BeagleBone Black ADC
The BeagleBone® Black hardware has six analog input pins (AIN0 to
AIN5). Each analog input pin has a 12-bit analog-to-digital
converter (ADC) that converts the analog input voltage to a digital voltage
reading.

In addition to the six input pins, the BeagleBone Black hardware has power rail and ground pins (VDD_ADC
and GND_ADC).
The function readVoltage measures the voltage applied to an analog
input pin relative to the ADC ground pin (GND_ADC). The ADC-driver
built into the Linux® kernel returns the voltage measurement converted to a double. The values
range from 0 V (GND_ADC) - 1.8
V (VDD_ADC).
Caution
Never connect a voltage greater than
1.8 Vacross the ADC pins. Voltages greater than1.8 Vcan damage the board.Always connect the negative (ground) side of a voltage source to
GND_ADC. The ADC measures positive voltages only. A reversed connection can damage the board.