Solved classic 0/1 error in source code

CHANGELOG.md

@@ -57,3 +57,23 @@ All notable changes to this project will be documented in this file.
 ### Changed
 
 - Humidity often got stuck at 100%. Heater algorithm now heats for 10 minutes and cools down for 10 minutes (was 5min/15min)
+
+## [0.2.4] - 2024-03-08
+
+### Changed
+
+- Humidity timer back to 5/15 minutes: shorter cooling times give false temperature readings.
+
+### Fixed
+
+- Classic 0/1 error in max and average calculating routine, which resulted in a buffer overflow.
+
+## [0.2.5] - 2024-03-11
+
+### Fixed
+
+- 0/1 error in max and average (again, or better said: still!).
+
+### Changed
+
+- Humidity threshold heater is now a define instead of hard coded numbers in the source.

firmware/weather_station.ino

@@ -32,6 +32,8 @@
  *             - Changed some variables to the propper standard (uint8_t, uint16_t, etc.)
  *             - SparkFun wind interrupt now calculates over 3 seconds in stead of 1 second (KNMI standard)
  *
+ * See CHANGELOG.md
+ *
  **********************************************************************************/
 #include <ModbusSerial.h>
 #include "SparkFun_Weather_Meter_Kit_Arduino_Library.h"
@@ -103,6 +105,7 @@ const int SensorStatusBitsIreg        = 14;
  * 0 = Heater algorithm (0 = disable, 1 = enable)
  */
 const int HeaterCoil = 0;
+#define HUMIDITY_THRESHOLD 92
 
 // RS-485 serial port 
 #define MySerial Serial // define serial port used, Serial most of the time, or Serial1, Serial2 ... if available
@@ -165,17 +168,17 @@ char HeaterSi7021 (float humidity)
 
   switch (state)
   {
-    // Default state: humidity is below 95%
+    // Default state: humidity is below HUMIDITY_THRESHOLD
     case 0:
       Heater = 0;
-      if (humidity >= 95) {
+      if (humidity >= HUMIDITY_THRESHOLD) {
         StatemachineTimer = millis();
         state = 1;
       }
       break;
-    // Humidity went above 95%. See if humidity stays above 95% for more than an hour, if so turn on heater
+    // Humidity went above HUMIDITY_THRESHOLD. See if humidity stays above HUMIDITY_THRESHOLD for more than an hour, if so turn on heater
     case 1:
-      if (humidity >= 95) {
+      if (humidity >= HUMIDITY_THRESHOLD) {
         if ( (millis() - StatemachineTimer) >= 3.6e+6 ) {
         //if ( (millis() - StatemachineTimer) >= 300000 ) { // short delay for testing
           Heater = 1;
@@ -191,9 +194,9 @@ char HeaterSi7021 (float humidity)
       }      
       break;
 
-    // Heater is now on, let the sensor cook for 10 minutes
+    // Heater is now on, let the sensor cook for 5 minutes
     case 2:
-      if ( (millis() - StatemachineTimer) >= 600000 ) {
+      if ( (millis() - StatemachineTimer) >= 300000 ) {
         StatemachineTimer = millis();
         Heater = 0;
         state = 3;
@@ -202,17 +205,17 @@ char HeaterSi7021 (float humidity)
       }
       TempValid = 0;
       break;
-    // Heater is now off, let the sensor cool for 10 minutes
+    // Heater is now off, let the sensor cool for 15 minutes
     case 3:
-      if ( (millis() - StatemachineTimer) >= 600000 ) {
+      if ( (millis() - StatemachineTimer) >= 900000 ) {
         TempValid = 1;            // Sensor cooled, so we can take a valid temperature reading
-        if (humidity >= 95) {
-          // Humidity still above 95%, repeat heating/cooling
+        if (humidity >= HUMIDITY_THRESHOLD) {
+          // Humidity still above HUMIDITY_THRESHOLD, repeat heating/cooling
           Heater = 1;
           StatemachineTimer = millis();
           state = 2;
         } else {
-          // Humidity below 95%, reset statemachine
+          // Humidity below HUMIDITY_THRESHOLD, reset statemachine
           Heater = 0;
           state = 0;
         }
@@ -243,7 +246,7 @@ void ReadSi7021 (void)
     if (humidity>100 || humidity<0)
       humidity = 100;
  
-    //If humidity is larger than 95% switch on heater to get more acurate measurement and prevent memory offset
+    //If humidity is larger than HUMIDITY_THRESHOLD switch on heater to get more acurate measurement and prevent memory offset
     result = HeaterSi7021(humidity);
     MeasuredData.StatusBits &= 0xFFFC;  // Reset heater status bits to zero
     MeasuredData.StatusBits |= result;  // And set the proper bits to one if there are any. The result is we copied the status bits to the register
@@ -295,9 +298,12 @@ void ReadBMP280 (void)
 int MaxOfArray (int array[], uint16_t length)
 {
   int maximum_value = 0;
-  
-  while (length--)
+
+  while (length)
   {
+    // decrement length, because 0/1 problem: if lenght = n, than last position off array is n-1
+    length--;
+ 
     if (array[length] > maximum_value)
       maximum_value = array[length];
   }
@@ -309,9 +315,12 @@ uint16_t AverageOfArray (uint16_t array[], uint16_t length)
   uint32_t tmp_value = 0;
   uint8_t tmp_length = length;
   uint16_t average_value = 0;
- 
-  while (length--)
+
+  while (length)
   {
+    // decrement length, because 0/1 problem: if lenght = n, than last position off array is n-1
+    length--;
+
     tmp_value += array[length];
   }
   average_value = tmp_value/tmp_length;
@@ -451,7 +460,7 @@ void setup() {
   mb.Ireg (SensorRainSinceMidnightIreg, 0);
   mb.Ireg (SensorSnowFallIreg, 0);
  
-  Serial.println(F("Weather station v0.2.2"));
+  Serial.println(F("Weather station v0.2.5"));
   Serial.println(F("(C)2024 M.T. Konstapel"));
   Serial.println(F("This project is free and open source"));
   Serial.println(F("More details: https://meezenest.nl/mees/"));