Dart开发：如何利用距离传感器触发函数？

Hey there! Awesome idea using a distance sensor to trigger functions with a hand wave in Dart—let’s walk through exactly how to pull this off, step by step.

First, you’ll need to match your setup to the device you’re using Dart on:

• Embedded devices (Raspberry Pi, ESP32):
  • Go for a cheap, easy-to-use sensor like the HC-SR04 (ultrasonic) or VL53L0X (laser for higher precision)
  • Use Dart libraries like dart_periphery (supports GPIO/I2C for Raspberry Pi) or esp32dart (built for ESP32) to interface with hardware
• Flutter mobile apps:
  • Phones don’t have distance sensors suitable for gesture detection, but you can either:
    • Use the camera + Google ML Kit for on-device gesture recognition, or
    • Connect a Bluetooth-enabled distance sensor and use flutter_blue_plus to read its data

A wave translates to quick, repeated distance changes: far → near → far (or a few cycles of this). Your code will need to:

• Continuously read distance values from the sensor
• Track recent readings to spot these rapid fluctuations
• Trigger your target function when the pattern matches a wave

Let’s put this into code with the dart_periphery library:

First, add the dependency to your pubspec.yaml:

dependencies:
  dart_periphery: ^1.4.0

Then the main code:

import 'dart:async';
import 'package:dart_periphery/dart_periphery.dart';

// Define sensor pins (adjust to your wiring)
const trigPin = 23;
const echoPin = 24;

// Store recent distances to detect patterns
List<double> recentDistances = [];
const maxRecentEntries = 3;

// Your target function to run when a wave is detected
void onWaveDetected() {
  print("Wave detected! Executing target function...");
  // Add your custom logic here
}

// Read distance from HC-SR04 (returns cm)
Future<double> readDistance() async {
  final gpioTrig = GPIO(trigPin, GPIOdirection.GPIO_OUT);
  final gpioEcho = GPIO(echoPin, GPIOdirection.GPIO_IN);

  // Send trigger signal
  await gpioTrig.write(0);
  await Future.delayed(Duration(microseconds: 2));
  await gpioTrig.write(1);
  await Future.delayed(Duration(microseconds: 10));
  await gpioTrig.write(0);

  // Measure echo duration
  while (await gpioEcho.read() == 0);
  final start = DateTime.now().microsecondsSinceEpoch;
  
  while (await gpioEcho.read() == 1);
  final end = DateTime.now().microsecondsSinceEpoch;

  // Calculate distance (speed of sound = 0.0343 cm/μs, divide by 2 for round trip)
  final distance = ((end - start) * 0.0343) / 2;

  gpioTrig.dispose();
  gpioEcho.dispose();

  return distance;
}

// Start monitoring for wave gestures
void startWaveDetection() {
  Timer.periodic(Duration(milliseconds: 100), (timer) async {
    final distance = await readDistance();
    // Filter out invalid readings (e.g., too far/close)
    if (distance < 10 || distance > 100) return;

    recentDistances.add(distance);
    if (recentDistances.length > maxRecentEntries) {
      recentDistances.removeAt(0);
    }

    // Check for wave pattern: middle reading is significantly closer than first/last
    if (recentDistances.length == maxRecentEntries) {
      final first = recentDistances[0];
      final middle = recentDistances[1];
      final last = recentDistances[2];

      if ((middle < first - 10) && (middle < last - 10)) {
        onWaveDetected();
        // Reset to avoid duplicate triggers
        recentDistances.clear();
      }
    }
  });
}

void main() async {
  print("Starting wave detection...");
  startWaveDetection();
  // Keep the program running
  await Future.delayed(Duration(days: 1));
}

• Calibrate sensitivity: Adjust the distance threshold (the 10 in the example) and sampling rate (100ms) to fit your space
• Filter noise: Smooth readings by taking averages of multiple samples to reduce false triggers
• Save power: If using a battery-powered device, lower the sampling frequency when idle
• Mobile alternative: For Flutter apps, use ML Kit’s gesture recognition to detect waves via the camera instead of a hardware sensor

内容的提问来源于stack exchange，提问作者Alex East