Improve reading stability and implement an abort option

Author: GatCode

README.md

@@ -15,6 +15,10 @@ Since the usage of load cells for accurate weight measurement is always correlat
 
 This library provides an easy way to accommodate for these errors without sacrificing measurement speed or the implementation of accurate timing measurements.
 
+Below you can see an example how the ScaleStabilizer can improve the reading stability in a real-world project.
+
+![](assets/ScaleStabilizer.gif)
+
 The idea for the two basic algorithms behind this library were borrowed from *Colm Slattery* *and Mariah Nie's* [A Reference Design for High-Performance, Low-Cost Weigh Scales | Analog Devices](https://www.analog.com/en/analog-dialogue/articles/a-reference-design-for-weigh-scales.html), which describes an excellent way to solve these problems.
 
 ## Basic principle
@@ -41,8 +45,8 @@ const int SCK_PIN = 22;
 HX711 scale;
 
 // Scale Stabilizer
-const int WINDOW_SIZE = 10;
-const double WEIGHT_THRESHOLD = 0.01;
+const int WINDOW_SIZE = 12;
+const double WEIGHT_THRESHOLD = 0.05;
 ScaleStabilizer stabilizer;
 
 void setup() {

assets/ScaleStabilizer.gif

@@ -7,8 +7,8 @@ const int SCK_PIN = 22;
 HX711 scale;
 
 // Scale Stabilizer
-const int WINDOW_SIZE = 10;
-const double WEIGHT_THRESHOLD = 0.01;
+const int WINDOW_SIZE = 12;
+const double WEIGHT_THRESHOLD = 0.05;
 ScaleStabilizer stabilizer;
 
 void setup() {
@@ -25,4 +25,4 @@ void loop() {
   double adcReading = scale.get_units();
   stabilizer.add(adcReading);
   Serial.println(stabilizer.getStablilizedReading());
-}
+}

examples/basic/basic.ino

@@ -1,6 +1,6 @@
 {
   "name": "ScaleStabilizer",
-  "version": "1.0.2",
+  "version": "1.1.0",
   "description": "A library to stabilize load cell readings",
   "keywords": "scale, load cell, HC711",
   "repository":

library.json

@@ -1,5 +1,5 @@
 name=ScaleStabilizer
-version=1.0.2
+version=1.1.0
 author=GatCode <gatcode@wdw.one>
 maintainer=GatCode <gatcode@wdw.one>
 sentence=A library to stabilize load cell readings.

library.properties

@@ -14,33 +14,41 @@ ScaleStabilizer::~ScaleStabilizer()
 }
 
 /*!
- * @brief simple average calculation
+ * @brief M-2 average calculation
  */
 double ScaleStabilizer::getAvg()
 {
-  double sum = 0;
-
+  // find min and max values
+  int minIdx = 0;
+  double minReading = _window[minIdx];
+  int maxIdx = 0;
+  double maxReading = _window[maxIdx];
   for (int i = 0; i < _windowSize; i++)
   {
-    sum += _window[i];
+    if (_window[i] < minReading)
+    {
+      minIdx = i;
+      minReading = _window[i];
+    }
+    if (_window[i] > maxReading)
+    {
+      maxIdx = i;
+      maxReading = _window[i];
+    }
   }
 
-  return sum / _windowSize;
-}
-
-/*!
- * @brief checks if all the elements in the moving _window are the same
- */
-bool ScaleStabilizer::isBufferMonotone()
-{
+  // remove min and max from measurements
+  double sum = 0;
   for (int i = 0; i < _windowSize; i++)
   {
-    if (_window[i] != _window[0])
+    if (i == minIdx || i == maxIdx)
     {
-      return false;
+      continue;
     }
+    sum += _window[i];
   }
-  return true;
+
+  return sum / (_windowSize - 2);
 }
 
 /*!
@@ -54,6 +62,12 @@ void ScaleStabilizer::begin(int windowSize, double weightThreshold)
   _forceOverwrite = _windowSize;
   _currentReadingIdx = 0;
   _lastOutputValue = 0.0;
+  _abortCounter = _windowSize / 2;
+
+  for (int i = 0; i < _windowSize; i++)
+  {
+    _window[i] = 0.0;
+  }
 }
 
 /*!
@@ -62,7 +76,7 @@ void ScaleStabilizer::begin(int windowSize, double weightThreshold)
  */
 void ScaleStabilizer::add(double reading)
 {
-  if (_forceOverwrite > 0 || isBufferMonotone())
+  if (_forceOverwrite > 0)
   {
     int oldestReadingIdx = (_currentReadingIdx + 1) % _windowSize;
     _window[oldestReadingIdx] = reading;
@@ -76,6 +90,7 @@ void ScaleStabilizer::add(double reading)
     int oldestReadingIdx = (_currentReadingIdx + 1) % _windowSize;
     _window[oldestReadingIdx] = reading;
     _currentReadingIdx = oldestReadingIdx;
+    _abortCounter = _abortCounter < _windowSize / 2 ? _abortCounter++ : _abortCounter;
     return;
   }
 
@@ -84,68 +99,50 @@ void ScaleStabilizer::add(double reading)
 
   if (abs(_window[nextToLastReadingIdx] - getAvg()) > _weightThreshold)
   {
-    // replace 75% of the data in the filter _window with fresh readings
-    _forceOverwrite = _windowSize * 0.75;
+    // replace all the data in the filter _window with fresh readings for the next six cycles
+    _forceOverwrite = _windowSize * 6;
+    return;
   }
 
-  // everything else is probably just noise
+  // everything else is probably just noise but abort if stuck
+  if (_abortCounter <= 0)
+  {
+    _forceOverwrite = _windowSize;
+    _abortCounter = _windowSize / 2;
+  }
+  _abortCounter--;
 }
 
 /*!
  * @brief returns the stabilized average reading from the moving _window
  */
 double ScaleStabilizer::getStablilizedReading(double displayResolution, int decimalPlaces)
 {
-  // find min and max values
-  int minIdx = 0;
-  int maxIdx = 0;
-  for (int i = 0; i < _windowSize; i++)
-  {
-    if (_window[i] < minIdx)
-    {
-      minIdx = i;
-    }
-    if (_window[i] > maxIdx)
-    {
-      maxIdx = i;
-    }
-  }
-
-  // remove min and max from measurements
-  double sum = 0;
-  for (int i = 0; i < _windowSize; i++)
-  {
-    if (i == minIdx || i == maxIdx)
-    {
-      continue;
-    }
-    sum += _window[i];
-  }
-
-  // calc cleaned average
-  double cleanedAverage = sum / (_windowSize - 2);
+  double codeValue = getAvg();
+  double outputValue = codeValue;
 
   // remove negative numbers and set to 0 if close to 0
-  if (cleanedAverage < 0.5)
+  if (outputValue < 0.5)
   {
-    cleanedAverage = 0.0;
+    outputValue = 0.0;
   }
 
   // round to given decimal places
   float scale = pow(10, decimalPlaces);
-  cleanedAverage = round(cleanedAverage * scale) / scale;
+  outputValue = round(outputValue * scale) / scale;
 
   // perform the output flicker reduction
-  if (_lastOutputValue == cleanedAverage)
+  if (_lastOutputValue == outputValue)
   {
-    return cleanedAverage;
+    _lastCodeValue = codeValue;
+    return _lastOutputValue;
   }
 
-  if (abs(cleanedAverage - _lastOutputValue) < displayResolution)
+  if (abs(codeValue - _lastCodeValue) > displayResolution)
   {
-    return _lastOutputValue; // probably was just noise - return the old measurement
+    _lastCodeValue = codeValue;
+    _lastOutputValue = outputValue;
   }
 
-  _lastOutputValue = cleanedAverage;
-  return cleanedAverage;
+  return _lastOutputValue;
 }

src/ScaleStabilizer.cpp

@@ -12,19 +12,15 @@ class ScaleStabilizer
   int _forceOverwrite;
   int _currentReadingIdx;
   double _lastOutputValue;
+  double _lastCodeValue;
+  int _abortCounter;
 
   /*!
-   * @brief Returns the average
-   * @return Returns the average of the moving window
+   * @brief Returns the M-2 average
+   * @return Returns the M-2 average of the moving window
    */
   double getAvg();
 
-  /*!
-   * @brief Returns true if moving window contains monotone elements 
-   * @return True if all elements have the same value
-   */
-  bool isBufferMonotone();
-
 public:
   /*!
    * @brief Construct a new Scale Stabilizer object