You probably know that radio waves can transmit audio, but did you know that visible light can do the same thing? Using a very simple circuit design and some commonly available parts, we can easily construct a device which allows us to transmit music wirelessly through LED lights!
Step 1: First Things First: the Circuit
The picture above is the outline for the circuit which we will shortly build. Notice that it is very simple; only a half a dozen or so components are really needed to construct this device.
Step 2: Parts List
The necessary parts can be purchased for anywhere in the neighborhood of $15 to $50. They are as follows:
1. High-Brightness White LEDs. You'll want to have at least 2 of them. The higher power they are, the better!(Provided they're rated for 3 - 3.5 volts)
2. A diode. You don't need any specific type; I stripped this one out of a shot bridge rectifier.
3. (Optional) a 10 ohm resistor. If your LEDs are high-current types and you have several of them, you'll probably be fine without a resistor. But if you only have a couple and/or they're traditional low-amperage LEDs, ensure that you've got a resistor that is between 10 and 100 ohms. Higher resistances are needed for lower current bulbs.
4. Breadboard / PCB board. This is just to have a frame on which to build the circuit.
5. MP3 Player and audio cable
6. Headphones or speaker with standard audio connector
7. A solar panel. Generally, you will get better results with higher-voltage panels. The one shown in this picture is rated for 6 volts, though I have a larger one rated for 12 (and it works somewhat better).
8. 6V lantern battery. Trying to use lower or higher voltages will not work. I'll explain why later.
8. Spare copper wiring. Lots of components, gotta connect 'em!
Step 3: Building the Light Panel
The most important part of this project is the light panel. It is the heart (and the MP3 player is the soul) upon which the rest of the "transmitter" is built.
Since we are working with a 6-volt power source and using 3.3-volt LEDs, we'll need to start by wiring the LEDs in series of 2. Once you've wired up a few pairs of LEDs, effectively transforming them into 6.6-volt bulbs, you can then stack as many of these pairs in parallel as you wish. Generally, however, I'd say that 5 or 6 pairs in parallel (10-12 individual lights) is plenty. We are not attempting to drive these at full brightness; the nature of the circuit will not allow them to get much brighter than perhaps five or ten percent of their rated capacity.
Once you've completed your light array, connect it to the battery to test it out (preferably with a small resistor, particularly if you've got lower-powered LEDs).
Step 4: The MP3 Player Interface
Setting the light bar aside, the next order of business is to figure out a way of connecting our MP3 player to the assembly. This can be done using a pre-made 3.5mm headphone jack, or (for cheaper and quicker) a few pieces of copper wire.
Right away, as you examine the end of your audio cable, you'll notice that it is divided into three parts. Our goal is to connect two of these three parts to the circuit. To accomplish this, take a small piece of bare copper wire - perhaps 4 or 5 inches in length - and wrap it tightly around the outer tip. You can twist the wire together after you've wrapped it three or four times around the plug, further securing the grip. Ensure that you leave at least two or three inches of copper to spare so that you can connect this to the circuit later.
Next, find another piece of bare copper wire, and twist it tightly around the innermost segment (the portion of the jack opposite the outer tip). If all goes well, once you've secured both connections, you should have copper wire looped around the 1st and 3rd segments of the jack, with the middle segment being left completely untouched by the wire. At this point, if you so desire, you can wrap insulating electrical tape around it to secure the wires firmly in place.
When you're done with this step, your assembly should look something like the photo above.
Step 5: Wiring the Circuit Together
Believe it or not, we're now almost done with the main circuit!
All that's left to do is connect the resistor (if you have one) and the diode to the assembly. Being that the diode is the more important part of the two, let's begin with it.
As you observe the diode, you will notice that it has a band on one end of it. This band shows the direction in which current will pass through. To make a complete circuit, make sure that your diode's band is "pointed" towards the negative side of the circuit. This is hard to explain, and it is better visualized by looking at the circuit diagram back at the beginning of this Instructable.
One side of the audio jack will be connected to a resistor (or lack of a resistor), which will in turn be connected to the positive terminal of the battery. The opposite connection of the jack will be joined to the diode (the non-banded side).
Connected to the banded end of the diode will be the positive terminal of your LED panel. The negative end of the LED panel is then attached to the negative battery terminal, and voila! The circuit is now complete. All that's left to do is to plug the free end of the audio cable into an MP3 player and pull up your favorite song. But before you do so...
Step 6: The "Reciever"
In order to be able to listen to your favorite song, you'll need a pair of headphones and a solar panel. What we need to accomplish for this step is essentially the same thing as what we did to connect the MP3 player to the transmitting circuit.
Start by attaching a copper wire to the tip end of your headphone connector, making sure to leave two or three free inches of wire. Attach another wire to the third segment of your connector, opposite the first connection you made. To solidify your connections, wrap some electrical tape around the jack, ensuring that the wires do not become crossed. This will only allow you to hear sound in one ear, but the quality of that sound should be near what you'd expect if you plugged your headphones directly into the MP3 player.
So, congratulations! You've just made a visible-light-to-audio-converter. One interesting thing to try at this point in time is to hold your solar panel up next to a light fixture in your house. If you have LED bulbs, you'll hear a faint buzzing through your headphones, as the lights are actually flickering on and off 60 times a second due to the frequency of the mains power supply! If you haven't gotten around to buying any LED lights yet, turn on a TV and hold your panel near the screen. Be prepared to hear a lot of crackling, buzzing, and popping as the solar panel picks up on the light streaming from the monitor.
Step 7: Listening in
Now that we've completed both parts to this project, all that's left to do is to fire it up and listen. Connect the circuit to the battery, plug in and turn on your MP3 player, and hold the solar panel within a few inches of the LEDs. If all goes well, you'll be hearing your favorite song playing over the 'light waves!' Additionally, make sure to watch the lights during more fast-paced or aggressive parts of the music, as they may flash and dim slightly with varying audio intensity.
Step 8: How It Works
Essentially, this circuit enables us to 'encode' audio information onto light waves.
For a typical setup, the LEDs would be powered solely off of the battery. Since the current provided by the battery is DC (direct current), there would be absolutely no variance in the light of the LEDs. But if we stick the audio jack in between the lights and the battery, everything changes.
When the audio cable is connected to the MP3 player, the MP3 passes a tiny electrical current through it. Normally, this current would be used to power your headphones, since headphones are little more than super-advanced electromagnets which take very little electricity to run. But in this project, we are forcing that tiny signal to instead 'interrupt' the flow of electricity to the LEDs.
Now, the cool thing to note (and the little bit of science which makes this project possible) is that the interruption in the electricity causes those LEDs to 'flash.' Moreover, that flashing occurs in exactly the same pattern as the interruption. And since the so-called interruption is, in fact, a signal carrying music, that means that the lights are now 'transmitting' the information which is the MP3 player is spitting out.
In a fashion similar to how a radio antenna receives broadcasts, we then use a solar panel to convert the pulsating light frequency back into electricity, which the headphones can convert to sound energy. Ka-boom! You're now listening to music.
Step 9: Some Random Notes
About the "Balance of Power"
Earlier in this Instructable, I mentioned that we would need the power supply to be exactly 6 volts. But why is this? Essentially, it's because we need to 'balance' the power in the circuit with the signal from the MP3 player. By putting too much power through the LEDs, one would end up over-driving the circuit, thus drowning out the signal and garbling the audio.
I actually tried a variation on this project several weeks ago in which I powered an LED panel with a 12 volt power supply. But since the voltage was well in excess of what the LEDs were technically rated for, it left all that extra current to travel straight into the connector jack, scrambling the signal and making the music impossible to listen to. It is very possible to scale up this design, but you always want to ensure that your LED panel's rated voltage is slightly higher than your power supply's output. In our case, we are powering 3.3 volt LEDs (6.6 volts when two are placed in series) from a battery which can push out - at most - 6.5 volts. Thus, all the excess voltage is dropped off by the LEDs, leaving the signal pure and clean.
The Picture Above
I took the photograph shown above in my room. Several years ago, I was the lucky recipient of a 100 watt solar panel as a gift. Now, the first solar panel I used for this project was a small 6-volt setup which could fit on the back of a cell phone case. But being the curious soul that I am, I decided to scale things up a bit and plug an MP3 speaker into my 100 watt panel.
It actually ended up working out a lot better than I anticipated. By turning the lights off and simply setting the music circuit in the center of the room, I could clearly hear the music coming through the speaker, which was being driven by the solar panel sitting several feet from the LEDs! I can only imagine what heights this project could be scaled up to. And that makes me think... might the sun be used to transmit music? Well, the world may never know.
Thanks for reading, and check back often! Also, feel free to visit my blog - the link is directly under my username.