ADC

Turn off M4 core

By default, ADC pins (A0-A5) are assigned to the M4 core, so they can be used by Arduino.

If you want, you can use the ADC pins from Linux; however you must disable the M4 core. Follow this guide to disable the M4 core startup.

Read ADC Data

You can read ADC values from virtual files in the sysfs:

/sys/bus/iio/devices/

UDOO Neo has ADC banks, adc1 and adc2:

adc1 -> /sys/bus/iio/devices/iio\:device0/
adc2 -> /sys/bus/iio/devices/iio\:device1/

The corresponding pin values are located in:

A0 ->  /sys/bus/iio/devices/iio\:device0/in_voltage0_raw
A1 ->  /sys/bus/iio/devices/iio\:device0/in_voltage1_raw
A2 ->  /sys/bus/iio/devices/iio\:device0/in_voltage2_raw
A3 ->  /sys/bus/iio/devices/iio\:device0/in_voltage3_raw
A4 ->  /sys/bus/iio/devices/iio\:device1/in_voltage0_raw
A5 ->  /sys/bus/iio/devices/iio\:device1/in_voltage1_raw

If you want to read the A0 pin numeric value, access its file:

cat /sys/bus/iio/devices/iio\:device0/in_voltage0_raw

If you want the analogic value expressed in millivolts instead of int, you can multiply the in_voltageX_raw file for the in_voltage_scale file

Example: read A0

The following examples read the A0 integer values, multiplies it for the ADC scale and prints the result to the console:

raw=$(</sys/bus/iio/devices/iio\:device0/in_voltage0_raw)
scale=$(</sys/bus/iio/devices/iio\:device0/in_voltage_scale)
echo "$raw * $scale" | bc -l 
3299.194333890

<?php
$raw = file_get_contents("/sys/bus/iio/devices/iio:device0/in_voltage0_raw");
$scale = file_get_contents("/sys/bus/iio/devices/iio:device0/in_voltage_scale");
echo $raw*$scale . PHP_EOL;

raw = int(open("/sys/bus/iio/devices/iio:device0/in_voltage0_raw").read())
scale = float(open("/sys/bus/iio/devices/iio:device0/in_voltage_scale").read())

print raw*scale

Precision

Analog inputs have a 12 bit precision (from 0 to 4095)