use median instead of average

mini-beieli-node.ino

@@ -536,13 +536,52 @@ void DoDeepSleep(uint32_t sleep_time)
   }
 }
 
+//Following functions are based on "https://github.com/dndubins/QuickStats", by David Dubins
+
+long median(long samples[], int m) //calculate the median
+{
+  //First bubble sort the values: https://en.wikipedia.org/wiki/Bubble_sort
+  long sorted[m];   // Define and initialize sorted array.
+  long temp = 0;    // Temporary float for swapping elements
+
+  for (int i = 0; i < m; i++) {
+    sorted[i] = samples[i];
+  }
+  bubbleSort(sorted, m); // Sort the values
+
+  if (bitRead(m, 0) == 1) { //If the last bit of a number is 1, it's odd. This is equivalent to "TRUE". Also use if m%2!=0.
+    return sorted[m / 2]; //If the number of data points is odd, return middle number.
+  } else {
+    return (sorted[(m / 2) - 1] + sorted[m / 2]) / 2; //If the number of data points is even, return avg of the middle two numbers.
+  }
+}
+
+void bubbleSort(long A[], int len) {
+  unsigned long newn;
+  unsigned long n = len;
+  long temp = 0;
+  do {
+    newn = 1;
+    for (int p = 1; p < len; p++) {
+      if (A[p - 1] > A[p]) {
+        temp = A[p];         //swap places in array
+        A[p] = A[p - 1];
+        A[p - 1] = temp;
+        newn = p;
+      } //end if
+    } //end for
+    n = newn;
+  } while (n > 1);
+}
+
 long my_read_average(byte gain, byte times) {
-  // highest and lowest value will be ignored
-  long sum = 0;
-  long v = 0;
-  long L = 2147483647;
-  long H = -2147483648;
   long res;
+  int const num_scale_readings = 100; //number of instantaneous scale readings to calculate the median
+
+  // we use the median, not the average, see https://community.particle.io/t/boron-gpio-provides-less-current-than-electrons-gpio/46647/13
+  long readings[num_scale_readings];  // create arry to hold readings
+
+  // highest and lowest value will be ignored
   if (config_data.debug_level > 0) {
     gCatena.SafePrintf("%010d - my_read_average, measurements: ", millis());
   }
@@ -551,22 +590,14 @@ long my_read_average(byte gain, byte times) {
   // we wait 400ms (settling time according HX711 datasheet @ 10 SPS
   delay(400);
 
-  for (byte i = 0; i < times; i++) {
-    // we wait 400ms (settling time according HX711 datasheet @ 10 SPS)
-    v = LoadCell.read();
-
-    if (L > v) L = v; // find lowest value
-    if (H < v) H = v; // find highest value
-    sum += v;
-    if (config_data.debug_level > 0) {
-      gCatena.SafePrintf("%d ", v);
-    }
-    gCatena.poll();
-    delay(WAITTIMELOADSAMPLES);
+  for (int i = 0; i < num_scale_readings; i++) {
+    readings[i] = LoadCell.read();  // fill the array with instantaneous readings from the scale
   }
-  res = (sum - L - H) / (times - 2);
+
+  res = median(readings, num_scale_readings); //calculate median
+
   if (config_data.debug_level > 0) {
-    gCatena.SafePrintf("; average (without highest [%d] and lowest [%d] value): %d\n", H, L, res);
+    gCatena.SafePrintf("; median of %d samples: %d\n", num_scale_readings, res);
   }
 
   return res;

mini_beieli_node.h

@@ -55,10 +55,7 @@ enum {
   |
   \****************************************************************************/
 
-static const int32_t fwVersion = 20200109;
-
-// wait between samples in milliseconds
-const int WAITTIMELOADSAMPLES = 100;
+static const int32_t fwVersion = 20200113;
 
 static const byte INIT_PACKAGE_INTERVAL = 100;  // send an init package every 100 packages;
 static const byte MAX_VALUES_TO_SEND = 8;