Introduction: Build a Wind Harp!
A wind harp is just what the name says, a harp played by the wind. You don't need lessons with this instrument, just a light wind will do. This design uses four steel strings and two magnetic pickups made with a pair of nails. You can build one with just one string with good results. Mine is 8 feet long, but you can make it as short as 2 feet or as long as you want. I mounted the wind harp on top of a shed and connected the signals from the pickup to my PC inside the house. I broadcast these sounds 24/7 on the internet radio using ShoutCAST. You can hear the wind harp at: http://home.comcast.net/~botronics/windharp.html
I also have some blogs about how to set up your own internet radio station at the above link.
I use Solar Garden lights to power this project, but for this instructable, I'm showing the basic concept of the construction. How you power it is up to you.
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Step 1: Make the Support
The wind harp support was constructed from a 2"x2" by 8 foot long pine lumber I just happen to have. Prime and Paint to protect from the elements. Remember, its a wind harp that needs to be outdoors. Although a smaller one can be made to fit a window sill.
I used 1/2 inch steel angles at the ends to support the wires with screw eye bolts. 24 gauge solid steel wire from the hardware store is used for the strings. You can try different thickness for different sounds. Just remember they must be steel or iron, the strings vibrations must interact with the magnetic field produced by the pickup coils, just like a electric guitar.
Step 2: The Magnetic Pick Up
As the wind blows across the strings, vibrations will begin at various harmonics of the strings fundamental frequency. Simply stated, if you puck the string, you will hear the fundamental frequency.
The wind causes multiples of that frequency to vibrate up and down the wire.
To hear the sounds, I use the same method an electric guitar uses to amplify guitar strings. A magnetic pickup is made by winding many turns of # 40 wire on a nail. A magnet is attached on one end to make it magnetic. When this coil is brought close to a vibrating steel wire, tiny voltages are generated and amplified with a preamp. These voltages are connected to my PC sound card. Two are used together to buck out local hum inducing magnetic waves. More on this later.
Each coil was made using a nail. The point on the end is cut off and the nail is chucked on a table top drill stand. Small plastic washers were super glued on the nail to hold the wire in place during winding. I didn't count how many turns were wound, but tried to make each coil about the same. The closer the two are a match, the better the hum bucking. Each coil is held over a string with an angle made of aluminum. Plastic ties hold the coils to the bracket. I wrapped each coil with a piece of rubber hose to deaden vibrations from the frame.
Step 3: Winding Pickup Coils
Wind the coils on the nails with a table top drill press or use a hand drill. I used #40 enamaled wire, but it could be a bit thinner or thicker. Use AWG size 36 to AWG 43. You can get the wire at Stewart-MacDonald. http://stewmac.com They also have kits for making electric guitar pickups.
I haven't actually tried using an electric guitar pickup, but I don't see why it wouldn't work. After all, what you are building is a guitar that is "blowing in the wind". With a guitar pickup, the strings would need to be spaced 1 cm from each other, just like in a real guitar.
The magnets I got from a local Arts and Craft store. Use the super strong neodymium type. You can use just one coil, but it will also pickup surrounding ambient ac "hum". To make it "humbucking",two coils are used. Because the coils are connected with opposing phases, any hum pick up is bucked out.
Notice the magnets on the other coil is reversed. This will cause the other coils pickup polarity from the wire to be reversed. Connecting the two coils in series makes the pick up from the wires to be additive. Just like placing batteries plus to minus in series.
Step 4: Amplifier
To amplify the tiny signal you will need an IC amplifier. A LM386 works will for this project. I made a special pc board, but it can be built on perf board. Keep the amplifier near the coils and bring out your signals using shielded wire to your PC. With my solar powered version, I used the solar garden lights as a housing for the circuit. You can connect the amplifier with a minumum of wiring with 2 conductor shielded wire. The shield can be the common and power negative, while one lead can be power positive and one lead the signal out.
Step 5: Connect to Your PC
After you build the frame, coils and amplifier, its time to test your wind harp. If everything is working, you should hear a loud "twang" when you pluck the steel wire.
For the best harmony, you can adjust the tension on the eye bolts so all the wires are the same frequency. The two inner wires are the strongest performers, while the two outer "passive" wires add some sound through mechanical connection at the single eye bolt end.
You will find that the harp responses to the slightest wind. Higher winds create higher frequencies. To protect the coils from rain, I placed a plastic cup as a cover above the coils.
When it rains, the wind harp becomes a rain harp, making very nice tones as the drops hit the wire.