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[SOLVED] Multiple ADC channels

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fsoender

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I need some help with my project. Im reading a accelerometer with ADC on port PA0 on a Atmega16. Im reading only X-axes. I want to add Y and Z also, but I dont know how.
Im reading the input with TeraTerm, line by line downwards. I want the y and Z to be added on the side of the X value.
IM using AVR studio 4.

Can anyone help me with this?

Code: 
 #include<avr/io.h> 
#include<util/delay.h> 
#include<avr/interrupt.h> 
  


#define LONGOUT 7 
char buffer[LONGOUT]; 

void adc_init(void); 
unsigned int adc_read(void); 
void adc_conversion(uint16_t); 




// ADC configuration 
void ADC_init(void) { 
  ADMUX=(1<<REFS0); 
  ADCSRA=(1<<ADEN)|(7<<ADPS0); 
} 

uint16_t ADC_get_reading(void) { 
  ADCSRA |= (1<<ADSC); 
  while(ADCSRA & (1<<ADSC)); 
  return ADC; 
} 

uint16_t ADC_read(void) { 
  uint8_t i; 
  uint16_t retval = 0; 
  ADC_get_reading(); // dummy read - just discarded 
  for (i=0; i<8; i++) { 
    retval += ADC_get_reading(); 
  } 
  return retval / 8; 
} 


void init_UART(void) 
{ 
   UCSRB = ((1 << RXCIE) | (1 << RXEN) | (1 << TXEN)); 
    UCSRC = ((1 << UCSZ1) | (1 << UCSZ0)); 
    
    //Baud rate till 19200.  
    UBRRL = 25; 
    UBRRH = 0; 
} 


void uart_sendchar(char c) { 
   while(!(UCSRA & (1<<UDRE))); 
   UDR = c; 
} 

void uart_printstring(char * str) { 
  while (*str) { 
   uart_sendchar(*str++); 
  } 
} 


void main(void) { 
    
 DDRC = 0x00;    
 init_UART(); 
 ADC_init(); 
  
  
  while(1) 
  { 
    if (PINC & 0x01) //If PortC pin 0 is True, program stops. 
   { 
 ADC_read(); 
            
 char buffer[8]; 
 itoa(ADC, buffer, 10); 
 uart_printstring(buffer); 
 uart_printstring("\r\n"); 
 _delay_ms(1500); 
  
    } 
  } 
}
 

You can use this function, call it with the number of the channel you want to convert (0,1,2....)

Code C - [expand]
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/*****************************************************************************
** Function name:   read_adc    
**
** Descriptions:    makes an ADC measurment in the specified channel
**                  
** parameters:      unsigned char adc_input: channel number
** Returned value:  unsigned int: returns 0-1023
** 
*****************************************************************************/
unsigned int read_adc(unsigned char adc_input)
{
    // clear the channel bits ane set the new channel
    ADMUX =  (ADMUX & 0xF8) | adc_input;
    
    // Delay needed for the stabilization of the ADC input voltage
    _delay_us(10);
    
    // Start the AD conversion
    ADCSRA |= 0x40;
 
    // Wait for the AD conversion to complete
    while (ADCSRA & (1 << ADSC)) 
 
    // return result
    return ADCW;
}


just modify it to do 8 readings and return the average like you did in your code
 

Thanks!
Sorry im new to this, but how do I call it, and where in my program?
 

You call it from main.

In your current code you are calling ADC_read(); which in turn calls ADC_get_reading
Also in your code you don't store the result of ADC_read(); anywhere and you just use the ADC register value (last conversion result, not the calculated average)

If you use the code I have provided you can replace ADC_read(); with read_adc(x) where x is the channel number and store the result to the variables.

You are supposed to do
Code: 
uint16_t x,y,z;

x=read_adc(0); 
y=read_adc(1);
z=read_adc(2);
 

Thanks, That worked fine :)

My last question is:

Im now only displaying the X-axe on TeraTerm, I want all of the axes to show up like this with their values:

x-Value y-Value z-Value

xxxx xxxx xxxx
 

This is what makes the conversion and converts the values 0-1023 to four ascii characters in buffer[0] buffer[1] buffer[2] buffer[3]
Code: 
itoa(ADC, buffer, 10);

you cant to convert x to the above positions , y to buffer[5] buffer[6] buffer[7] buffer[8]
and z to buffer[10] buffer[11] buffer[12] buffer[13]

buffer needs to be bigger
Code: 
#define LONGOUT 15 
char buffer[LONGOUT]="0000 0000 0000";

itoa(x, buffer, 10);
itoa(y, &buffer[5], 10);
itoa(z, &buffer[10], 10);

then send buffer to uart
 

I didnt get it to work, see any misstake(s):

Code: 
#include<avr/io.h> 
#include<util/delay.h> 
#include<avr/interrupt.h> 
  


#define LONGOUT 15 
char buffer[LONGOUT]="0000 0000 0000";
 

void adc_init(void); 
unsigned int adc_read(void); 
void adc_conversion(uint16_t); 

unsigned char x;
unsigned char y;
unsigned char z;


// ADC configuration 
void ADC_init(void) { 
  ADMUX=(1<<REFS0); 
  ADCSRA=(1<<ADEN)|(7<<ADPS0); 
} 

uint16_t ADC_get_reading(void) { 
  ADCSRA |= (1<<ADSC); 
  while(ADCSRA & (1<<ADSC)); 
  return ADC; 
} 

unsigned int read_adc(unsigned char adc_input)
{
    // clear the channel bits ane set the new channel
    ADMUX =  (ADMUX & 0xF8) | adc_input;
    
    // Delay needed for the stabilization of the ADC input voltage
    _delay_us(10);
    
    // Start the AD conversion
    ADCSRA |= 0x40;
 
    // Wait for the AD conversion to complete
    while (ADCSRA & (1 << ADSC)) 
 
    // return result
    return ADCW;
}


void init_UART(void) 
{ 
   UCSRB = ((1 << RXCIE) | (1 << RXEN) | (1 << TXEN)); 
    UCSRC = ((1 << UCSZ1) | (1 << UCSZ0)); 
    
    //Baud rate till 19200.  
    UBRRL = 25; 
    UBRRH = 0; 
} 


void uart_sendchar(char c) { 
   while(!(UCSRA & (1<<UDRE))); 
   UDR = c; 
} 

void uart_printstring(char * str) { 
  while (*str) { 
   uart_sendchar(*str++); 
  } 
} 


void main(void) { 
    
 DDRC = 0x00;    
 init_UART(); 
 ADC_init(); 
  
  
  while(1) 
  { 
    
x=read_adc(0); 
y=read_adc(1);
z=read_adc(2);
            
 char buffer[8];
 itoa(x, buffer, 10);
 itoa(y, &buffer[5], 10);
 itoa(z, &buffer[10], 10);
 
  
 uart_printstring(buffer); 
 uart_printstring("\r\n"); 
 _delay_ms(1500); 
  
    } 
  }
 

You have a global variable
Code: 
char buffer[LONGOUT] = "0000 0000 0000";

and then you add a local variable that hides the visibility of the global one and in adition has a wrong length, remove it
Code: 
char buffer[8];
 

Oh, my misstake, but it still doesnt work.
Is rest of the code right?
I still only get one column with value...
 

Yes, itoa adds a null after the result

A quick fix is

Code: 
#define LONGOUT 15 
char buffer[LONGOUT]="0000 0000 0000";

itoa(x, buffer, 10);
buffer[4]=' ';
itoa(y, &buffer[5], 10);
buffer[9]=' ';
itoa(z, &buffer[10], 10);
 

That didnt help either, it still gives me only one column in TeraTerm.
 

Now I'm not sure why.

By one column you mean the x value, 4 digits?

- - - Updated - - -

Add
Code: 
#include <stdio.h>

//and use
sprintf(buffer,"%.4u %.4u %.4u ",x,y,z);

I think the problem was the variable width of the result generated by the itoa, the null character was not always in the same location
 

Yes I want one coulmn with x value, one with y value and one with z value:

0000 0000 0000
0000 0000 0000

and so on...

Sorry, but I cant get this to work. Am I missing something here?

Code: 
while(1) 
  { 
    
x=read_adc(0); 
y=read_adc(1);
z=read_adc(2);
            
 
itoa(x, buffer, 10);
buffer[4]=' ';
itoa(y, &buffer[5], 10);
buffer[9]=' ';
itoa(z, &buffer[10], 10);
 
sprintf(buffer,"%.4u %.4u %.4u ",x,y,z);
 //uart_printstring(buffer); 
 //uart_printstring("\r\n"); 
 _delay_ms(1500); 
  
    } 
  }
 
Last edited:

remove all this
Code: 
itoa(x, buffer, 10);
buffer[4]=' ';
itoa(y, &buffer[5], 10);
buffer[9]=' ';
itoa(z, &buffer[10], 10);

I have replaced the three itoa with the sprintf

- - - Updated - - -

and uncomment the uart

- - - Updated - - -

the sprintf just converts the three values to ascii and writes the buffer array, you still need the uart function to send then to the pc
 

That worked :)

Thank you so much for your time and help Alexan_e!!!

- - - Updated - - -

Next now is to read the ADC 8 times and get the average value, any suggestions?
 

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