ADC Introduction

The ADC subsystem consists of a signal multiplexer and a voltage analog-to-digital converter (VADC), which is designed to route internal and external analog signals to the VADC via multiplexing and complete the conversion from analog quantities to digital quantities.

ADC Module hardware Architecture Diagram

ADC supported by the module

M1 The ADCs supported by the module are as follows:

Interface	Pin Number	Pin Name	PM4250 Pin Number	Voltage Domain	MPM Interrupt	Pin Description
ADC	128	ADC0	GPIO4	1.8 V	-	PMU_GPIO04
ADC	185	ADC1	GPIO7	1.8 V	-	PMU_GPIO07

L1 The ADCs supported by the module are as follows:

Interface	Pin Number	Pin Name	PM4250 Pin Number	Voltage Domain	MPM Interrupt	Pin Description
ADC	128	ADC0	PMU_GPIO06	1.8 V	-	PMU_GPIO04

M1/L1 ADC position

The position of the ADC interface on the intelligent main control board is shown in the following figure:

The position of the ADC on the intelligent main control board

Usage Example of ADC Node

The ADC node is mainly used to view the ADC value input to this node.

Instructions for use

An adjustable DC power supply shall be used as the input signal source during the test:

• Connect the power supply positive terminal to the ADC0 or ADC1 pin.

• Power supply GND is connected to the GND of the intelligent main control board.

M1： The corresponding relationship of each channel and input characteristics are as follows:

• ADC0：

  • Connect to GPIO4

  • 节点：in_voltage_adc_gpio4_input

  • Supported input voltage range: approx. 0~5.25 V

• ADC1：

  • Connect to GPIO7

  • 节点：in_voltage_adc_gpio7_input

  • Supported input voltage range: approx. 0~5.25 V

After setting the output of the DC power supply to the target voltage, the ADC sampling result (unit: μV) can be read via the following command:

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

ADC Read Example Output

L1: The channel correspondence and input characteristics are as follows:

• ADC0：

  • Connect to PMU_GPIO6

  • 节点：in_voltage_adc_gpio6_input

  • Supported input voltage range: approx. 0~5.25 V

After setting the output of the DC power supply to the target voltage, the ADC sampling result (unit: μV) can be read via the following command:

adb shell
cd /sys/bus/iio/devices/iio:device1
cat in_voltage_adc_gpio6_input

Test Code

The following sample code demonstrates the basic method of reading ADC voltage values in an application. The program reads the raw ADC value (in μV) by accessing the node file corresponding to the ADC, and converts it into an integer for subsequent processing.

Click to expand/collapse: ADC reading test code (can be compiled via NDK by yourself)

#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 into an integer (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; 
}

#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 PMU_GPIO6)
    fd = open("/sys/bus/iio/devices/iio:device1/in_voltage_adc_gpio6_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 into an integer (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; 
}

Code Description:

• Use open () function to open the ADC node file /sys/bus/iio/devices/iio: device0/in_voltage_adc_gpio4_input.

• Use read () function to read the raw ADC value (in string format, unit: μV).

• Use the atol () function to convert a string to a long integer value.

• The unit of the read ADC value is microvolts (μV), which can be converted into a voltage value as required.

Compile and run:

# Compile with NDK # Push the compiled executable file 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 pin definitions on the module are as follows:

Interface	Module Pin Number	Module Pin Name	Module I/O	NET Name (Multiplexing Function)	Description
ADC	128	ADC0	I	ADC0	1) Connector input voltage range: 0–5.25 V. 2) Voltage dividing resistors: RH = 18 kΩ, RL = 10 kΩ. 3) ADC pin voltage = connector input voltage (J0403) ×(10/28). 4) Example: When the input is 3 V, the voltage at the ADC pin shall be 3 V × 10/28 ≈ 1.0714 V.
ADC	185	ADC1	I	ADC1	Same electrical characteristics as ADC0 (0–5.25 V input range, RH = 18 kΩ, RL = 10 kΩ, ADC pin voltage = Vin × 10/28).

ADC0 Test Data

Voltage Source	ADC0（μV）	Theoretical Value (V)
1.8 V	638408	1.8 V×10/28 = 0.642857
3 V	1066414	3 V×10/28 = 1.07143
5 V	1784623	5 V×10/28 = 1.78571

ADC1 Test Data

Voltage Source	ADC1（μV）	Theoretical Value (V)
1.8 V	640549	1.8 V×10/28 = 0.642857
3 V	1069269	3 V×10/28 = 1.07143
5 V	1789814	5 V×10/28 = 1.78571