Raspberry Pi SD Card Corruption

There are stories on the web about this issue and I have experienced it myself now. Twice.

The issue seems to occur when the device is powered off when accessing the SD Card. Exactly what the damage is is not clear though. The Pi boots and displays many file system errors. The first time this occurred, after the usual fsck attempts, I decided to build the machine again on another SD Card. The second time it occurred I tried something new. I used my Linux machine to dd the SD Card content to another identical SD Card. There were no read errors and no write errors on the first SDCard which was from the first build.

My assumption is that at some point on the file system a low voltage event has occurred that has set a low value in one of the flash nodes. Research required on my part to understand the flash storage and access circuitry but it seems to work fine when read and written to from my laptop and via a USB flash adapter.

So the flash just needed to be completely read and rewritten.

So I have now added a shutdown button. This will shutdown the Pi when the button is depressed for six seconds. There are many examples of how this is done on the web but none apply to the Pi 3B+.

Using a switch over pins 39 and 40 of the GPIO is called GPIO 21.

LEDS to indicate activity such as flashing can be controlled via system commands to echo values to /sys/class/leds/led1/trigger and delay_on and delay_off when trigger is set to timer.