De Arduino series traditionally has an LED on digital Pin13, and the Blink program is usually the first program people use on their Arduino, kust to see if it works.
The disavantage of the LED that is coupled via a 1 k resistor is that it can disturb the function of the Pin as an input. There are basically 3 options to solve this program if you are building your own Arduino:
- Leave out the LED all together
- Connect it via a jumper
- Connect it via a FET
Ofcourse leaving it out will mean some loss of compatibility with the Arduino
Connecting it via a jumper may require some fiddling, especialy when the board is already built into a casing, also you may lose the jumper. Using a FET however is care free. The gate of a FET has a high impedance so it wil not load the pin when used as an input.