🛠 ADC 12 bits et PWM sur la Nucleo-F401RE : oversampling, millivolts et LED en fondu

Goals

Use the two analog faces of the F401RE: the 12-bit ADC (16 channels) and timer-driven PWM via analogWrite. You will build a potentiometer-in, brightness-out loop with a proper millivolt conversion, then add oversampling to quiet the last digits.

Hardware

• 1× Nucleo-F401RE + micro-USB cable
• 10 kΩ potentiometer: outer legs to 3.3 V and GND, wiper to A0 (PA0)
• 1 LED + ~330 Ω resistor on D5 (any PWM-capable Arduino-header pin mapped by the core)

The facts

• The F401RE ADC is 12-bit (0–4095) over a 0–3.3 V range — scale millivolts with raw * 3300 / 4095.
• The core implements analogWrite on hardware timers ; no software bit-banging.
• >
• The chip also carries I2S and SDIO on-chip for real audio/SD streaming (see the advanced USB/SDIO tutorial).

Code

const int kFadePin  = D5;   // PWM-capable pin mapped by the core
const int kProbePin = A0;   // PA0 on the Arduino connector

void setup {
  Serial.begin(115200);     // ST-LINK VCP (USART2, PA2/PA3)
  analogWrite(kFadePin, 0);
}

void loop {
  // oversample: 64 reads averaged to stabilise the low digits
  long sum = 0;
  for (int i = 0; i < 64; i++) sum += analogRead(kProbePin);
  int raw = sum / 64;

  unsigned long mv = (unsigned long)(raw * 3300 / 4095);  // 12-bit scale
  int duty = map(raw, 0, 4095, 0, 255);
  analogWrite(kFadePin, duty);
  Serial.printf("raw=%4d  %4lu mV  duty=%3d\n", raw, mv, duty);
  delay(100);
}

Steps

1. Wire the potentiometer divider and the LED as described.
2. Upload with board Nucleo F401RE selected ; open the serial monitor at 115200.
3. Sweep the potentiometer: LED brightness and the mV column track together.
4. Compare a single analogRead against the 64-sample average — the flicker in the last digit disappears.

Expected result

A smooth 0 → 3300 mV sweep with a matching 0–255 PWM duty. The blink + fade + ADC-probe loop shipped in the core's own example set is the same pattern in one sketch: hard blink on PA5, software-visible PWM ramp with analogWrite, and a 12-bit probe printed over the ST-LINK VCP.

Common mistakes

• Scaling with 1023 (10-bit habit) — readings top out at a quarter of the range.
• Feeding a 5 V signal straight into A0: the MCU domain is 3.3 V (VDD 1.7–3.6 V) ; use a divider.
• Putting the LED directly on a GPIO without a series resistor.
• Searching for a DAC-grade analogWrite output: on this class of part, PWM + RC filter is the honest low-cost answer.