Step 5: 555 timer driver
Another popular coil driver is the popular is this 555 timer driver.
it oscillates a transistor that drives the coil. its a little more costly and complicated but its overall relatively simple.
you can tune the output by the POTs. I haven't made the driver yet
simple____ || ________________hard
$0.01_____ || ________________$50+
harmless shock ____ || _________________electrocution