feat: Add support for SHT21 sensor

lib/communication/sensors/sht21.dart

@@ -0,0 +1,57 @@
+import 'dart:async';
+import '../peripherals/i2c.dart';
+
+class SHT21 {
+  // SHT21 Default I2C Address
+  static const int addr = 0x40;
+
+  // The I2C helper instance (passed in from the main app)
+  final I2C i2c;
+
+  // Constructor: Ask for the I2C object instead of trying to create a new empty one
+  SHT21(this.i2c);
+
+  // Commands (No Hold Master Mode)
+  static const int _triggerTempMeasure = 0xF3;
+  static const int _triggerHumMeasure = 0xF5;
+
+  /// Read Temperature in Celsius
+  Future<double> getTemperature() async {
+    // 1. Send the "Measure" command
+    // We use writeBulk because it sends the bytes directly to the address
+    await i2c.writeBulk(addr, [_triggerTempMeasure]);
+
+    // 2. Wait for measurement (Datasheet max ~85ms)
+    await Future.delayed(Duration(milliseconds: 100));
+
+    // 3. Read 3 bytes (MSB, LSB, Checksum)
+    // simpleRead automatically handles the "Start Condition" + "Read" logic
+    List<int> data = await i2c.simpleRead(addr, 3);
+
+    if (data.length < 2) return 0.0;
+
+    // 4. Combine bytes & clear status bits
+    int rawValue = (data[0] << 8) | (data[1] & 0xFC);
+
+    // 5. Calculate Formula
+    return -46.85 + 175.72 * (rawValue / 65536.0);
+  }
+
+  /// Read Humidity in %RH
+  Future<double> getHumidity() async {
+    // 1. Send Measure Command
+    await i2c.writeBulk(addr, [_triggerHumMeasure]);
+
+    // 2. Wait
+    await Future.delayed(Duration(milliseconds: 100));
+
+    // 3. Read
+    List<int> data = await i2c.simpleRead(addr, 3);
+    if (data.length < 2) return 0.0;
+
+    int rawValue = (data[0] << 8) | (data[1] & 0xFC);
+
+    // 4. Calculate
+    return -6.0 + 125.0 * (rawValue / 65536.0);
+  }
+}

lib/main.dart

@@ -1,3 +1,4 @@
+import 'package:pslab/providers/sht21_provider.dart';
 import 'package:flutter/material.dart';
 import 'package:flutter_screenutil/flutter_screenutil.dart';
 import 'package:provider/provider.dart';
@@ -42,6 +43,11 @@ void main() {
         ChangeNotifierProvider<BoardStateProvider>(
           create: (context) => getIt<BoardStateProvider>(),
         ),
+        // --- ADD THIS BLOCK BELOW ---
+        ChangeNotifierProvider<SHT21Provider>(
+          create: (context) => SHT21Provider(),
+        ),
+        // ----------------------------
       ],
       child: const MyApp(),
     ),

lib/providers/sht21_provider.dart

@@ -0,0 +1,43 @@
+import 'dart:async';
+import 'package:flutter/foundation.dart';
+import '../communication/sensors/sht21.dart';
+import '../communication/peripherals/i2c.dart';
+
+class SHT21Provider with ChangeNotifier {
+  SHT21? _sensor;
+  bool isWorking = false;
+  double temp = 0.0;
+  double hum = 0.0;
+
+  // Initialize the sensor with the I2C connection
+  Future<void> init(I2C i2c) async {
+    // This fixes the lint warning you saw earlier
+    _sensor ??= SHT21(i2c);
+  }
+
+  // Start the loop to read data
+  Future<void> startDataLog() async {
+    if (_sensor == null) return;
+
+    isWorking = true;
+    notifyListeners();
+
+    while (isWorking) {
+      // Fetch new values
+      temp = await _sensor!.getTemperature();
+      hum = await _sensor!.getHumidity();
+
+      // Update UI
+      notifyListeners();
+
+      // Wait 1 second before next read
+      await Future.delayed(Duration(milliseconds: 1000));
+    }
+  }
+
+  // Stop the loop
+  void stopDataLog() {
+    isWorking = false;
+    notifyListeners();
+  }
+}

lib/view/sensors_screen.dart

@@ -1,3 +1,4 @@
+import 'package:pslab/view/sht21_screen.dart';
 import 'package:flutter/material.dart';
 import 'package:provider/provider.dart';
 import 'package:pslab/view/bmp180_screen.dart';
@@ -229,9 +230,13 @@ class _SensorsScreenState extends State<SensorsScreen> {
         break;
       case 'APDS9960':
         targetScreen = const APDS9960Screen();
+        break;
       case 'VL53L0X':
         targetScreen = const VL53L0XScreen();
         break;
+      case 'SHT21':
+        targetScreen = const SHT21Screen();
+        break;
       default:
         ScaffoldMessenger.of(context).showSnackBar(
           SnackBar(

lib/view/sht21_screen.dart

@@ -0,0 +1,122 @@
+import 'package:flutter/material.dart';
+import 'package:provider/provider.dart';
+import 'package:pslab/communication/science_lab.dart';
+import 'package:pslab/communication/peripherals/i2c.dart'; // Import I2C class
+import 'package:pslab/providers/locator.dart';
+import '../providers/sht21_provider.dart';
+
+class SHT21Screen extends StatefulWidget {
+  const SHT21Screen({super.key});
+
+  @override
+  State<SHT21Screen> createState() => _SHT21ScreenState();
+}
+
+class _SHT21ScreenState extends State<SHT21Screen> {
+  @override
+  void initState() {
+    super.initState();
+    WidgetsBinding.instance.addPostFrameCallback((_) {
+      final sht21Provider = Provider.of<SHT21Provider>(context, listen: false);
+
+      // 1. Get the ScienceLab instance
+      final scienceLab = getIt<ScienceLab>();
+
+      // 2. Check connection
+      if (scienceLab.isConnected()) {
+        // 3. MANUALLY create the I2C helper using the packet handler
+        // This fixes the "getter i2c not defined" error
+        I2C i2c = I2C(scienceLab.mPacketHandler);
+
+        // 4. Initialize the sensor provider
+        sht21Provider.init(i2c);
+        sht21Provider.startDataLog();
+      } else {
+        ScaffoldMessenger.of(context).showSnackBar(
+          const SnackBar(content: Text('Device not connected')),
+        );
+      }
+    });
+  }
+
+  @override
+  void dispose() {
+    // Stop the data loop when leaving the screen
+    if (mounted) {
+      Provider.of<SHT21Provider>(context, listen: false).stopDataLog();
+    }
+    super.dispose();
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    return Scaffold(
+      appBar: AppBar(
+        title: const Text('SHT21 Sensor'),
+      ),
+      body: Consumer<SHT21Provider>(
+        builder: (context, provider, child) {
+          return Padding(
+            padding: const EdgeInsets.all(16.0),
+            child: Column(
+              children: [
+                _buildSensorCard(
+                  title: "Temperature",
+                  value: provider.temp.toStringAsFixed(2),
+                  unit: "°C",
+                  icon: Icons.thermostat,
+                  color: Colors.redAccent,
+                ),
+                const SizedBox(height: 20),
+                _buildSensorCard(
+                  title: "Humidity",
+                  value: provider.hum.toStringAsFixed(2),
+                  unit: "%",
+                  icon: Icons.water_drop,
+                  color: Colors.blueAccent,
+                ),
+              ],
+            ),
+          );
+        },
+      ),
+    );
+  }
+
+  Widget _buildSensorCard({
+    required String title,
+    required String value,
+    required String unit,
+    required IconData icon,
+    required Color color,
+  }) {
+    return Card(
+      elevation: 4,
+      child: Padding(
+        padding: const EdgeInsets.all(20.0),
+        child: Row(
+          children: [
+            Icon(icon, size: 40, color: color),
+            const SizedBox(width: 20),
+            Column(
+              crossAxisAlignment: CrossAxisAlignment.start,
+              children: [
+                Text(title,
+                    style: const TextStyle(fontSize: 18, color: Colors.grey)),
+                Row(
+                  children: [
+                    Text(value,
+                        style: const TextStyle(
+                            fontSize: 32, fontWeight: FontWeight.bold)),
+                    const SizedBox(width: 5),
+                    Text(unit, style: const TextStyle(fontSize: 20)),
+                  ],
+                ),
+              ],
+            ),
+          ],
+        ),
+      ),
+    );
+  }
+}