Analog Out Serial Sketch, Arduino for Dummies, Page 116 (MVI 8025)
Analog Out Serial Sketch, Arduino for Dummies, Page 116.
The variable resistor reading is used to control the brightness of the LED. Output pin 9 which is a PWM (Pulse Width Modulation) pin is used to control the brightness of the LED. PWM is the method of high speed switching off and on to provide the appearance of a variable current. The Arduino (Atmel ATMega 328PU chip) provides some pins that are PWM enabled, the chip handling the switching so the program only has to provide a number symbolic ie 0 to 255. 0 equals off and 255 equals bright.
The range of the LED is 0 to 255 but the variable resistor is 0 to 1023.
The C function 'map' is used to return a value from 0 to 255 when reading a value from 0 to 1023. This is basically a percentage conversion ie. 50% of 0 to 1023 is 600, 50% of 0 to 255 is around 127.