Here’s a clear introduction to the STM32 ADC principle, covering what it is, how it works inside the MCU, and what you need to know as a developer.

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1. What is an ADC?

• ADC = Analog-to-Digital Converter

• Converts a continuous analog signal (e.g., voltage from a sensor) into a digital value that the MCU can process.

• STM32 microcontrollers integrate successive approximation (SAR) ADCs, which balance speed and resolution.

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2. Key Features of STM32 ADC

• Resolution: Commonly 12-bit (0–4095), but some families allow 6, 8, 10, 12, 14, or even 16 bits.

• Input channels: Multiple (up to 16+), multiplexed into one ADC core.

• Reference voltage (Vref+): Defines full-scale range.

  • Input range: 0 V → Vref+ (e.g., 0–3.3 V).

• Sampling time: Adjustable — defines how long the ADC samples the input capacitor before conversion.

• Conversion speed: Up to several MSPS (mega-samples per second) depending on the STM32 family.

• Triggering: Can start conversions by software, timer events, or external pins.

• Modes:

  • Single conversion (one sample)

  • Continuous mode (keep sampling same channel)

  • Scan mode (sample multiple channels sequentially)

  • Injected mode (priority sampling, often synchronized with events like PWM edges)

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3. Principle of Operation

Inside STM32, the ADC works like this:

1. Sampling:

   • Input voltage is connected to a sample-and-hold capacitor.

   • Sampling time allows the capacitor to charge to the input level.

2. Quantization (SAR process):

   • Successive Approximation Register (SAR) compares the stored voltage against a reference (Vref) using a comparator + DAC.

   • Bit-by-bit, it decides if the input is above/below threshold, constructing a binary digital value.

3. Digital Output:

   • After conversion, the result (e.g., 0–4095 for 12-bit) is stored in the ADC Data Register (ADC_DR).

   • CPU, DMA, or peripherals can read the result.

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4. Example Conversion (12-bit, Vref = 3.3 V)

• Formula:

• If ADC result = 2048:

  Vin​=2048​/4095×3.3≈1.65V

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5. Practical Use in STM32

• Configure ADC in STM32CubeMX or register-level:

  • Enable ADC clock.

  • Select channel(s).

  • Configure resolution, sampling time, trigger source.

• Start conversion:

  • By software (HAL_ADC_Start()),

  • or automatically by timer trigger/DMA.

• Read result:

  • Polling (HAL_ADC_GetValue()),

  • Interrupt,

  • or via DMA (best for continuous multi-channel sampling).

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6. Applications

• Sensor interfacing (temperature, light, gas, etc.).

• Reading potentiometers / analog controls.

• Audio signal acquisition (low-to-mid speed).

• Power monitoring (voltage, current sensing).

• Motor control feedback (e.g., current shunt resistors).

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In summary:
The STM32 ADC is a SAR-based converter that samples analog voltages, compares them against a reference, and outputs a digital value. With multiple channels, flexible triggering, and DMA support, it’s powerful for real-time sensing tasks.