2.3 Analog IO

2.3.1 void analogReference(type);

• brief: set analog reference voltage to a particular value according to different type.

  • DEFAULT: 5 Volt;

  • INTERNAL: 2.56 Volt

  • EXTERNAL: get the voltage value via AREF pin. There must be a 5K ohm pull-up resistor．

• param:

  • type: DEFAULT, INTERNAL or EXTERNAL.

• return: void.

2.3.2 int analogRead(pin);

• brief: read analog voltage from a particular pin, at a period about 100US.

• param:

  • pin: analog IO pin index, must be a value between 0 and 5, corresponding to analog pin A0 ~ A5.

• return: int, between 0 and 1023.

2.3.3 void analogWrite(pin, value);

• brief: write voltage value to pin, by PWM.

  • Arduino PWM is typically of frequency 490HZ.

  • On an Arduino UNO, digital pins 3, 5, 6, 9, 10, 11 with a ~ sign support PWM analog output.

  • PWM output is of 8 bits, namely, a value between 0 and 255.

• param:

  • pin: analog IO pin index, must be a value between 0 and 5, corresponding to analog pin A0 ~ A5.

  • value: HIGH or LOW, where HIGH is for high level voltage, LOW is for low level voltage.

• return: void.