On first glace, the pinout of the microSD or SD card is anything but complicated. An engineer with minimal experience would have no problem figuring out the which pin does what. A typical microSD consumes up to 100mA at 3.3V, so obviously nothing would go wrong when I connected it to a 3.3V supply. At least that’s what I thought until I re-inserted the SD card in my working prototype. I, like many engineers before me, neglected an important concept when designing circuitry for an SD interface. We did not take the in-rush current into consideration. This resulted in our microcontroller resetting itself every time an SD card was inserted into it.