Transcutaneous electrical nerve stimulation (TENS) is a technique that applies electrical current to nerves and muscles for the relief of pain. Before you ask, yes, some of these devices are FDA approved for various ailments. [Eric], [Conor], [Jacob], [lnr0626] and [rdrdrdrd] were down at HackDFW this weekend and built a TENS device from parts in their scrap bin.
A semi-decent TENS machine can cost somewhere between $70 and $200, but the team here have reduced the cost tremendously simply by separating the futzing analog/contact pad part from the signal generation part of the project. The signal generation actually happens on an Android phone, with settings to ‘relieve pain’, ‘relax’, ‘pulse’, and ‘random’. These signals are generated as audio and sent out over the headphone port. From there, the signal is amplified and sent to the neat skin-contact pads.
After prototyping their circuit, the team actually etched a circuit board for the final phase of the hackathon. Demo video below.