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Hedy
Hedy

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Using DMA-based ADC sampling with STM32 (HAL library)

#stm32 #stm32f103c8t6 #adcsampling #temperaturesensor

Here's an example of using DMA-based ADC sampling with STM32 (HAL library) to read analog temperature sensor data at regular intervals with minimal CPU load.

Goal:

  • Use ADC + DMA to sample analog voltage (e.g., from an NTC or LM35 sensor).
  • Use TIM3 to trigger ADC every 100ms.
  • Store data in a buffer.
  • Process temperature data later in your code (e.g., compute average).

Hardware Requirements:

STM32CubeMX Configuration:
1. Enable ADC1:

  • Mode: Scan Conversion Disabled
  • Continuous Conversion: Disabled
  • DMA Continuous Requests: Enabled
  • External Trigger: Timer 3 TRGO
  • Resolution: 12-bit

2. Enable DMA:

  • Circular Mode: Enabled
  • Direction: Peripheral to Memory

3. Configure Timer 3:

  • Set period to trigger ADC every 100 ms
  • TRGO event: Update Event

4. Configure PA0 as analog input

Auto-Generated HAL Code
In main.c:

Define ADC buffer:

c #define ADC_BUF_LEN 16 uint16_t adc_buffer[ADC_BUF_LEN];
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Start ADC + DMA:

c HAL_ADC_Start_DMA(&hadc1, (uint32_t*)adc_buffer, ADC_BUF_LEN);
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This begins continuous DMA transfer from ADC to memory.

Processing Data
In main.c inside the main loop:

c float read_temperature_from_adc(uint16_t raw) { float voltage = (raw / 4095.0f) * 3.3f; // Assuming Vref = 3.3V float temp_c = voltage * 100.0f; // For LM35: 10mV/°C return temp_c; } while (1) { HAL_Delay(1000); uint32_t sum = 0; for (int i = 0; i < ADC_BUF_LEN; i++) sum += adc_buffer[i]; uint16_t avg = sum / ADC_BUF_LEN; float temp = read_temperature_from_adc(avg); printf("Temperature: %.2f°C\r\n", temp); }
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Optional: Debug Output
Redirect printf() via UART or SWO for debugging.

Notes:

  • DMA in circular mode keeps filling the buffer without CPU intervention.
  • If needed, you can use DMA complete callback (HAL_ADC_ConvCpltCallback) to process each batch.
  • For multiple channels, enable scan mode and increase DMA buffer accordingly.

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