This code implements a STM32 microcontroller application where an ADC...

August 31, 2025 at 08:22 PM

#include "main.h"
 
uint32_t AD_RES_BUFFER[4];
ADC_HandleTypeDef hadc1;
DMA_HandleTypeDef hdma_adc1;
TIM_HandleTypeDef htim2;
 
void SystemClock_Config(void);
static void MX_GPIO_Init(void);
static void MX_DMA_Init(void);
static void MX_ADC1_Init(void);
static void MX_TIM2_Init(void);
 
int main(void)
{
    HAL_Init();
    SystemClock_Config();
    MX_GPIO_Init();
    MX_DMA_Init();
    MX_ADC1_Init();
    MX_TIM2_Init();
    HAL_TIM_PWM_Start(&htim2, TIM_CHANNEL_1);
    HAL_TIM_PWM_Start(&htim2, TIM_CHANNEL_2);
    HAL_TIM_PWM_Start(&htim2, TIM_CHANNEL_3);
    HAL_TIM_PWM_Start(&htim2, TIM_CHANNEL_4);
 
    while (1)
    {
        // Start ADC Conversion in DMA Mode (Periodically Every 1ms)
        HAL_ADC_Start_DMA(&hadc1, AD_RES_BUFFER, 4);
        HAL_Delay(1);
    }
}
 
void HAL_ADC_ConvCpltCallback(ADC_HandleTypeDef* hadc)
{
    // Conversion Complete & DMA Transfer Complete As Well
    // So The AD_RES_BUFFER Is Now Updated & Let's Move Values To The PWM CCRx
    // Update The PWM Channels With Latest ADC Scan Conversion Results
    TIM2->CCR1 = (AD_RES_BUFFER[0] << 4);  // ADC CH6 -> PWM CH1
    TIM2->CCR2 = (AD_RES_BUFFER[1] << 4);  // ADC CH7 -> PWM CH2
    TIM2->CCR3 = (AD_RES_BUFFER[2] << 4);  // ADC CH8 -> PWM CH3
    TIM2->CCR4 = (AD_RES_BUFFER[3] << 4);  // ADC CH9 -> PWM CH4
}

This code implements a STM32 microcontroller application where an ADC (Analog-to-Digital Converter) is used to measure input signals, transfer the conversion results via DMA (Direct Memory Access), and update the duty cycle of four PWM (Pulse Width Modulation) channels in a timer. Here's a breakdown of what the code does:

1. Initialization:

The code initializes various hardware components:

HAL_Init(): Initializes the STM32 HAL (Hardware Abstraction Layer) library.
SystemClock_Config(): Configures the system clock for the STM32 microcontroller.
MX_GPIO_Init(), MX_DMA_Init(), MX_ADC1_Init(), MX_TIM2_Init(): Initialize GPIO pins, DMA, the ADC peripheral, and Timer 2 (TIM2) for PWM generation.

2. PWM Generation:

The following lines:

HAL_TIM_PWM_Start(&htim2, TIM_CHANNEL_X);

start PWM output on all four channels (CH1, CH2, CH3, CH4) of Timer 2. PWM is a technique where the duty cycle of a square wave can be varied to control analog-like outputs (e.g., LED brightness or motor speed). At this point, the initial PWM duty cycles could already be configured.

3. ADC Conversion with DMA:

Inside the infinite loop in the main() function:

HAL_ADC_Start_DMA(&hadc1, AD_RES_BUFFER, 4);

starts an ADC conversion in DMA mode. The results of the ADC conversion will be stored in the AD_RES_BUFFER, a buffer array of 4 elements corresponding to 4 analog input channels being sampled.

The use of DMA ensures efficient data transfer from the ADC peripheral to the memory buffer without involving the CPU.

The HAL_Delay(1) introduces a 1-millisecond delay between consecutive ADC starts.

4. Handling ADC Conversion Complete:

The HAL_ADC_ConvCpltCallback() function is called by the HAL when an ADC conversion and corresponding DMA transfer are complete. The callback performs the following steps:

Updates the duty cycle of the four PWM channels based on the values stored in AD_RES_BUFFER. For example:
```
TIM2->CCR1 = (AD_RES_BUFFER[0] << 4);
```
This sets the Capture/Compare Register (CCR) of Timer 2 Channel 1 (TIM2->CCR1). The captured ADC value (e.g., AD_RES_BUFFER[0]) is left-shifted by 4 bits to scale it, and this value determines the duty cycle of the PWM waveform for that channel.

Each index in the AD_RES_BUFFER array corresponds to a specific ADC channel:

AD_RES_BUFFER[0]: ADC Channel 6 → PWM Channel 1
AD_RES_BUFFER[1]: ADC Channel 7 → PWM Channel 2
AD_RES_BUFFER[2]: ADC Channel 8 → PWM Channel 3
AD_RES_BUFFER[3]: ADC Channel 9 → PWM Channel 4

5. Effect of the Code:

In summary:

The ADC continuously samples four analog channels at regular intervals (1ms).
The DMA transfers ADC results to the AD_RES_BUFFER without CPU intervention.
When the ADC results are ready, the HAL_ADC_ConvCpltCallback function updates the PWM duty cycles of four timer channels based on the sampled values.
The PWM output (e.g., LED brightness, motor speed) is dynamically adjusted in real time according to the analog input signals.

This is a common implementation for applications requiring real-time control, such as motor control, proportional valve control, or LED dimming.

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