calculate pressure trend

src/SensorHistory.cpp

@@ -0,0 +1,77 @@
+#include "SensorHistory.h"
+
+#include <Arduino.h>
+
+//static const char *TAG = "SensorHistory";
+
+SensorHistory::SensorHistory(const int size) {
+  _size = size;
+  _values = (float*) malloc(_size * sizeof(float));
+  clear();
+}
+
+SensorHistory::~SensorHistory()
+{
+  if (_values != NULL) free(_values);
+}
+
+void SensorHistory::clear(void) {
+  _index = 0;
+  _cnt = 0;
+  for (int i = 0; i < _size; i++)
+  {
+    _values[i] = 0.0; // keeps addValue simpler
+  }
+}
+
+void SensorHistory::addValue(const float value) {
+  if (_values == NULL) return;
+
+  _values[_index] = value;
+  _index = (_index+1) % _size;
+
+  if (_cnt < _size) _cnt++;
+}
+
+float SensorHistory::getAverage(void) const {
+  if (_cnt == 0) return NAN;
+  float sum = 0;
+  for (int i = 0; i < _cnt; i++) {
+    sum += _values[i];
+  }
+  return sum / _cnt;
+
+}
+
+float SensorHistory::getMin(void) const {
+  if (_cnt == 0) return NAN;
+  float min = _values[0];
+  for (int i = 0; i < _cnt; i++) {
+    if (_values[i] < min) min = _values[i];
+  }
+  return min;
+}
+
+float SensorHistory::getMax(void) const {
+  if (_cnt == 0) return NAN;
+  float max = _values[0];
+  for (int i = 0; i < _cnt; i++) {
+    if (_values[i] > max) max = _values[i];
+  }
+  return max;
+}
+
+float SensorHistory::getElement(int index) const {
+  if (_cnt == 0) return NAN;
+  index = (_index-1 - index) % _size;
+  if (index < 0) index = _size+index;
+  if (index >= _cnt) return NAN;
+
+  return _values[index];
+}
+
+float SensorHistory::getFirst(void) const {
+  if (_cnt < _size) return _values[0];
+  return getElement(-1);
+  
+}

src/SensorHistory.h

@@ -0,0 +1,26 @@
+#ifndef _SENSOR_HISTORY_H
+#define _SENSOR_HISTORY_H
+
+class SensorHistory {
+  public:
+    explicit SensorHistory(const int);
+    ~SensorHistory();
+    void clear();
+    void addValue(const float);
+    float getAverage() const;
+    float getMin() const;
+    float getMax() const;
+    float getElement(int) const;
+    float getFirst() const;
+    int getSize() const { return _size; };
+    int getCount() const { return _cnt; };
+  protected:
+    int _size;
+    int _index;
+    int _cnt;
+    float* _values;
+};
+
+
+
+#endif /* _SENSOR_HISTORY_H */

src/main.cpp

@@ -31,6 +31,8 @@
 #include "network/XD0OTA.h"
 #include "network/XD0MQTT.h"
 
+#include "SensorHistory.h"
+
 #include "icons.h"
 
 extern "C" {
@@ -66,6 +68,8 @@ struct __attribute__((packed)) sensor_readings_t {
 
 sensor_readings_t sensors_a4cf1211c3e4, sensors_246f28d1fa5c, sensors_246f28d1a080, sensors_30aea47b0568;
 
+SensorHistory history_pressure(30);
+
 uint32_t lastDisplayUpdate = 0;
 bool bme280_active = false;
 bool bme680_active = false;
@@ -148,6 +152,8 @@ void getSensorMeasurements() {
     sensor_readings.temperature_min = sensor_readings.temperature;
   }
 
+  history_pressure.addValue(sensor_readings.pressure / 100.0F);
+
   if (uv_active) {
     sensor_readings.uvi = uv.readUVI();
     sensor_readings.uva = uv.readUVA();
@@ -264,6 +270,24 @@ void displayValues() {
     display.setFont(&FreeSansBold9pt7b);
     display.setCursor(135,y_offset+40);
     display.printf("%.1f", sensor_readings.pressure / 100.0F);
+    float pressure_diff = history_pressure.getElement(0) - history_pressure.getFirst();
+    display.setFont(NULL);
+    display.setCursor(135,y_offset+45);
+    if (isnan(pressure_diff) || history_pressure.getCount() < history_pressure.getSize()) {
+    } else if (pressure_diff > -20 && pressure_diff < -1.1) {
+      display.print("Trend: --");
+    } else if (pressure_diff < -0.2) {
+      display.print("Trend: -");
+    } else if (pressure_diff < 0.2) {
+      display.print("Trend: =");
+    } else if (pressure_diff < 1.1) {
+      display.print("Trend: +");
+    } else if (pressure_diff < 20) {
+      display.print("Trend: ++");
+    } else {
+      display.print("?");
+    }
+
 
     // Other
     display.drawRect(195,y_offset+10,56,122-10,GxEPD_BLACK);