“UART Based Temperature Monitoring with STM32F401C and LM35”

#include "stm32f4xx.h"         // CMSIS header for STM32F4 - gives access to all peripheral registers
#include <stdint.h>            // For standard integer types like uint16_t
#include <stdio.h>             // For sprintf() to format strings (must enable float support if using with float)

// Constant for delay (approx. 1 second for a 16 MHz clock)
#define DELAY_1S 400000U

// ==== Function Prototypes ====
void delay(volatile uint32_t time);          // Simple delay function using a busy loop
void GPIO_Init(void);                        // Initializes GPIOA for PA0 (ADC) and PA2 (UART TX)
void USART2_Init(void);                      // Initializes USART2 peripheral
void ADC1_Init(void);                        // Initializes ADC1 for channel 0 (PA0)
uint16_t Read_ADC(void);                     // Reads raw ADC value from channel 0
void USART2_Write(char c);                   // Sends one character over UART
void USART2_Print(char *str);                // Sends a string over UART
float Read_Temperature(void);                // Converts ADC reading to temperature in °C

// ==== Delay Function ====
void delay(volatile uint32_t time) {
    while (time--);                          // Simple loop to introduce delay (not accurate)
}

// ==== GPIO Initialization ====
void GPIO_Init(void) {
    RCC->AHB1ENR |= RCC_AHB1ENR_GPIOAEN;     // Enable clock for GPIOA

    GPIOA->MODER |= (3 << 0);                // Set PA0 to analog mode (ADC input)

    GPIOA->MODER &= ~(3 << (2 * 2));         // Clear mode bits for PA2
    GPIOA->MODER |=  (2 << (2 * 2));         // Set PA2 to alternate function mode

    GPIOA->AFR[0] |= (7 << (4 * 2));         // Set alternate function for PA2 to AF7 (USART2_TX)
}

// ==== USART2 Initialization ====
void USART2_Init(void) {
    RCC->APB1ENR |= RCC_APB1ENR_USART2EN;    // Enable clock for USART2

    USART2->BRR = 0x0683;                    // Set baud rate to 9600 for 16 MHz system clock
    USART2->CR1 = USART_CR1_TE | USART_CR1_UE; // Enable transmitter and USART
}

// ==== Send a single character via UART ====
void USART2_Write(char c) {
    while (!(USART2->SR & USART_SR_TXE));    // Wait until transmit data register is empty
    USART2->DR = c;                          // Send the character
}

// ==== Send a string via UART ====
void USART2_Print(char *str) {
    while (*str) {
        USART2_Write(*str++);                // Send each character one by one
    }
}

// ==== ADC1 Initialization for channel 0 (PA0) ====
void ADC1_Init(void) {
    RCC->APB2ENR |= RCC_APB2ENR_ADC1EN;      // Enable clock for ADC1

    ADC1->SQR3 = 0;                          // Select channel 0 (PA0) for conversion
    ADC1->SMPR2 |= (7 << 0);                 // Set maximum sample time for accuracy
    ADC1->CR2 |= ADC_CR2_ADON;               // Turn on the ADC
}

// ==== Read value from ADC1 ====
uint16_t Read_ADC(void) {
    ADC1->CR2 |= ADC_CR2_SWSTART;            // Start conversion
    while (!(ADC1->SR & ADC_SR_EOC));        // Wait for conversion to complete
    return ADC1->DR;                         // Return converted value
}

// ==== Convert ADC value to Temperature in Celsius ====
float Read_Temperature(void) {
    uint16_t adc = Read_ADC();               // Read raw ADC value
    float voltage = (adc * 3.3f) / 4095.0f;   // Convert to voltage (assuming 3.3V reference)
    return voltage * 100.0f;                 // LM35 gives 10mV per °C → multiply by 100
}

// ==== Main Program Loop ====
int main(void) {
    char buffer[50];                         // Buffer to store formatted string
    float temp;                              // Variable to hold temperature value

    GPIO_Init();                             // Initialize GPIO for analog and UART
    USART2_Init();                           // Initialize UART for output
    ADC1_Init();                             // Initialize ADC for temperature sensor

    while (1) {
        temp = Read_Temperature();           // Read current temperature
        sprintf(buffer, "Temp: %.2f C\r\n", temp); // Format string with temperature
        USART2_Print(buffer);                // Send formatted string over UART
        delay(DELAY_1S);                     // Wait approx. 1 second
    }
}