Arduino Playground is read-only starting December 31st, 2018. For more info please look at this Forum Post An SPI library is now included in the Arduino software. See the SPI library reference for details. Why doesn't my LED turn on after starting SPI ? Why doesn't "digitalWrite(ledPin, HIGH);" work after starting SPI -- why doesn't my LED turn on? After executing "SPI.begin();", the command "digi