ADC overview

The ADC subsystem includes signal multiplexing and a voltage analog-to-digital converter (VADC). It is a multiplexed network that routes internal and external signals to the VADC.

ADC module hardware architecture

Supported ADC channels

The module supports the following ADC channels:

ADC interface location

The location of the ADC interfaces on the smart single-board computer is shown below:

ADC location on the smart single-board computer

ADC node usage example

The ADC nodes are mainly used to read the ADC values at the corresponding input nodes.

Usage

Test method: use an adjustable DC power supply as the input signal source. Connect the positive terminal of the power supply to the ADC0 or ADC1 pin, and connect the power supply ground (GND) to the development board's GND.

• ADC0: connected to GPIO4, corresponding node in_voltage_adc_gpio4_input, supported input voltage range is approximately 0–5.25 V.
• ADC1: connected to GPIO7, corresponding node in_voltage_adc_gpio7_input, supported input voltage range is approximately 0–5.25 V.

After setting the DC power output to an arbitrary voltage, you can read the returned ADC value (in μV) using the following commands:

adb shell
cd /sys/bus/iio/devices/iio:device0
cat in_voltage_adc_gpio4_input
cat in_voltage_adc_gpio7_input

Example of ADC read output

Test code

The following sample code demonstrates how to read the ADC value in an application. It opens the ADC node file, reads the raw ADC value (in μV), and converts it to an integer for further processing.

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <fcntl.h>
#include <string.h>
#include <errno.h>

int main() 
{ 
    int fd = -1; 
    int adc_value; 
    char buff[64] = {0}; 

    // Open the ADC node file (ADC0 corresponds to GPIO4)
    fd = open("/sys/bus/iio/devices/iio:device0/in_voltage_adc_gpio4_input", O_RDONLY);   
    if(fd < 0){ 
        perror("open error\n"); 
        return fd; 
    } 

    // Read the ADC value
    int n_read = read(fd, buff, sizeof(buff)); 
    if(n_read < 0) {
        perror("read error\n");
        close(fd);
        return -1;
    }

    // Convert the read string to an integer value (unit: μV)
    adc_value = atol(buff); 
    printf("read %d bytes, content: %s\n", n_read, buff); 
    printf("ADC value: %d μV\n", adc_value);   

    close(fd); 
    return 0; 
}

# Compile with NDK
# Push the compiled executable to the device and run it
adb push test_adc /data/local/tmp/test_adc
adb shell "chmod +x /data/local/tmp/test_adc"
adb shell "/data/local/tmp/test_adc"

Test data

ADC pin specifications

The ADC pins on the module are defined as follows:

ADC0 test data

ADC1 test data