🛠 Générer une vraie tension analogique avec les DAC 12 bits (broches 66 et 67)

Objectives

Use what almost no other classic Arduino has: TWO true 12-bit analog outputs (the DACC peripheral), on pins DAC0 = digital pin 66 and DAC1 = pin 67. No more PWM that needs filtering: here the output voltage directly follows the written value, between 0 and 3.3 V. You will generate a ramp and then a sine wave, and uncover the issue with the default resolution (8 bits when writing!).

Hardware

• 1 Arduino Due
• 1 oscilloscope (or a multimeter for the slow version) + ground probe
• Micro-USB cable
• Headphones/piezo possible in a variant (via a 1 µF coupling capacitor)

Complete code

// Rampe + sinusoïde sur DAC0 (broche 66) — DACC 12 bits
#include <math.h>

const uint8_t DAC0_PIN = DAC0;   // 66 (PB15). DAC1 = 67 (PB16)

void setup {
  analogWriteResolution(12);     // sans ça : écritures 8 bits (0..255) par défaut !
  SerialUSB.begin(115200);
}

void loop {
  // 1) Rampe en dents de scie 0..4095
  for (int v = 0; v <= 4095; v += 32) {
    analogWrite(DAC0_PIN, v);
    delay(2);
  }
  // 2) Sinusoïde centrée 0..4095 autour de 1,65 V
  for (int i = 0; i < 64; i++) {
    float t = i * 2.0f * PI / 64.0f;
    int v = 2048 + (int)(2000.0f * sinf(t));
    analogWrite(DAC0_PIN, v);
    delay(2);
  }
  SerialUSB.println("cycle DAC0 terminé");
}

Expected verification

On the oscilloscope (DC coupling, time base ~50 ms/div), pin 66 shows a true continuous ramp — not PWM square waves — rising from 0 to ~3.3 V, then a sine wave sampled in steps of 32/4096 ≈ 25 mV. With a multimeter in DC mode, a fixed written value (e.g., 2048) gives ~1.65 V immediately, without an RC filter.

Common errors

• Forgetting analogWriteResolution(12): the core writes in 8 bits by default, your values 0–4095 are clipped to 255 and the voltage caps at ~2/3 of the range… without any error message.
• Looking for the DAC on PWM pins 2–13: PWM (12 pins, 8 bits / 1 kHz by default) is NOT the DAC; the only true analog outputs are 66 and 67.
• Measuring with a poorly placed oscilloscope ground and concluding the signal is noisy: place the GND clip as close as possible to DAC0.
• Expecting current: the DACC drives logic, not a loudspeaker; add an operational amplifier or a power transistor for any actuator.
• Confusing DAC0 (66) with a Mega-format digital pin: on a Due, pin 66 is real, but on a shield designed for Mega it is occupied — check the pinout before stacking.
• Outputting out of range: the output never exceeds 0–3.3 V, any 5 V expectation on the receiving side requires an amplifier.