I tried to build some TENS device, but lost in "safety maze".

I reverse engineered some existing device, there are TONS of safety measures.

At least: current limiting resistor, transformer, voltage/current feedback, GND isolation, MCU protection.

After replicate all of these, I still not brave enough to try it myself, I just find it too dangerous.

PS: TENS device is fun. article seems like a bait.

The two BJTs do limit current to 20mA on all finger outputs. Voltage feedback is also set up to ensure maximum 32V. MCU protection, well just a ferrite bead.