As the winter months come up, many will be forced to stay indoors… To many, this will mean playing scrabble with grandma, watching television, doing puzzles, and sitting around the house. Why not begin an awesome project to spice up those potentially cold, dreary nights with an amazing light show decoration?
In this instructable, I will detail how you can do just that in creating an Audio Modulated Solid State Tesla Coil. Quite a mouthful isn’t it? For those foreign to the electronics engineering field or who simply just have no clue what “audio modulation” or “tesla coils” are, essentially what this device will do is produce visible streamers of electricity into the air (“lightning bolts”) pulsed at frequencies that correspond to audible tones (the device will “turn on and off” so quickly that the vibrations that the streamers make with the air sound like different notes). As we will see, we can exploit this neat effect to have the device play music and control it from behind a computer. So far, the secrets behind how these devices that sometimes make appearances on tv shows and movies has been kept under wraps and exclusively within the electronics engineering and computer science community or for very dedicated hobbyists putting in hours of research. In fact, for many high classes in elite colleges, n00b engineers would even have trouble making this on their own! This project could also be used to FREAK THE LIVING DAYLIGHTS out of people on Halloween! This year, I finished the project just in time to have this prop set up to play an eerie tune and trick-or-treaters were mesmerized (goes great to decorate a Frankenstein set).
This project is not for the light-hearted and is very difficult, but when completed, is extremely rewarding (it took me 2 years to learn how to build and finally do it). Not only will one learn loads about electronics and computer science, but simply taking this device to an event or (safely) to a public space rarely fails to produce a crowd of people taking pictures, impressed with your wizardly h@x0rz skills. Certain types of light bulbs or sticks will magically turn on without any wires. Good skills with power tools, machining, carpentry and the like are essential for crowd appeal. You have been warned, however, that there will be much tweaking, experimenting, and required dedication. In addition, be smart when operating tesla coils around sensitive electronics or in areas occupied by many people (basic common sense, I don't think there's much of a need to babble on, but if you are unsure, please work with an experienced engineer).
Step 1: What is a tesla coil?
Before going on, it is important to understand the basic functions of the primary components that make up our tesla coil and are used to make it (yeah, I know it’s redundant for most of you and most of you know how these parts work, but this instructable is for people from almost all backgrounds of experience):
Capacitor: Stores electrical energy and then releases it in short pulses (a little bit like a battery).
Transformer: Converts a lower voltage to a higher voltage (but makes output amperage go down) or converts higher voltage to lower voltage (making output amperage go up). Usually consists of coils of wire wound around a chunk of iron. The ratio of turns (how many times wire is wound around compared to other coils on the same chunk) of the coils determines how much voltage is increased our decreased. For there to be an output, a transformer must be fed AC (alternating current). In a tesla coil, the wires are not wound around a chunk of iron (and thus a tesla coil is sometimes called an “air core” transformer). In the tesla coil we will be building, a transformer such as a neon sign transformer is not required!
Transistor: Used for switching signals/voltage on and off. “IGBT” transistors are most commonly used, but require heat sinks.
Operational Amplifier: Used for increasing the amplitude (the “strength”) of a signal.
Tesla Coil Toroid: A metallic (usually made of aluminum) doughnut-shaped object with a small amount of capacitance (acts as a capacitor).
Microcontroller: Like a mini computer that can be programmed to perform a task.
Oscilloscope: Used to view what an electrical signal looks like (voltage over time graph).
Resistor: If put in a circuit it resists passage of electricity much like friction resists the passage of a moving object.
Potentiometer: Acts like a resistor but how resistive it is can be controlled with a little knob.
Inductor: Coil of wire that produces an electromagnetic field when electricity passes through it.
Rectifier: Takes Alternating Current and converts it to Direct Current.
Vector Board/Bread Board: Boards used for prototyping circuits. A breadboard does not require soldering to make connections, parts are just “plugged in.”
Ground: Usually denoted by a green wire, something connected to ground completes a circuit. Think of a lightning bolt moving from a cloud to the ground. In a similar way, electricity in a wire is attracted to and moves towards a ground connection.
Amps: A quantity that helps describe how much energy/power passes through something. Circuits in themselves typically have a limit to the amount of current that can pass through them and no more. A good way to think about it (though by no means is this a “scientific” definition) amperage tells you how concentrated the electricity is. In a welder, for example, amperage is very high because high concentrated energy produces a lot of heat.
Volts: This is also a quantity that helps describe how much energy that passes through something, but what it means for you and me is that it is a way to quantify how readily electricity “jumps” from one spot to another. HIGH VOLTAGE is characterized by the long electronic arcs coming from the tesla coil (typically over 100,000 volts). Electricity coming from the outlets in your house does not behave like this because the voltage is a lot lower (typically around 120 volts). A tesla coil steps the voltage way up, but that doesn’t mean that it just produces energy from nowhere. When voltage goes up, amperage goes down. When amperage goes up, voltage goes down.
Watts: A way to quantify total energy (combined voltage and amperage).
Check here for basic schematic symbols (we will need this later): http://library.thinkquest.org/10784/circuit_symbols.html
The operating principle behind a tesla coil is somewhat simple. Energy is sent to charge up a capacitor or set of capacitors. At a certain point, the capacitors are forced to discharge into the primary coil. When the energy that is stored in the capacitors is sent through the primary coil, a large amount of energy is induced (“sent”) into the secondary coil (alternating current is basically just electricity that changes voltage. When the capacitor fires, voltage changes from essentially zero to something really large in a very short amount of time). Since there are more turns in the secondary coil, the induced energy has a higher voltage, but a lower current than in the primary coil. The capacitors recharge and start this cycle again.
The capacitance of the capacitor and the inductance of the primary coil determine how quickly this cycle occurs per second and is measured in units of frequency called hertz. If a tuning fork vibrates at a certain frequency and another tuning fork that, if you hit it, would vibrate at the same frequency were put near each other, then simply striking one tuning fork would make the other start vibrating too. Why? Because of resonance. Tesla coils can be said to behave similarly; if the frequency of the primary circuit matches the resonant frequency of the secondary circuit, then the tesla coil is optimal, and like a tuning fork, energy will go from one part (the first “fork”/primary circuit) to the other (the second “fork”/secondary circuit).
In the olden days, capacitors would be charged up and a gap of metal would be put to each of the capacitor’s leads. When the capacitor was fully charged, a spark would arc inbetween the gap, thus forcing the energy into the primary coil. After the spark occured, the air inbetween the gap would be ionized. Ionized air acts sort of like a wire; electricity can move freely through it. Until the ionized air dissipated, energy would oscillate (move back and forth) between the capacitor and inductor many times. Instead of using spark gaps, we will be using transistors which are like little switches, but are controlled electronically. Turning the switch on and off quickly at certain frequencies will make the “lightning” coming out of the tesla coil make audible tones.
Keep in mind that even though we are turning the tesla coil on and off at a certain frequency (a certain number of times per second), its primary circuit is still oscillating (energy moving back and forth between the capacitor and primary coil a certain number of times per second) at a different frequency that we will match with the secondary circuit.
I have attached a simplified diagram of the basic way that we will hookup the tesla coil. This instructable is designed to be very flexible and allows for you to be your own designer through giving you the tools and basic knowledge needed to build one yourself from scratch.