12Bit ADC(MCP3208)

SPI / By /

Sometime 10bit ADC is not enough for precious calculation. In that case we have 12bit ADC i.e. MCP3208.

SPI Configuration

Here B11-B0 is the 12bit ADC value. Thus the operating logic consist of MCP3208 consists of following steps-

Let’s use two function one is only write and other is read-write.

  1. void SPIWrite(uint8_t input) -> Only SPI write
void SPIWrite(uint8_t input)
{
SPDR=input;
while(!(SPSR&(1<<SPIF)))
	{
	;//wait until transmission complete
	}
}
  1. uint8_t SPIReadWrite(uint8_t input) -> Both SPI write and read function
uint8_t SPIReadWrite(uint8_t input)
{
SPDR=input;
while(!(SPSR&(1<<SPIF)))
	{
	;//wait until transmission complete
	}
return(SPDR);
}

So the full user-defined function for ADC read as follow-

uint16_t READAdc(uint8_t ch)
{
	uint8_t dataHIGH,dataLOW,bytestream;
	SPI_PORT&=~(1<<SPI_CS);     //enable latch
	bytestream=0b00000110;
	if(ch>3)
		{
		bytestream=0b00000111;
		}
	SPIWrite(bytestream);
	bytestream=(ch<<6);
	dataHIGH=SPIReadWrite(bytestream); //send any bit to receved data
	dataHIGH&=0b00001111;              //4bit high value
	dataLOW=SPIReadWrite(0xff);        //send any bit to receved data
	SPI_PORT|=(1<<SPI_CS);             //disable latch
	return((dataHIGH<<8)|(dataLOW));
}

Let’s make a Temperature meter with 12 bit ADC. If we use LM35 then it gives 10millivolts per degree centigrade. Since we use 12bit ADC than the resolution should be-

            Resolution=5/212 =1.2207mV

So the Temperature = (12bit ADC return value) x 0.12207

Download the mcp3208.c & mcp3208.h file and the main program as follow-

#include<avr/io.h>
#include<stdio.h>
#include"mcp3208.h"
#include"lcd.h"
int main(void)
{
LCD_INIT();
ADCInitx();
float temp;
uint16_t ADCValue;
char LCD[20];
LCD_write_string(1,1,"ADC result Display");
	while(1)
		{
			ADCValue=READAdc(3);
			temp=ADCValue*0.12207;
			sprintf(LCD,"Temperature=%.2f",(double)temp);
			LCD_write_string(1,2,LCD);
		}
return 0;
}
download

12-bit ADC(MCP3208).rar