Just a small post to clear things related to all these urban legends and project comments.
An EMP generator would not 'increase' money when used near a slot/vending machine, it would just cause the machine to fuck up and die not to start adding money.
Vending machines / slots machines dont fail open otherwise you would just be able to unplug them and snacks would fall out.
Magnetic locks and physical dispensers are used to put out money, an EMP would cause failure of the electronics roughly the same as a power outage.
Additionally, solutions like this are used on modern machines: http://web.archive.org/web/20140225014135/http://www.defendertris.com/ENG/index-en.html
The effects of an EMP on consumer electronics can be found here: http://www.dtic.mil/dtic/tr/fulltext/u2/a210505.pdf
Related to the "Multifrequency EMP Generator" sold on marketplaces such as eBay or AliExpress they are all bullshit, their antenna is optimized for a single frequency, attempting to get multiple frequencies with that is like trying to talk to a space station with your garage door opener.
If you looks for hacking this kind of materials, just get a bus pirate from sparkfun and start to analysis trames, simple as that.