Long before police were tasering belligerent drunks, prepubescent Midwestern boys were tearing apart broken camera flash units and making simple cattle prods to surprise and delight their friends: the Ticklebox—a sinister name for a sinister toy. This particular design, and its packaging, was the brainchild of a boyhood friend’s teenaged cousin. Jiggle the foil-covered box and enjoy a brisk, but safe, 100-volt jolt. You could make up a game using the box (LARP Operation™? Hungry-Hungry Don’t Tase Me Bro!?) but what’s the point? High-voltage, low-current self-administered electrocution is its own joy.
The heart of the Ticklebox is a step-up transformer, a device that cunningly uses electromagnetism to step up a low voltage to a higher voltage. In this case we’ll be slightly abusing a RadioShack audio output transformer, which is actually a step-down transformer, wiring it backward so it works as a step-up transformer.
The rule to remember is this: Whenever you have an electrical current flowing through a wire, it creates a magnetic field, and whenever you have a magnetic field moving past a wire, it will induce an electrical current to flow through that wire.
A transformer is composed of a square iron donut with two opposing sides wrapped in coils of thin enameled wire (thus, each side can function as an electromagnet). Our step-up transformer has a few wraps of wire on its primary side (the side we’re applying current to), and many more windings on its secondary side (the side that we’re using to shock folks). When a current pulses through the primary coil, it creates a magnetic field in the iron donut, which in turn induces a current in the secondary coil. Since the secondary coil has more loops (and is thus a longer wire), a larger voltage is induced on the secondary side. Handily, the ratio of wrappings between the secondary and primary coils determines the factor by which that voltage is multiplied. Since our RadioShack transformer has 11 times as many coils on the secondary side (when we wire it our way, which is backward to what it was designed for), the voltage on the secondary side is 11 times higher. So, when we pulse 9 volts through the primary coil, the secondary will produce a brisk 99 volts, give or take. (Compare this to the static shock you get while pulling off a sweater, which can be several thousand volts.) But you can’t get something for nothing: When a transformer steps up voltage, it steps down current by the same factor. So, in this case, the final shock is 100 volts but a very safe handful of milliAmps. Contrast this to a fat wintertime doorknob static spark, which might be 7,000 volts, but just a few microAmps. On the other end of the spectrum, a paramedic’s defibrillator paddles can zap you with a few hundred volts at several dozen amps—which is several thousand times the current delivered by the Ticklebox. (For a more complete discussion of voltage, current, and personal safety, flip ahead to the appendix or back to Voltage, Current, and Resistance in Voltage, Current, and Resistance.)
