ADC overview

The ADC subsystem consists of a signal multiplexer and a voltage analog-to-digital converter (VADC). It routes internal and external analog signals to the VADC through a multiplexed architecture and converts them into digital values.

ADC module hardware architecture

Supported ADC channels

The module supports the following ADC channels:

ADC interface location

The location of the ADC interface on the smart main control board is shown below:

ADC interface location on the smart main control board

ADC node usage example

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

Usage method

For testing: 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.
• Connect the power supply ground (GND) to the GND of the smart main control board.

Channel mapping and input characteristics are as follows:

• ADC0:
  • Mapped to GPIO4
  • Corresponding node: in_voltage_adc_gpio4_input
  • Supported input voltage range: Approximately 0–5.25 V.
• ADC1:
  • Mapped to GPIO7
  • Corresponding node: in_voltage_adc_gpio7_input
  • supported input voltage range: Approximately 0–5.25 V.

After setting the DC power supply to the desired voltage, the ADC sampling result can be read using the following commands (unit: μV):

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

Sample 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