If the board powers off during an SD card write cycle the card could get trashed. We need to add a big decoupling capacitor (470 uF) on the 3.3V line so that the SD card has enough time to finish a write cycle. Make sure at power-down the cap charge can't get sucked back through the power supply, so a diode upstream, or make sure there's protection on the output of the 3.3V circuitry. We should also include digital input to a MCU pin upstream of the capacitor that we can check before a write cycle. If the power is bad that pin will be low and we won't open and write, otherwise the cap should have enough charge in it to finish the cycle.
If the board powers off during an SD card write cycle the card could get trashed. We need to add a big decoupling capacitor (470 uF) on the 3.3V line so that the SD card has enough time to finish a write cycle. Make sure at power-down the cap charge can't get sucked back through the power supply, so a diode upstream, or make sure there's protection on the output of the 3.3V circuitry. We should also include digital input to a MCU pin upstream of the capacitor that we can check before a write cycle. If the power is bad that pin will be low and we won't open and write, otherwise the cap should have enough charge in it to finish the cycle.