AnalogInput4.cpp

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#include <stdio.h>
#include <unistd.h>

#include "../hubolib.h"

using namespace HuboLib;

/*
Compile and link: 
    g++ AnalogInput4.cpp -L../ -lhubo -lpthread -lrt -o AnalogInput4.out
Run:
    sudo ./AnalogInput4.out
Purpose:
    Check and - if required - adjust the reference voltage of the MCP3208.
    The reference voltage should only be adjusted once the TL431 reference voltage has been measured with a high 
    precision instrument.
*/

int main(void)
{
    // Initialize the library once in your program.
    if (!Initialize())
    {
        printf ("Error: Initialize\n");
        return 1;
    }
    
    // Define channel 0 to be oversampled 40 times (set to 40) all other channels (set to 0) are not read from the ADC.
    unsigned short overSampling[MAX_MCP3x08_CHANNELS] = { 1, 0, 0, 0, 0, 0, 0, 0 };
    Set_MCP3x08_Oversampling (overSampling);

    // Let the AD buffers get filled.
    usleep(100000);

    // Check the current setting of the reference voltage of the TL431.
    printf ("VRef=%lf\n", Get_VRef());
        
    int             channel = 0;
    unsigned long   adcCount; 
    double          volt;
    
    // Read channel 0 and output its count as well as it's voltage value.
    Get_AI_Channel (channel, adcCount, volt);
    printf ("Channel=%d   ADC count=0x%02lX   Volts=%lf\n", channel, adcCount, volt);

    // Latch some more values...
    usleep(1000000);

    // Usually the reference voltage would be around 2.51V +-2%. So this value would be entered here.
    // However, let's see what happens if we'd use a value that is twice as big as the actual reference voltage.
    Set_VRef (2*Get_VRef());
    printf ("VRef=%lf\n", Get_VRef());

    // Read channel 0 and output it's count as well as its voltage value.
    Get_AI_Channel (channel, adcCount, volt);
    printf ("Channel=%d   ADC count=0x%02lX   Volts=%lf\n", channel, adcCount, volt);

    // Conclusion: While adjusting the reference voltage directly impacts the output value of the calculated voltage it 
    // does of cause not impact the measured ADC count. Setting VRef also does not alter the buffered values.
    // Since the setting refers to the TL431 it does affect all of the analog channels.
    
    // Free library resources.
    Uninitialize();
    
    return 0;
}