The easiest way is to use a TENS unit with adjustable frequency and pulse width.  TENS 7000 is inexpensive and easy to use.  You will also need 2 ear clips or 1 ear clip and 1 pad.  The pad can be placed on the shoulder or back of the neck.  The clip should be placed on the tragus of the ear.  If the ear clip is not staying, it can be placed on the cocha or the concha cymba.  The other clip can be placed anywhere comfortable on the ear.