STM32F4 Discovery Tutorial 7 - ADC

In this tutorial, I will share how to use ADC on STM32F4 Discovery to read analog voltage. ADC is stands for Analog to Digital Converter. Microcontrollers are digital component, so they only understand discrete/digital signals. Therefore if you want to read analog voltage that can be from various sensors, you need an ADC. STM32F407 has 3 ADC that can work independently. Every ADC have 18 channels. 16 channels are external and connected to GPIO pin. 2 channels are internal that connected to internal temperature sensor and ADC voltage reference.

When you use ADC, you can choose which ADC and its channel from this table:

Once you have select which ADC and its pin that you want to use, you can start to coding. In this example, I will use ADC1 on channel 9 (PB1). I will connect trimpot to PB1 as a source for analog input voltage. 

This is code for setup ADC. I made this code on a function called ADC_Config().

void ADC_Config(void)
{
    // Enable clock for ADC1
    RCC_APB2PeriphClockCmd(RCC_APB2Periph_ADC1, ENABLE);

    // Init GPIOB for ADC input
    GPIO_InitTypeDef GPIO_InitStruct;
    GPIO_InitStruct.GPIO_Mode = GPIO_Mode_AN;
    GPIO_InitStruct.GPIO_Pin = GPIO_Pin_1;
    GPIO_InitStruct.GPIO_PuPd = GPIO_PuPd_NOPULL;
    GPIO_Init(GPIOB, &GPIO_InitStruct);

    // Init ADC1
    ADC_InitTypeDef ADC_InitStruct;
    ADC_InitStruct.ADC_ContinuousConvMode = DISABLE;
    ADC_InitStruct.ADC_DataAlign = ADC_DataAlign_Right;
    ADC_InitStruct.ADC_ExternalTrigConv = DISABLE;
    ADC_InitStruct.ADC_ExternalTrigConvEdge = 
        ADC_ExternalTrigConvEdge_None;
    ADC_InitStruct.ADC_NbrOfConversion = 1;
    ADC_InitStruct.ADC_Resolution = ADC_Resolution_12b;
    ADC_InitStruct.ADC_ScanConvMode = DISABLE;
    ADC_Init(ADC1, &ADC_InitStruct);
    ADC_Cmd(ADC1, ENABLE);

    // Select input channel for ADC1
    // ADC1 channel 9 is on PB1
    ADC_RegularChannelConfig(ADC1, ADC_Channel_9, 1, 
        ADC_SampleTime_84Cycles);
}

This is the function for read ADC value:

uint16_t ADC_Read(void)
{
    // Start ADC conversion
    ADC_SoftwareStartConv(ADC1);
    // Wait until conversion is finish
    while (!ADC_GetFlagStatus(ADC1, ADC_FLAG_EOC));

    return ADC_GetConversionValue(ADC1);
}

This is the full code of this tutorial. In the main program, ADC1 reads the value of trimpot that connected to PB1 every 1s then send it to PC via USART1. Here I used three library that I made from previous tutorial for setting clock to 168MHz, delay using SysTick timer, and USART.

#include "stm32f4xx.h"
#include "stm32f4xx_rcc.h"
#include "stm32f4xx_gpio.h"
#include "stm32f4xx_adc.h"
#include "clock.h"
#include "delay.h"
// USART library (USART1 on PB6 and PB7)
#include "usart.h"
#include <stdio.h>

// For ADC value
uint16_t adcValue = 0;
// For ADC value in string
char sAdcValue[5];

void ADC_Config(void)
{
    // Enable clock for ADC1
    RCC_APB2PeriphClockCmd(RCC_APB2Periph_ADC1, ENABLE);

    // Init GPIOB for ADC input
    GPIO_InitTypeDef GPIO_InitStruct;
    GPIO_InitStruct.GPIO_Mode = GPIO_Mode_AN;
    GPIO_InitStruct.GPIO_Pin = GPIO_Pin_1;
    GPIO_InitStruct.GPIO_PuPd = GPIO_PuPd_NOPULL;
    GPIO_Init(GPIOB, &GPIO_InitStruct);

    // Init ADC1
    ADC_InitTypeDef ADC_InitStruct;
    ADC_InitStruct.ADC_ContinuousConvMode = DISABLE;
    ADC_InitStruct.ADC_DataAlign = ADC_DataAlign_Right;
    ADC_InitStruct.ADC_ExternalTrigConv = DISABLE;
    ADC_InitStruct.ADC_ExternalTrigConvEdge = 
        ADC_ExternalTrigConvEdge_None;
    ADC_InitStruct.ADC_NbrOfConversion = 1;
    ADC_InitStruct.ADC_Resolution = ADC_Resolution_12b;
    ADC_InitStruct.ADC_ScanConvMode = DISABLE;
    ADC_Init(ADC1, &ADC_InitStruct);
    ADC_Cmd(ADC1, ENABLE);

    // Select input channel for ADC1
    // ADC1 channel 9 is on PB1
    ADC_RegularChannelConfig(ADC1, ADC_Channel_9, 1, 
        ADC_SampleTime_84Cycles);
}

uint16_t ADC_Read(void)
{
    // Start ADC conversion
    ADC_SoftwareStartConv(ADC1);
    // Wait until conversion is finish
    while (!ADC_GetFlagStatus(ADC1, ADC_FLAG_EOC));

    return ADC_GetConversionValue(ADC1);
}

int main(void)
{
    // Set clock to 168MHz
    // Don't forget to add defined symbol "HSE_VALUE=8000000"
    // in compile configuration
    CLOCK_SetClockTo168MHz();
    // Init delay function
    DELAY_Init();
    // Init USART
    // Here I'm using USART1 (PB6 Tx, PB7 Rx)
    USART_Config();
    // ADC config
    ADC_Config();

    while (1)
    {
        // Read ADC value
        adcValue = ADC_Read();
        // Convert to string
        sprintf(sAdcValue, "%i\n", adcValue);

        // Send to PC via USART1
        USART_PutString(sAdcValue);

        DELAY_Ms(1000);
    }
}

This is the link for download these 3 library: clock, delay, and usart.