🛠 Télémétrie série robuste vers le Traceur série

Objectives

Send data from the UNO to the PC properly: pace sampling with micros/millis instead of delay, save SRAM with the F macro, and above all, understand the DTR auto-reset quirk — the UNO resets every time the serial port is opened, and its bootloader "intercepts the first bytes" sent after connection.

Hardware

• 1 Arduino UNO R3 + USB-B cable (the 16U2 handles the USB-to-serial bridge, nothing else is required)
• PC with Arduino IDE (Serial Monitor + Serial Plotter)
• Optionally another serial terminal (PuTTY, screen) to reproduce the DTR quirk.

Complete Code

// Échantillonnage non bloquant 20 Hz sur A0, format Traceur série.
const uint32_t PERIODE_US = 50000;  // 50 ms = 20 Hz
uint32_t precedent = 0;

void setup {
  Serial.begin(115200);
  while (!Serial) { }   // attend l'ouverture du port (utile sur les cartes USB natives)
  Serial.println(F("pret"));  // F : la chaîne vit en flash, pas en SRAM (2 Ko seulement !)
}

void loop {
  uint32_t maintenant = micros;
  if (maintenant - precedent >= PERIODE_US) {
    precedent = maintenant;
    int a0 = analogRead(A0);
    int a1 = analogRead(A1);
    // Le Traceur série trace une courbe par valeur séparée par tabulation :
    Serial.print(a0); Serial.print("\t"); Serial.println(a1);
  }
  // ... ici on peut faire autre chose : le delay ne bloque plus la boucle.
}

Expected Verification

Tools > Serial Plotter: two continuous and regular curves, without gaps. If you open the Serial Monitor, the message "ready" appears (the board has just restarted — that's the DTR!). Test with a raw terminal: the first 2–3 characters emitted just after opening may be lost, and the first bytes YOU send may be swallowed by the bootloader.

Common Errors

• Believing that the first characters are lost "because of Arduino": it is the DTR reset + bootloader window, documented; on the PC side, open the port then wait ~2 s before sending data.
• Printing literals without F: with 2 KB of SRAM, a few Serial.print("long string") are enough to fragment memory and crash the board.
• delay between each measurement: the timing becomes inaccurate as soon as another task arrives; hence micros.
• Confusing Serial Monitor (text) and Serial Plotter (curves): without a tab between values, the Plotter displays only one curve.
• 9600 bauds for 20 Hz multi-channel data: switch to 115200, the 16U2 handles it without problem.