🛠 Entrées analogiques du Teensy 4.1 : 18 broches, 2 ADC, 0-3,3 V fixes et zéro DAC

Objectives

Master the Teensy 4.1 analog capabilities: 18 inputs distributed across 2 ADCs, default resolution of 10 bits, voltage range fixed at 0-3.3 V. Three documented disappointments to know before wiring: analogReference has no effect, the hardware 12-bit resolution is not practically usable ("only about 10 bits are usable due to noise," product page), and the board has no DAC — unlike the Teensy 3.5/3.6, analog audio output goes through I2S, the MQS pin, or a PT8211 kit. As compensation, 4 analog comparators are embedded.

Hardware

• 1 Teensy 4.1 + micro-USB data cable
• 1 10 kΩ potentiometer (3.3 V / A0 / GND) — never 5 V on the pin!
• Optional: a resistor and an LDR for a light-dependent voltage divider

Key Facts

• By default, analogRead returns 0..1023; the hardware range is exactly 0 to 3.3 V, with no selectable external reference.
• Analog pins do not tolerate 5 V: a voltage divider is mandatory upstream of a 5 V signal.
• There is no PGA or capacitive sensing embedded (absent from technical specs).
• EEPROM writes abruptly pause execution from flash: if you log analog measurements with EEPROM.update, expect micro-interruptions in timing.

Complete Code

const uint8_t AIN = 14; // A0 sur Teensy

void setup {
  Serial.begin(9600);
  while (!Serial && millis < 3000); // laisser monter l'USB série
  analogReadResolution(10);           // 10 bits : ce qui sert vraiment
}

void loop {
  long somme = 0;
  for (int i = 0; i < 64; i++) somme += analogRead(AIN);
  int moyenne = somme / 64;           // suréchantillonnage anti-bruit
  float volts = moyenne * 3.3f / 1023.0f;
  Serial.printf("A0 = %d  (%.3f V)\n", moyenne, volts);
  delay(250);
}

Expected Verification

When turning the potentiometer, the displayed voltage smoothly follows 0.000 → 3.300 V. Averaging over 64 samples stabilizes the last two digits: this is the counterpart to the noise floor documented by PJRC. To go further (precise triggering, hardware oversampling), Pedro Pereira's third-party ADC library is the community reference, but the 10 useful bits remain the physical ceiling.

Common Errors

• Calling analogReference(INTERNAL) or others: the function exists for Arduino compatibility but does nothing on the 4.1 — the range is hardware-fixed.
• Aiming for 4096 with analogReadResolution(12) and being surprised by noise: 12-bit resolution is there on paper, not in practice.
• Powering a sensor with 5 V and injecting its output directly: level shifting is mandatory.
• Comparing with a Teensy 3.6 looking for analogWrite DAC: the true 12-bit analog output is gone; for audio, see the Audio/I2S tutorial.