Bridge 02: Blink LED with Bridge

This is your first real Bridge project. Instead of the Arduino blinking on its own in a loop, Python is now in charge — it decides when to turn the LED on or off by sending a value (1 or 0) across the Bridge. The Arduino just listens and reacts.

This is the key shift: event-based control instead of a continuous loop.

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How It Works

1. Python calls a function on the Arduino side via the Bridge, passing 1 (ON) or 0 (OFF).
2. The Arduino receives that call and sets the LED state immediately.
3. The Arduino's loop() is intentionally empty — it does nothing on its own. It only acts when Python tells it to.

This pattern is the foundation of how the Python and Arduino sides cooperate in more complex Apps.

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The Code

main.py — Python side

from arduino.app_utils import *
import time

def loop():
    # 1. Turn it ON
    Bridge.call("control_led", 1)
    time.sleep(1)

    # 2. Turn it OFF
    Bridge.call("control_led", 0)
    time.sleep(1)

# Start the loop
App.run(user_loop=loop)

sketch.ino — Arduino side

#include <Arduino_RouterBridge.h>

// This function receives an integer (1 or 0) from Python
void control_led(int state) {

  // Clear if/else logic
  if (state == 1) {
    digitalWrite(LED_BUILTIN, LOW);  // Turn LED ON (Active Low)
  }
  else {
    digitalWrite(LED_BUILTIN, HIGH); // Turn LED OFF
  }

}

void setup() {
  pinMode(LED_BUILTIN, OUTPUT);
  Bridge.begin();
  Bridge.provide_safe("control_led", control_led);
}

void loop() {
  // Bridge runs automatically in the background
  // Arduino does nothing here — it only acts when Python calls it
}

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note

Event-based vs Continuous Loop Event-based vs Continuous Loop In a typical Arduino sketch, logic lives inside loop() and runs forever. Here, loop() is empty. The Arduino only reacts when Python sends a command via the Bridge. This makes the system more predictable and easier to reason about — Python is the "brain", Arduino is the "muscle".

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