How to Read SAR ADC Values on AML-S905X-CC

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1

There are 2 SAR ADC inputs reading up to 1.8V on the 2J8 header behind the HDMI port.
The SAR ADC values can be found in the following files:

cat /sys/bus/iio/devices/iio:device0/in_voltage0_raw
cat /sys/bus/iio/devices/iio:device0/in_voltage2_raw

They can be used for keypads, temperature sensing, and more but make sure to not exceed 1.8V.

2

man, Libre Computer is so cool. i love how you guys are building up the documentation. it is very impressive!

3

We are just documenting standard Linux interfaces. These methods have existed for years but the popular fruit Pi libraries promote other non-standard interfaces.

4

What data rate can I use these ADC’s at? Can I use them for audio input?

5

You can find info for the SARADCs on the public datasheets on Google. These are not designed for audio.

6

I have an array of AML-S905X-CC-V1.0-A “Le Potato” systems deployed remotely using BUSTER. We’d like to use the SARADC0 pin but after a few thousand file opens to read the system file, the system runs out of resources (sockets, etc) and only recovers when rebooted. Any help would be appreciated. A sample program demonstrates.

#include <stdio.h>
#include <stdlib.h>

int main(int argc, char **argv)
{
        FILE    *saradc_file = NULL;
        char    string[80];
        int     reg_value;
        int     counter = 0;

        while(1)
        {
                counter++;
                saradc_file = fopen("/sys/bus//iio/devices/iio:device0/in_voltage0_raw","r");
                if(saradc_file==NULL)
                   printf("Failed to open SARADC system file for read.   counter:%d\n",counter);

                if(fgets(string,80,saradc_file))
                {   reg_value = atoi(string);
                    printf("%d  Val: %d\n",counter,reg_value);
                }
                else printf("NO DATA TO READ\n");

                fclose(saradc_file);
        }
}