I built a TENS unit with an Teensy and decided to skip a current sensor. Real switching power supplies regulate current too, not just voltage (a low Ohm shunt a

I built a TENS unit with an Teensy and decided to skip a current sensor. Real switching power supplies regulate current too, not just voltage (a low Ohm shunt across one of the stages to an opamp that tells the PWM circuit to slow down the n-fet input pulses, in addition to the voltage feedback power gate). The funny part is: I didn't shock myself, I punched myself. I had the electrodes connected to my pectoral muscle and I was adjusting the levels while holding up my arm with my hand to the side of my head. A random current change translated to a huge voltage boost, the pectoral twitched hard, and BLAMMO, punched myself in the bridge of the nose. At least I think that's what happened. Could have been changing skin conductivity, but I like to think my Teensy code hurt me. (I eventually removed the MCU and just used two comparitors with a voltage-controlled duty cycle oscillator... much easier.)