🛠 Télémétrie : pousser une mesure du capteur vers le réseau

Objectives

Chain the two worlds together for a first data pipeline: the SAMD21 acquires the measurement (12-bit ADC on A0), transmits it to the Bridge, and the Linux side sends it over the network via HTTP. You will discover the "MCU measures, Linux transports" pattern — the raison d'être of the Tian compared to a microcontroller-only board.

Hardware

• 1 Arduino Tian connected to the network (see the web panel/SSH tutorial)
• 1 LDR + 10 kΩ in a voltage divider on A0 (midpoint to A0)
• A test PC running a mini HTTP server listening for POST requests, for example:

# sur le PC, pour recevoir : nc -l -p 8080   (netcat) ou tout serveur web local

Complete code

// Le SAMD21 mesure, Linux expédie.
#include <Bridge.h>

const uint8_t LDR = A0;
const uint32_t PERIODE = 10000;   // 1 POST toutes les 10 s
uint32_t precedent = 0;

void setup {
  Serial.begin(9600);
  while (!Serial) { }
  Bridge.begin;
}

void loop {
  uint32_t maintenant = millis;
  if (maintenant - precedent < PERIODE) return;
  precedent = maintenant;

  int v = analogRead(LDR);        // 0..4095 (ADC 12 bits)
  String cmd = "curl -s -m 5 -X POST -d ldr=" + String(v);
  cmd += " http://192.168.1.20:8080/tian";   // IP de votre PC
  BridgeProcess p = Bridge.runShellCommand(cmd);
  p.readString;                  // vide la sortie, évite les blocages
  Serial.print(F("envoye ldr=")); Serial.println(v);
}

Expected verification

On the PC side, each received POST displays "ldr=xxxx" which follows your light variations (cover the LDR, the value drops). Cut the router's WiFi: transmissions fail but the sketch continues to measure — robustness comes from curl's timeout -m 5, which prevents the loop from blocking.

Common errors

• curl missing from the base Linino image: opkg update && opkg install curl ca-bundle via SSH; otherwise use busybox wget as a fallback.
• Hardcoding the IP everywhere: centralize the configuration, otherwise every DHCP change costs you an hour.
• POSTing on every loop iteration: the Bridge is not a real-time bus, throttle it (10 s here); Linux logs everything.
• >
• Comparing millis with < instead of unsigned subtraction: overflow (~49 days) freezes the cadence.
• Embedding data in the shell command without escaping: a sensor name with spaces breaks the command line — hence a simple numeric payload here.