Using only four components, the circuit shown in the next Figure can also be used to demonstrate the nerves stimulation or to make some experiments with electric shocks.
A pulsed current is produced by scraping the wire on a file, with the current flowing across the low voltage of the transformer. Thus, a high voltage is induced in the secondary.
Of course, this is the only way to produce a big voltage. If you keep the Wire in contact with the file after scraping, no high voltage will be induced because no changes will occur in the current flowing across the circuit.
A potentiometer and a neon lamp, as in the basic voltage, can be added to monitor and control the output voltage.
T1: Transformer, 117 or 220 V x 6 V - 100 to 500 mA
B1: 1 to 4 C or D cells
X1: Flat file
Other: Wires, cell holder (Optional), solder, etc.