samedi 6 avril 2013

ADC with STM32F4

In many embedded projects, we have to deal with signals directly from nature, like temperature, pressure, current, etc... Theses signals are analog by default and in most of cases we use sensors that converts these analog signals to analog electrical voltage to be injected in the microcontroller to do some work.
Unfortunately, microcontrollers are digital and just can't deal with analog signals so these signals must be converted again to digital signals that is comprehensible by the microcontroller.

For this purpose, microcontroller's manufacturers usually incorporate an ADC into the microcontroller. ADC is actually stands for Analog to Digital Converter. This module is omnipresent in most of microcontrollers.

I'm going to use the STM32F4 discovery board to interface an analog input provided by a potentiometer and visualize the received data with the watch feature while debugging the program.

#include "stm32f4xx_adc.h"
#include "stm32f4xx_gpio.h"
#include "stm32f4xx_rcc.h"

int ConvertedValue = 0; //Converted value readed from ADC


void adc_configure(){
 ADC_InitTypeDef ADC_init_structure; //Structure for adc confguration
 GPIO_InitTypeDef GPIO_initStructre; //Structure for analog input pin
 //Clock configuration
 RCC_APB2PeriphClockCmd(RCC_APB2Periph_ADC1,ENABLE);//The ADC1 is connected the APB2 peripheral bus thus we will use its clock source
 RCC_AHB1PeriphClockCmd(RCC_AHB1ENR_GPIOCEN,ENABLE);//Clock for the ADC port!! Do not forget about this one ;)
 //Analog pin configuration
 GPIO_initStructre.GPIO_Pin = GPIO_Pin_0;//The channel 10 is connected to PC0
 GPIO_initStructre.GPIO_Mode = GPIO_Mode_AN; //The PC0 pin is configured in analog mode
 GPIO_initStructre.GPIO_PuPd = GPIO_PuPd_NOPULL; //We don't need any pull up or pull down
 GPIO_Init(GPIOC,&GPIO_initStructre);//Affecting the port with the initialization structure configuration
 //ADC structure configuration
 ADC_DeInit();
 ADC_init_structure.ADC_DataAlign = ADC_DataAlign_Right;//data converted will be shifted to right
 ADC_init_structure.ADC_Resolution = ADC_Resolution_12b;//Input voltage is converted into a 12bit number giving a maximum value of 4096
 ADC_init_structure.ADC_ContinuousConvMode = ENABLE; //the conversion is continuous, the input data is converted more than once
 ADC_init_structure.ADC_ExternalTrigConv = ADC_ExternalTrigConv_T1_CC1;// conversion is synchronous with TIM1 and CC1 (actually I'm not sure about this one :/)
 ADC_init_structure.ADC_ExternalTrigConvEdge = ADC_ExternalTrigConvEdge_None;//no trigger for conversion
 ADC_init_structure.ADC_NbrOfConversion = 1;//I think this one is clear :p
 ADC_init_structure.ADC_ScanConvMode = DISABLE;//The scan is configured in one channel
 ADC_Init(ADC1,&ADC_init_structure);//Initialize ADC with the previous configuration
 //Enable ADC conversion
 ADC_Cmd(ADC1,ENABLE);
 //Select the channel to be read from
 ADC_RegularChannelConfig(ADC1,ADC_Channel_10,1,ADC_SampleTime_144Cycles);
}
int adc_convert(){
 ADC_SoftwareStartConv(ADC1);//Start the conversion
 while(!ADC_GetFlagStatus(ADC1, ADC_FLAG_EOC));//Processing the conversion
 return ADC_GetConversionValue(ADC1); //Return the converted data
}
int main(void){
 adc_configure();//Start configuration
    while(1){//loop while the board is working
     ConvertedValue = adc_convert();//Read the ADC converted value
    }
}