🛠 Faire clignoter la LED embarquée et lire la batterie

Objectives

Get started with the Arduino MKR GSM 1400 without using the cellular module: blink the onboard LED (pin D6, LED_BUILTIN) and read the LiPo battery voltage via the analog channel ADC_BATTERY (channel 32, 12-bit ADC). This tutorial validates the USB port, the SAM-BA bootloader, and the serial console before any GSM manipulation, where power supply issues are frequent.

Hardware

• Arduino MKR GSM 1400 board (ATSAMD21G18A, Cortex-M0+ 48 MHz)
• LiPo battery 3.7 V of at least 1500 mAh on the battery pads (Arduino declares it mandatory as soon as the radio module is used; here it is recommended to develop the right habit)
• Micro-USB data cable (not just a charging cable)
• Arduino IDE with the "Arduino SAMD Boards" core and the "Arduino MKR GSM 1400" board selected

Complete code

// LED embarquee D6 + lecture brute de la batterie (module GSM inutilise)
void setup {
  pinMode(LED_BUILTIN, OUTPUT);   // LED_BUILTIN = broche 6 (variant.h du core)
  Serial.begin(9600);             // Sur SAMD21, Serial == SerialUSB (CDC)
}

void loop {
  digitalWrite(LED_BUILTIN, !digitalRead(LED_BUILTIN));  // bascule a chaque tour
  int raw = analogRead(ADC_BATTERY);  // canal 32, ADC 12 bits
  Serial.print("VBAT raw: ");
  Serial.println(raw);
  delay(500);
}

Expected verification

After double-clicking the RST button and then uploading (using the bossac tool), the onboard LED blinks approximately every 500 ms and the USB console (9600 baud) displays a raw value that follows the battery charge. Without a battery, the reading changes or falls to a fixed value: this is normal, as the voltage sensor (ADC_BATTERY) depends on the actual board power supply.

Common errors

• Wrong board selected in the IDE: you must select "Arduino MKR GSM 1400", not "MKR WiFi 1010" or "Zero".
• Charging-only USB cable: the port never appears; try another cable and another port.
• Confusing the raw value with volts: the VBAT divider before the ADC is not reliably documented. >
• The Power LED remains on when running on battery: known and unresolved behavior (ArduinoCore-samd #515), not critical.
• Serial silent: is the board properly powered? Is the serial monitor opened AFTER the upload, on the correct port?