Lesson 11 Voltmeter

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Introduction

In this lesson, we will use a Raspberry Pi and an ADC0832 to make a voltmeter.

Experimental Conditions

– 1*Raspberry Pi

– 1*Breadboard

– 1*Network cable (or USB wireless network adapter)

– 1*ADC0832

– 1*Potentiometer

– Jumper wires

Experimental Principle

In this experiment, we use the potentiometer to divide voltage.

Since the Raspberry Pi can only read digital signals, but what the adjusting end of the potentiometer outputs is an analog signal, so we need to convert the analog signal into digital signal with an ADC (Analog to Digital Convertor). Then we make this digital output voltage display on the screen.

Experimental Procedures

Step 1: Connect the circuit as shown in the following diagram

Step 2: Edit and save the code (see path/Rpi_UniversalStartKit /11_voltmeter/vol.c)

Step 3: Compile the code

gcc vol.c -lwiringPi

Step 4: Run the program

./a.out

Press Enter, if you adjust the potentiometer , you will see the voltage value displayed on the screen changed.

vol.c

#include <wiringPi.h>
#include <stdio.h>

typedef unsigned char uchar;
typedef unsigned int  uint;

#define     ADC_CS    0
#define     ADC_CLK   1
#define     ADC_DIO   2

uchar get_ADC_Result(void)
{
 //10:CH0
 //11:CH1
 uchar i;
 uchar dat1=0, dat2=0;

 digitalWrite(ADC_CS, 0);

 digitalWrite(ADC_CLK,0);
 digitalWrite(ADC_DIO,1); delayMicroseconds(2);
 digitalWrite(ADC_CLK,1); delayMicroseconds(2);
 digitalWrite(ADC_CLK,0);

 digitalWrite(ADC_DIO,1);    delayMicroseconds(2); //CH0 10
 digitalWrite(ADC_CLK,1); delayMicroseconds(2);
 digitalWrite(ADC_CLK,0);

 digitalWrite(ADC_DIO,0); delayMicroseconds(2); //CH0 0
 
 digitalWrite(ADC_CLK,1);
 digitalWrite(ADC_DIO,1);    delayMicroseconds(2);
 digitalWrite(ADC_CLK,0);
 digitalWrite(ADC_DIO,1);    delayMicroseconds(2);
 
 for(i=0;i<8;i++)
 {
  digitalWrite(ADC_CLK,1); delayMicroseconds(2);
  digitalWrite(ADC_CLK,0);    delayMicroseconds(2);

  pinMode(ADC_DIO, INPUT);
  dat1=dat1<<1 | digitalRead(ADC_DIO);
 }
 
 for(i=0;i<8;i++)
 {
  dat2 = dat2 | ((uchar)(digitalRead(ADC_DIO))<<i);
  digitalWrite(ADC_CLK,1);  delayMicroseconds(2);
  digitalWrite(ADC_CLK,0);    delayMicroseconds(2);
 }

 digitalWrite(ADC_CS,1);

 pinMode(ADC_DIO, OUTPUT);
 
 return(dat1==dat2) ? dat1 : 0;
}

int main(void)
{
 uchar adcVal;
 float vol;

 if(wiringPiSetup() == -1){
  printf("setup wiringPi failed !");
  return 1;
 }

 pinMode(ADC_CS,  OUTPUT);
 pinMode(ADC_CLK, OUTPUT);

 while(1){
  pinMode(ADC_DIO, OUTPUT);
  adcVal = get_ADC_Result();
  printf("Current Voltage : %0.2f V\n", adcVal*(5.0/255));
 
  delay(400);
 }

 return 0;
}

Python Code

#!/usr/bin/env python
import ADC0832
import time

def init():
 ADC0832.setup()

def loop():
 while True:
  res = ADC0832.getResult()
  v = res * (3.3 / 255)
  print 'Current voltage: %.2f V' % v
  time.sleep(0.2)

if __name__ == '__main__':
 init()
 try:
  loop()
 except KeyboardInterrupt:
  ADC0832.destroy()
  print 'The end !'