add polynomial/linear ec calculation

include/ec.h

@@ -3,7 +3,6 @@
 
 #include <Arduino.h>
 
-float ecEC_ADS_CHANNEL_mean=0;
 
 bool ec_flag_measurement_available=false;
 
@@ -17,13 +16,18 @@ bool ec_flag_measurement_available=false;
 #define EC_RESOLUTION 8
 #define EC_FREQUENCY 5000
 
+#define EC_CALIB_ARRAY_SIZE 64
+uint16_t ec_calib_array[EC_CALIB_ARRAY_SIZE];
+uint16_t ec_calib_array_pos=0;
+#define EC_CALIB_READ_INTERVAL 100 //interval of reading adc value inside a measurement
+
 #define EC_ARRAY_SIZE 64
 uint16_t ec_array[EC_ARRAY_SIZE];
 uint16_t ec_array_pos=EC_ARRAY_SIZE;
 unsigned long last_measurement_ec=0;
 #define EC_MEASUREMENT_INTERVAL 10000 //complete filtered measurement every x ms
   //One filtered measurement takes EC_READ_INTERVAL*EC_ARRAY_SIZE*4
-#define EC_READ_INTERVAL 2 //interval of reading adc value inside a measurement
+#define EC_READ_INTERVAL 5 //interval of reading adc value inside a measurement
 
 #define EC_RELAY_SWITCH_SETTLETIME 500  //time until voltage of ec circuit has settled
 
@@ -36,16 +40,28 @@ enum ECState{IDLE,MEASURE};
 ECState ecstate=IDLE;
 
 float ec_adc;
+float ec_adc_adjusted; //adjusted for reference resistor
+float ec_calib_adc;
+float ec; //ec value after adjustment for reference (at current temperature)
+float ec25; //ec value but temperature adjusted for 25 degC
+
+float ec_tempadjust_alpa=0.2; //TODO
+float ec_reference_adc=5889; //adc reference value for the calibration resistor measurement
+
+//x^0*p[0] + ... + x^n*p[n]
+float ec_calibration_polynom[]={691.5992624638029,-1.4015367296761692,0.0008513503472324141,-2.2140576823179093e-07,2.8962580780180067e-11,-1.8577565383307114e-15,4.7162479484903865e-20};
+float ec_calibration_linearize_below_adc=6000; //use linear approximation below this adc value
+float ec_calibration_linear_lowADC=830; //x0
+float ec_calibration_linear_lowEC=0; //y0
 
 bool ec_measurementReady();
 void ec_startMeasurement();
 void ec_setRange(uint8_t range);
 void ec_connectProbe(bool);
 void ec_releaseRelay();
+float ec_getECfromADC(float adc);
 
 void ec_setup() {
-  //pinMode(EC_PIN_ADC,INPUT);
-
   ledcSetup(EC_PWM_CH, EC_FREQUENCY, EC_RESOLUTION);
   ledcAttachPin(EC_PIN_FREQ, EC_PWM_CH);
   ledcWrite(EC_PWM_CH, 127); //50% duty cycle
@@ -76,13 +92,14 @@ void ec_loop(unsigned long loopmillis) {
         ec_releaseRelay();
         Serial.println("Finished EC");
         ec_adc=getMean(ec_array,EC_ARRAY_SIZE);
-
+        if (isValueArrayOK(ec_calib_array,EC_CALIB_ARRAY_SIZE,0)){
+          ec_calib_adc=getMean(ec_calib_array,EC_CALIB_ARRAY_SIZE);
+          ec_adc_adjusted=mapf(ec_adc,0,ec_calib_adc,0,ec_reference_adc);
+          ec=ec_getECfromADC(ec_adc_adjusted);
+        }
 
         ec_flag_measurement_available=true;
 
-        
-        
-
         ecstate=IDLE;
       }
       
@@ -91,26 +108,33 @@ void ec_loop(unsigned long loopmillis) {
   }
 
 
+  if (ec_array_pos<EC_ARRAY_SIZE) { //measurement running
+    if (loopmillis>last_read_ec+EC_READ_INTERVAL) { //take reading into array
+      last_read_ec=loopmillis;
 
-  if (loopmillis>last_read_ec+EC_READ_INTERVAL && ec_array_pos<EC_ARRAY_SIZE) { //take reading into array if measurement running
-    last_read_ec=loopmillis;
+      if (loopmillis>ec_last_change_relay+EC_RELAY_SWITCH_SETTLETIME) { //values have settled        
+        uint16_t value = ADS.readADC(EC_ADS_CHANNEL);
         
-    //flag_print= ec_array_pos==EC_ARRAY_SIZE;
-    //ec_array_pos%=EC_ARRAY_SIZE;
-
-
-
-    if (loopmillis>ec_last_change_relay+EC_RELAY_SWITCH_SETTLETIME) { //values have settled
-      //uint16_t value=analogRead(EC_PIN_ADC);
-      
-      uint16_t value = ADS.readADC(EC_ADS_CHANNEL);
-      
-      ec_array[ec_array_pos]=value;
-      
-      ec_array_pos++;
+        ec_array[ec_array_pos]=value;
         
+        ec_array_pos++;
+      }
     }
+  }else{ //measurement not running, then take calibration readings
+    if (loopmillis>last_read_ec+EC_CALIB_READ_INTERVAL) { //take reading into array
+      last_read_ec=loopmillis;
 
+      if (loopmillis>ec_last_change_relay+EC_RELAY_SWITCH_SETTLETIME) { //values have settled        
+        uint16_t value = ADS.readADC(EC_ADS_CHANNEL);
+        
+        ec_calib_array[ec_calib_array_pos]=value;
+        
+        ec_calib_array_pos++;
+        ec_calib_array_pos%=EC_CALIB_ARRAY_SIZE;
+
+        
+      }
+    }
   }
   
 }
@@ -143,5 +167,26 @@ void ec_releaseRelay() {
   ec_last_change_relay=millis();
 }
 
+float ec_getECfromADC(float adc) {
+  uint8_t polynom_order=sizeof(ec_calibration_polynom) / sizeof(ec_calibration_polynom[0]);
+  double _ec=0;
+  if (adc>=ec_calibration_linearize_below_adc) { //adc is in range where polynomial approximation fits well
+    for (uint8_t i=0;i<polynom_order;i++) {
+      _ec+=pow(adc,i)*ec_calibration_polynom[i];
+    }
+  }else{ //low ec region. linear approximation works better here
+    float x1=ec_calibration_linearize_below_adc;
+    float y1=0;
+    for (uint8_t i=0;i<polynom_order;i++) { //get y1 value from curve
+      y1+=pow(x1,i)*ec_calibration_polynom[i];
+    }
+    float x0=ec_calibration_linear_lowADC;
+    float y0=ec_calibration_linear_lowEC;
+
+    _ec=mapf(adc,x0,x1,y0,y1); //linear approximation    
+  }
+  return _ec;
+}
+
 
 #endif

include/helpfunctions.h

@@ -13,6 +13,7 @@ float getMinf(float *parray, uint16_t psize);
 bool isValueArrayOK(uint16_t *parray,uint16_t psize, uint16_t pcheck);
 bool isValueArrayOKf(float *parray,uint16_t psize, float pcheck);
 float getFilteredf(float *parray,uint16_t psize, uint16_t pcutOff);
+float mapf(float x, float in_min, float in_max, float out_min, float out_max);
 
 
 float getMean(uint16_t *parray,uint16_t psize) {
@@ -113,5 +114,10 @@ float getFilteredf(float *parray,uint16_t psize, uint16_t pcutOff) {
   return mean/(psize-2*pcutOff);
 }
 
+float mapf(float x, float in_min, float in_max, float out_min, float out_max)
+{
+  return (x - in_min) * (out_max - out_min) / (in_max - in_min) + out_min;
+}
+
 
 #endif 

src/main.cpp

@@ -61,7 +61,17 @@ void setup() {
   //Serial.println("Setup finished");
   delay(200);
 
-  Serial.println("time,tempReservoir,EC");
+  //Test adc to ec function output
+  Serial.println();
+  for (int i=830;i<13300;i+=100) {
+    float _ec=ec_getECfromADC(i);
+    Serial.print(i); Serial.print(","); Serial.print(_ec); Serial.println();
+  }
+  
+
+  delay(100000);
+
+  Serial.println("time,tempReservoir,ECadcCalib,ECadc,ECadcAdjusted,EC,EC25");
 
 }
 
@@ -108,7 +118,13 @@ void loop() {
       Serial.print(getMeanf(tempCmean_reservoir,TEMPMEAN_SIZE)); Serial.print(",");
       //Serial.print(getMean(sm_mean,SM_SIZE)); Serial.print(",");
       
-      Serial.print(ec_adc);
+      Serial.print(ec_calib_adc); Serial.print(",");
+      Serial.print(ec_adc); Serial.print(",");
+      Serial.print(ec_adc_adjusted); Serial.print(",");
+      Serial.print(ec); Serial.print(",");
+      Serial.print(ec25);
+      
+      
       Serial.println();