Wilmer
Wilmer
. 6 min read

Reading an analog voltage from a potentiometer in the BeagleBone Black

Reading an analog voltage from a potentiometer in the BeagleBone Black

In this post, I show a simple application to read and analog voltage with the ADC C++ class implementation shown previously in this post. Remembering that the BeagleBone has 7 analog inputs and ADC of 12 bits that let to de user to represent an analog signal within a range of 4096 values. It is important to remember that the reference for analog voltage is 1.8V. If the user provides a greater voltage, the BeagleBone could be damaged.

Circuit and components

The circuit can be seen in Figure 1. It consists of a Potentiometer with a power supplied using the analog ground pin 0V located at the pin P9_34 and to analog VDD pin at 1.8V located at the pin P9_32. Finally, its output is connected to the P9_39 pin.

The components are:

  • 1 Potentiometer of 200KΩ
  • Jumpers male-male to make the connections
Circuit.jpg
Figure 1: Circuit to read an analog value from a potentiometer in the BeagleBone

Coding

First an ADC class object is declared, for example:

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ADC adcPin(P9_39);

A float variable is declared and initialized to store the analog voltage.

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float adcVoltage = 0.0;

The voltage values can be obtained through the next class method:

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adcVoltage = adcPin.ReadVoltage();

In this case, the readings are taken through a user-defined function that runs on the background from the main program until a key from the keyboard will be pressed. It can be attached to the pin through the next method:

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adcPin.DoUserFunction(&AnalogRead);

This callback type function can be a while loop which reads not only the analog voltage but the digital value too. For example:

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int AnalogRead()
{
  while (stopAnalogRead == false)
  {
    adcValue = adcPin.ReadADC();
    cout << "ADC value on pin: " << adcValue << endl;
    adcVoltage = adcPin.ReadVoltage();
    cout << "Voltage on the pin: " << adcVoltage << endl;
    adcPin.Delayms(100);
  }
  return 0;
}

An aspect to take into account is the declaration of global variables in order to make it possible this function works.

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// Global variables
bool stopAnalogRead = false;
int adcValue = 0;
float adcVoltage = 0.0;

The complete code for this application is shown in the next listing together with its corresponding execution video.

Listing_5.2

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#include <iostream>
#include "../../Sources/ADC.h"

using namespace std;

// Global ADC pin declaration 
ADC adcPin(P9_39);

// Global variables
bool stopAnalogRead = false;
int adcValue = 0;
float adcVoltage = 0.0;
int AnalogRead()
{
  while (stopAnalogRead == false)
  {
    adcValue = adcPin.ReadADC();
    cout << "ADC value on pin: " << adcValue << endl;
    adcVoltage = adcPin.ReadVoltage();
    cout << "Voltage on the pin: " << adcVoltage << endl;
    adcPin.Delayms(100);
  }
  return 0;
}

int main()
{
  string message = "Main program starting here...";
  cout << RainbowText(message,"Blue", "White", "Bold") << endl;

  // Call the function to read the pin
  adcPin.DoUserFunction(&AnalogRead);

  char userInput = '\0';
  while (userInput != 'y')
  {
    message = "Do you want to stop the readings on the pin? Enter 'y' for yes: ";
    cout << RainbowText(message, "Blue")  << endl;
    cin >> userInput;
    if (userInput == 'y') 
    {
      stopAnalogRead = true;
      adcPin.StopUserFunction();
    }
  }

  message = "Main program finishes here...";
  cout << RainbowText(message,"Blue", "White","Bold") << endl;

  return 0;
}

Execution of the program:

Video: Execution of the program.

Se you in the next post.

Rating:
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