void analogReference (uint8_t type)
Configure the reference voltage
Configure the reference voltage of the mode pin. 函数 analogRead, after reading the analog value, will transform it to one during [0,1023], according to the reference voltage. There are the following types:
DEFAULT : 5V by default. INTERNAL: low consumption mode. ATmega168 and ATmega8 is corresponding to 1.1V to 2.56V. EXTERNAL: Expansion mode. Get reference voltage through AREF pin.
type reference type(DEFAULT/INTERNAL/EXTERNAL)