: Send Audio/Your Voice Over a Beam of Light

Step 4 The Receiver

The receiver is so simple, a monkey could do it. All you have to do is solder the CdS photocell in series with the battery pack (3 volts), and then solder the two resulting leads to another mono jack. Use the biggest photocell you can find. Also note that it does not matter which way you connect the photocell; it has not plus (anode) or minus (cathode) sides.

Comments

[DoItOrDie]

Here's something for a transmitter you might like to experiment with. Glue a little mirror on a speaker and shine a light source onto it such that it reflects to the photocell receiver. Make sure just the edge of the light hits the photocell (about half way) so that, as sound comes from the speaker, the light covers the photocell a varying amount. The idea is the reflected light from the speaker will cause the edge of the light beam to just cover about half the photocell with no sound and vary in the area of cell covered as sound causes the beam to move. For this, a larger area photocell might be good. Perhaps a photovoltaic cell as opposed to a photoresistive cell. Any source of light could do, even sunlight. A laser would be good as it remains in a nice tight bundle over a long distance, making it easier to "calibrate." One consequence of this setup is that it will become more sensitive the greater distance between the transmitter and receiver. That is, it will take less movement of the speaker to cause a given change on the photocell the farther away it is from the transmitter. Also, the intensity of the light source is independent of the power required to modulate it. FYI, this sort of thing makes a good vibration sensor, such as for a seismic acivity detector. The greater separation, the more sensitive it is.

[mortaldoom780]

I have a question about using a laser. I have tried using one, BUT it doesn't work. I am using a (almost) 5mw green laser pointer, and it will not light when I hook it up. I have the right polarity, and the right voltage (2 AAA's). The output ranges anywhere from 2V to ~3.080V. That's another problem. I need to have MORE batteries than the laser needs, so that it is always getting the minimal amount of power it needs to work, right? Therefore, I am going to need something to protect the laser from being overloaded. Say I am using a standard, 3 button-cell, cheapo laser pointer. As you know, the universal voltage for all of those cheap lasers is 4.5V. Exactly what rating resistor do I need? Or do I need to use an LED rated at a certain voltage? If so, how much? By the way, thanks for the info!

[SnuffyDaPenguin]

Looks like what you need to do is check all your wire connections, because if it were connected well enough, it wouldn't vary in power. I had this very same problem when I built my Tesla coil for my school science fair. Just make sure you get as good of a connection as possible.

[WilderLust]

one thing to remember is that LEDs are current sensitive so you need to have a current regulator. this is easy to do but i can hardly tell you how in a message like this... you can look at the many LED instructables to get info on some of the methods. i have LED controlers i use for my projects. if you are interested in electonics, there are great tutorials on the web you can learn from. one example is http://www.allaboutcircuits.com/ for the specific laser you have, see if you can find the part number (if it is stamped on it) and look for the datasheet for it here: http://www.datasheetcatalog.com/ this is the best source for detailed data on parts you salvage. i have been meaning to make an instructable on salvaging electronics and resources for people to start learning and playing with stuff for free but i dont seem to get around to it!
anyway... if you really want to play with electronics, i would recomend you start building tools to do it like a variable powersupply. there are so many projects on the web that you can make stuff pretty cheap especially if you get your parts for free :-)
i warn you though... it is adictive! i am spending all my time playing with electronics!!

cheers,
wl

[mortaldoom780]

Thank You!

[WilderLust]

You are most welcome :-)