Add more or less working prototype

Signed-off-by: Severin Kaderli <severin@kaderli.dev>

src/MagSend/app/src/main/java/dev/kaderli/magsend/BaseActivity.kt

@@ -6,6 +6,9 @@ import androidx.appcompat.widget.Toolbar
 
 
 abstract class BaseActivity : AppCompatActivity() {
+  @Suppress("PropertyName")
+  protected val TAG: String = this::class.java.name
+
   override fun onCreate(savedInstanceState: Bundle?) {
     super.onCreate(savedInstanceState)
     setContentView(getLayoutId())

src/MagSend/app/src/main/java/dev/kaderli/magsend/BaseSensorActivity.kt

@@ -9,15 +9,23 @@ import android.os.Bundle
 import kotlin.math.pow
 import kotlin.math.sqrt
 
+const val SAMPLING_RATE = 0
+
+
 abstract class BaseSensorActivity : BaseActivity(), SensorEventListener {
   private lateinit var sensorManager: SensorManager;
   private lateinit var sensor: Sensor;
 
-  override fun onCreate(savedInstanceState: Bundle?) {
-    super.onCreate(savedInstanceState)
+  override fun onResume() {
+    super.onResume()
     sensorManager = getSystemService(Context.SENSOR_SERVICE) as SensorManager
     sensor = sensorManager.getDefaultSensor(Sensor.TYPE_MAGNETIC_FIELD);
-    sensorManager.registerListener(this, sensor, SensorManager.SENSOR_DELAY_UI);
+    sensorManager.registerListener(this, sensor, SAMPLING_RATE);
+  }
+
+  override fun onStop() {
+    super.onStop()
+    sensorManager.unregisterListener(this, sensor)
   }
 
   override fun onAccuracyChanged(sensor: Sensor?, accuracy: Int) {}

src/MagSend/app/src/main/java/dev/kaderli/magsend/ReceiveActivity.kt

@@ -1,7 +1,237 @@
 package dev.kaderli.magsend
 
-class ReceiveActivity : BaseActivity() {
+import android.os.Bundle
+import android.util.Log
+import android.view.View
+import android.widget.TextView
+import androidx.core.content.ContextCompat
+import dev.kaderli.magsend.model.Sample
+import dev.kaderli.magsend.model.Signal
+import java.lang.Integer.min
+
+const val NEEDED_SAMPLES_PER_SECOND = 190
+
+class ReceiveActivity : BaseSensorActivity() {
+  private lateinit var preambleStatus: TextView
+  private lateinit var headerStatus: TextView
+  private lateinit var receiveValue: TextView
+
+  /**
+   * List that contains all received samples from the sensor.
+   */
+  private var samples = ArrayList<Sample<Float>>()
+
+  /**
+   * A list that contains the samples as high or low signals.
+   */
+  private var signal = ArrayList<Sample<Signal>>()
+
+  private var preambleReceived = false
+
+  override fun onCreate(savedInstanceState: Bundle?) {
+    super.onCreate(savedInstanceState)
+    preambleStatus = findViewById(R.id.preambleStatus)
+    headerStatus = findViewById(R.id.headerStatus)
+    receiveValue = findViewById(R.id.receiveValue)
+  }
+
   override fun getLayoutId(): Int {
     return R.layout.activity_receive
   }
+
+  private fun getRangeOfData(): Float {
+    val maxValue = samples.maxByOrNull { it.value } ?: Sample(0f)
+    val minValue = samples.minByOrNull { it.value } ?: Sample(0f)
+    //Log.i(TAG, "Min: ${minValue}, Max: $maxValue")
+    return maxValue.value - minValue.value
+  }
+
+  private fun getThresholdForHighSignals(): Float {
+    if (getRangeOfData() < 3) {
+      return getMidRangeOfData() + 3
+    }
+
+    return getMidRangeOfData();
+  }
+
+  private fun getMidRangeOfData(): Float {
+    val maxValue = samples.maxByOrNull { it.value } ?: Sample(0f)
+    val minValue = samples.minByOrNull { it.value } ?: Sample(0f)
+    return (maxValue.value + minValue.value) / 2;
+  }
+
+  private fun isHigh(value: Float): Boolean {
+    return value > getThresholdForHighSignals()
+  }
+
+  private fun detectPreamble(): Boolean {
+    val cleanedSignal = cleanSignal(signal)
+    val compressedSignal = compressSignal(cleanedSignal)
+
+    if (compressedSignal.size < 4) {
+      return false
+    }
+
+    for (i in 0..compressedSignal.size - 4) {
+      val firstValue = compressedSignal[i]
+      val secondValue = compressedSignal[i + 1]
+      val thirdValue = compressedSignal[i + 2]
+      val fourthValue = compressedSignal[i + 3]
+
+      if (firstValue.value != Signal.High || secondValue.value != Signal.Low || thirdValue.value != Signal.High) {
+        continue
+      }
+
+      if (secondValue.timestamp - firstValue.timestamp > 2900 && thirdValue.timestamp - secondValue.timestamp > 2900 && fourthValue.timestamp - thirdValue.timestamp > 2900) {
+        return true
+      }
+    }
+
+    return false
+  }
+
+  private fun cleanSignal(signal: List<Sample<Signal>>): List<Sample<Signal>> {
+    // Remove outliers from the signal (single signal spikes or drops)
+    val cleanSignal = signal.filterIndexed { index, sample ->
+      var elementCount = 1
+
+      var previousIndex = index - 1
+      while (previousIndex > 0 && signal[previousIndex].value == sample.value) {
+        elementCount++
+        previousIndex--
+      }
+
+      var nextIndex = index + 1
+      while (nextIndex < signal.size && signal[nextIndex].value == sample.value) {
+        elementCount++
+        nextIndex++
+      }
+
+      elementCount > 5
+    }
+
+    return cleanSignal
+  }
+
+  private fun compressSignal(signal: List<Sample<Signal>>): List<Sample<Signal>> {
+    // Only keep the first of consecutive same signals
+    val compactSignal = ArrayList<Sample<Signal>>()
+    signal.forEach { sample ->
+      if (sample.value != compactSignal.lastOrNull()?.value) {
+        compactSignal.add(sample)
+      }
+    }
+
+    return compactSignal
+  }
+
+  private fun analyzePacketSignal(): List<Int> {
+    val cleanedSignal = cleanSignal(signal)
+    val compressedSignal = compressSignal(cleanedSignal)
+
+    if (compressedSignal.size < 2) {
+      return listOf()
+    }
+
+    val timeDifferences = ArrayList<Long>()
+    compressedSignal.forEachIndexed { index, sample ->
+      if (index == 0) {
+        return@forEachIndexed
+      }
+
+      timeDifferences.add(sample.timestamp - compressedSignal[index - 1].timestamp)
+    }
+
+    val clockTimeThreshold = 460//timeDifferences.max() * 0.75
+
+    val packetData = ArrayList<Int>()
+    compressedSignal.forEachIndexed { index, sample ->
+      if (index == 0) {
+        return@forEachIndexed
+      }
+
+      val timeDifference = sample.timestamp - compressedSignal[index - 1].timestamp
+      if (timeDifference > clockTimeThreshold && timeDifference < 2500) {
+        if (sample.value == Signal.High) {
+          packetData.add(0)
+        } else {
+          packetData.add(1)
+        }
+      }
+    }
+
+    //Log.i(TAG, "$timeDifferences")
+    //Log.i(TAG, "$cleanSignal")
+
+    return packetData
+  }
+
+  override fun sensorValueReceived(magneticFieldStrength: Float) {
+    // Add the current received sensor value to the samples
+    samples.add(Sample(magneticFieldStrength))
+
+    // Determine whether the sample is a high or low signal
+    val currentSignal: Sample<Signal> = if (isHigh(magneticFieldStrength)) {
+      Sample(Signal.High)
+    } else {
+      Sample(Signal.Low)
+    }
+    signal.add(currentSignal)
+
+    // Try to detect the preamble in the signal
+    if (!preambleReceived) {
+      if (detectPreamble()) {
+        preambleReceived = true
+        preambleStatus.setText(R.string.preamble_status_detected)
+        preambleStatus.setTextColor(ContextCompat.getColor(this, R.color.success))
+        signal.clear()
+        return
+      }
+    }
+
+    if (preambleReceived) {
+      val packet = analyzePacketSignal();
+
+      var payloadLength = 0
+      if (packet.size >= 4) {
+        payloadLength = listToInteger(packet.take(4))
+        headerStatus.text = getString(R.string.payload_length, payloadLength)
+      }
+
+      if (packet.size >= 4 + (8)) {
+        val numberOfAvailablePayloadBytes = min((packet.size - 4) / 8, payloadLength)
+        var payload = ""
+        for (i in 1..numberOfAvailablePayloadBytes) {
+          payload += listToInteger(packet.take(4 + (8 * i)).takeLast(8)).toChar().toString()
+        }
+
+        receiveValue.text = payload
+
+        if (packet.size >= 4 + (8 * payloadLength) + 8) {
+          // CRC Check
+          val crc = listToInteger(packet.take(4 + (8 * payloadLength) + 8).takeLast(8))
+          Log.i(TAG, "CRC: $crc")
+        }
+      }
+    }
+  }
+
+  private fun listToInteger(values: List<Int>): Int {
+    var value: Int = 0
+
+    for (bit in values) {
+      value = (value shl 1) + bit
+    }
+
+    return value
+  }
+
+
+  fun restartReceiveProcess(view: View) {
+    preambleReceived = false
+    preambleStatus.setText(R.string.preamble_status_not_detected)
+    preambleStatus.setTextColor(ContextCompat.getColor(this, R.color.error))
+    samples.clear()
+    signal.clear()
+  }
 }

src/MagSend/app/src/main/java/dev/kaderli/magsend/model/Sample.kt

@@ -0,0 +1,13 @@
+package dev.kaderli.magsend.model
+
+/**
+ * A simple data class that takes a value and stores it together with the
+ * current timestamp.
+ */
+data class Sample<T>(val value: T) {
+  val timestamp: Long = System.currentTimeMillis()
+
+  override fun toString(): String {
+    return value.toString()
+  }
+}

src/MagSend/app/src/main/java/dev/kaderli/magsend/model/Signal.kt

@@ -0,0 +1,9 @@
+package dev.kaderli.magsend.model
+
+/**
+ * A simple ENUM that is either low or high.
+ */
+enum class Signal {
+  Low,
+  High,
+}

src/MagSend/app/src/main/res/layout/activity_receive.xml

@@ -12,27 +12,51 @@
     android:id="@+id/receiveDescription"
     android:layout_width="wrap_content"
     android:layout_height="wrap_content"
+    android:paddingHorizontal="@dimen/layout_margins"
     android:text="@string/receive_description"
     app:layout_constraintEnd_toEndOf="parent"
     app:layout_constraintStart_toStartOf="parent"
     app:layout_constraintTop_toBottomOf="@+id/toolbar" />
 
+  <TextView
+    android:id="@+id/preambleStatus"
+    android:layout_width="0dp"
+    android:layout_height="wrap_content"
+    android:layout_marginTop="@dimen/component_spacing_small"
+    android:paddingHorizontal="@dimen/layout_margins"
+    android:text="@string/preamble_status_not_detected"
+    android:textColor="#FF0000"
+    app:layout_constraintEnd_toEndOf="parent"
+    app:layout_constraintStart_toStartOf="parent"
+    app:layout_constraintTop_toBottomOf="@+id/receiveDescription" />
+
+  <TextView
+    android:id="@+id/headerStatus"
+    android:layout_width="0dp"
+    android:layout_height="wrap_content"
+    android:layout_marginTop="@dimen/component_spacing_small"
+    android:paddingHorizontal="@dimen/layout_margins"
+    app:layout_constraintEnd_toEndOf="parent"
+    app:layout_constraintStart_toStartOf="parent"
+    app:layout_constraintTop_toBottomOf="@+id/preambleStatus" />
+
   <TextView
     android:id="@+id/receiveValue"
     android:layout_width="wrap_content"
     android:layout_height="wrap_content"
     android:layout_marginTop="@dimen/component_spacing"
-    android:text="82µT "
+    android:text="___"
     android:textSize="48sp"
     app:layout_constraintEnd_toEndOf="parent"
     app:layout_constraintStart_toStartOf="parent"
-    app:layout_constraintTop_toBottomOf="@+id/receiveDescription" />
+    app:layout_constraintTop_toBottomOf="@+id/headerStatus" />
 
   <TextView
     android:id="@+id/restartDescription"
     android:layout_width="wrap_content"
     android:layout_height="wrap_content"
     android:layout_marginTop="@dimen/component_spacing"
+    android:paddingHorizontal="@dimen/layout_margins"
     android:text="@string/restart_description"
     app:layout_constraintEnd_toEndOf="parent"
     app:layout_constraintStart_toStartOf="parent"
@@ -43,6 +67,7 @@
     android:layout_width="wrap_content"
     android:layout_height="wrap_content"
     android:layout_marginTop="8dp"
+    android:onClick="restartReceiveProcess"
     android:text="@string/restart_button_label"
     app:layout_constraintEnd_toEndOf="parent"
     app:layout_constraintStart_toStartOf="parent"

src/MagSend/app/src/main/res/values/colors.xml

@@ -7,4 +7,6 @@
     <color name="teal_700">#FF018786</color>
     <color name="black">#FF000000</color>
     <color name="white">#FFFFFFFF</color>
+    <color name="error">#FFFF0000</color>
+    <color name="success">#FF00FF00</color>
 </resources>

src/MagSend/app/src/main/res/values/dimens.xml

@@ -3,4 +3,5 @@
   <dimen name="layout_margins">16dp</dimen>
   <dimen name="component_spacing">24dp</dimen>
   <dimen name="title_text_size">48sp</dimen>
+    <dimen name="component_spacing_small">8dp</dimen>
 </resources>

src/MagSend/app/src/main/res/values/strings.xml

@@ -11,4 +11,7 @@
   <string name="calibration_activity_label">Calibration</string>
   <string name="receive_activity_label">Receive</string>
   <string name="calibration_value">%1$.2f µT</string>
+  <string name="preamble_status_not_detected">Preamble not detected X</string>
+  <string name="preamble_status_detected">Preamble detected ✓</string>
+  <string name="payload_length">The payload length is %1$d bytes</string>
 </resources>

src/website/scripts/Constants.js

@@ -1,10 +1,19 @@
 class Constants {
   /**
-   * The amount of time in ms a bit takes to transmit.
+   * The amount of time in ms a symbol takes to transmit.
    *
    * @type {Number}
    */
   static get CLOCK_TIME() {
+    return 500;
+  }
+
+  /**
+   * The amount of time in ms a symbol of the preamble takes to transmit.
+   *
+   * @type {Number}
+   */
+  static get PREAMBLE_CLOCK_TIME() {
     return 1000;
   }
 

src/website/scripts/Main.js

@@ -81,7 +81,7 @@ async function startCalibration() {
         return;
       }
 
-      await transmitBit(Constants.CALIBRATION_SIGNAL[i]);
+      await transmitBit(Constants.CALIBRATION_SIGNAL[i], Constants.CLOCK_TIME);
     }
   }
 }
@@ -124,6 +124,7 @@ function startSending() {
   stopSendingButton.classList.remove(Constants.HIDE_CLASS);
 
   const packet = new Packet(textInput.value);
+  console.log(packet);
   const signal = Utility.manchesterEncode(packet.getData());
 
   isTransmitting = true;
@@ -158,7 +159,7 @@ async function transmitSignal(signal) {
       }
 
       console.log(`Sending preamble: ${bit}`);
-      await transmitBit(bit);
+      await transmitBit(bit, Constants.PREAMBLE_CLOCK_TIME);
     }
 
     for (let i = 0; i < signal.length; i++) {
@@ -167,24 +168,24 @@ async function transmitSignal(signal) {
         return;
       }
 
-      console.log(`Sending bit ${i + 1} of ${signal.length} of packet: ${signal[i]}`);
-      await transmitBit(signal[i]);
+      console.log(`Sending symbol ${i + 1} of ${signal.length} of packet: ${signal[i]}`);
+      await transmitBit(signal[i], Constants.CLOCK_TIME);
     }
   }
 }
 
 /**
  * Starts or stops the web workers depending on the bit value and then waits
- * for a duration of Constants.CLOCK_TIME.
+ * for a duration of clockTime.
  *
  * @param {Number} bit
  */
-function transmitBit(bit) {
+function transmitBit(bit, clockTime) {
   if (bit === 1) {
     startWorkers();
-    return new Promise((resolve) => setTimeout(resolve, Constants.CLOCK_TIME));
+    return new Promise((resolve) => setTimeout(resolve, clockTime));
   }
 
   stopWorkers();
-  return new Promise((resolve) => setTimeout(resolve, Constants.CLOCK_TIME));
+  return new Promise((resolve) => setTimeout(resolve, clockTime));
 }

src/website/scripts/Utility.js

@@ -56,8 +56,8 @@ class Utility {
     const encodedBits = [];
 
     for (const bit of bitArray) {
-      encodedBits.push(bit ^ 1);
       encodedBits.push(bit ^ 0);
+      encodedBits.push(bit ^ 1);
     }
 
     return encodedBits;