How to Make a Square Wave to Sine Wave Converter
Sine waves rise smoothly to a maximum, then fall in a mirror image pattern to the center line. This "hill" is then repeated upside down in a mirror image "valley." This pattern of smooth mirror image hills and valleys repeats endlessly. This wave describes AC electricity, light waves and radio waves. A square wave has all right angles. It goes directly to maximum then falls down to the mid-line before repeating the square "hill" in an equally square "valley" indefinitely. Square waves are often produced with batteries and rotating mechanical devices -- as in automobile alternators.
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Instructions
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Put a coil in the circuit to resist sharp changes in the voltage level. electricity flowing into a coil creates a magnetic fields which opposes the flow of electrons. This effect is produced as long as the voltage level is changing. This means that both rising and falling currents -- but not steady levels -- are opposed. The coil knocks off the corners of the square wave.
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Add a capacitor to the circuit to make the coil's opposition to changing currents smoother. Capacitors are just two plates separated by a thin sheet of insulator. They can act as a temporary high speed battery. If you put a charge on a capacitor, it will be retained briefly before dissipating. When the coil starts opposing the buildup in current, the electrons in the surge pile up on one plate of the capacitor. These electrons are then released when the current through the coil stops changing.
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Scale the sine wave produced by the coil and capacitor with a resistor. A resistor is a device that opposes the flow of current. It does not change the shape of a wave, except to make it uniformly smaller. The coil and capacitor combination has the effect of changing the square wave by knocking off the corners and increasing the peaks. The resistor scales this result down to the size you want.
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Tips & Warnings
An easy way to get the values of the components correct is to use a variable resistor. Use whatever coils and capacitors you have handy with the variable resistor. Turn the variable resistor until you have the sine wave you want, then install a resistor with the same value as the variable resistor.
Sometimes a single coil and capacitor will not produce a sine wave as smooth as you want. You can get a smoother wave by doubling the components -- two coils in series with a capacitor across the circuit in front of each coil. You will still need only one resistor.
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