When the green LED of your Raspberry PI does not flash, the system can’t successfully access the microSD card. So you are probably in one of the following situations:

1. You did not insert a preformatted and flashed microSD card
2. Your microSD card is corrupted, and does not work anymore

Solution:

You should always keep a copy of the ISO image of your operating system. If you don’t, please download one at http://downloads.raspberrypi.org/raspbian_latest

Flash a new microSD card with the OS (if the old one is corrupted, you should avoid using it again). You can use balenaEtcher: it’s free and has the same GUI for Linux, WIndows and MAC.

The microSD has three primary parameters:

• Memory capacity

• • MicroSD = up to 2 GB
  • MicroSDHC (High Capacity) = from 4 GB to 32 GB
  • MicroSDXC (eXtended Capacity) = from 64 GB to 2 TB

• UHS Speed class

• • MicroSD Class 2 = 2MB/s
  • MicroSD Class 4 = 4MB/s
  • MicroSD Class 6 = 6MB/s
  • MicroSD Class 10 = 10MB/s
  • MicroSD UHS-I 1 = 10 MB/s – Bus Speed 50-104 MB/s
  • MicroSD UHS-I 3 = 30 MB/s  – Bus Speed 50-104 MB/s
  • MicroSD UHS-II 1 = 10 MB/s  – Bus Speed 156-312MB/s
  • MicroSD UHS-II 3 = 30 MB/s – Bus Speed 156-312MB/s

• Video Speed Class – V6, V10, V30, V60, V90 again it’s the sequential write speed

So, the next time your system refuses to boot, check the green LED on your Raspberry PI and eventually flash a new ISO image. That’s all!

Arduino UNO R3.

Elegoo Arduino Starter kit.

Sandisk Extreme Memory card microSDHC 32 GB.

Sandisk Ultra Memory card microSDHC 16 GB,