Zapper, what's that?
The zapper is a simple device intended to fight against parasites that, if present in the human body, can do a lot of harm. As far as I know, it's not proved by any scientific source that it actually works, and despite time, it still stays in the zone of unproven/unscientific inventions. Personally, I think that it can work as described.
From a technical point of view, a zapper consists of a square wave generator, a resistor connected to its output that limits the power of the signal delivered to the body and two electrodes. One of the electrodes is connected to the mass of the circuit, second one is connected to mentioned resistor. Frequency can be adjusted from tens of Hz to tens of kHz.
Is it safe?
I don't claim that it is, but personally I think that it is if someone doesn't have cardiac problems. If you want to build it by yourself, you do this on your own risk.
Circuit of a zapper
Almost all Zippers are build from NE555, unfortunately I hadn't has it, so instead I used 4093 (2-input Schmitt NAND gates). The electrodes were made from aluminium foil.
The value of R1 should be 33k.