#Python Code to capture data points:


import serial
import mDb


class Looper():

    def __init__(self):
        username = ""
        password = ""
        host = "localhost"
        dbName = "loop_controller"
        self.db = mDb.Db(host, username, password, dbName)

        self.checkTable("ir_cal_data2", [
                            {"name": "id", "type": "INT NOT NULL AUTO_INCREMENT PRIMARY KEY"},
                            {"name": "distance", "type": "TEXT"},
                            {"name": "pin_measurement", "type": "TEXT"}])
        
        self.ser = serial.Serial(port='COM17', baudrate=9600)
        self.ser.flushInput()
        self.ser.flushOutput()

        distance = 8
        while distance < 61:
            raw_input("Press Enter when ready for next reading.  Currently at " + str(distance) + ".")
            self.log_data(distance)
            distance += 1
            
    def checkTable(self, table, data):
        try:
            self.db.beginTransaction()
            self.db.checkTable(table, data)
            self.db.commitTransaction()
        except Exception as e:
            print("WARNING")
            print(e)
            
    def log_data(self, distance):
        counter = 0
        data_raw = None
        minVal = 0
        maxVal = 0
        avgVal = 0
        firstVal = True
        while counter < 250:
            try:
                data_raw = self.ser.readline()
                data_raw = int(data_raw)
                data = {"distance": str(distance), "pin_measurement": str(data_raw)}

                try:
                    self.db.beginTransaction()
                    self.db.insert("ir_cal_data2", data)
                    self.db.commitTransaction()
                except Exception as e:
                    print("WARNING")
                    print(e)
            
                if firstVal:
                    firstVal = False
                    minVal = data_raw
                    maxVal = data_raw
                    avgVal += data_raw
                else:
                    if data_raw < minVal:
                        minVal = data_raw
                    if data_raw > maxVal:
                        maxVal = data_raw  
                    avgVal += data_raw

                counter += 1
            except Exception as e:
                print("Could not log value: " + str(data_raw))
                print(e)
                #break
        try:
            avgVal = (avgVal * 1.0) / counter
            print("Min. Reading: " + str(minVal))
            print("Max. Reading: " + str(maxVal))
            print("Avg. Reading: " + str(avgVal))
        except:
            pass
            

        
            
            

Arduino Code:

As you can see I set the intercept at 85.07 instead of the 89.92 that I got from the regression line. This shift produced better results. While my test setup doesn't allow me to gain dead on accuracy, the results were very close. This is a good fit for this sensor, and I will write an R script so that it is easier in the future to calibrate each sensor.

#include "FastRunningMedian.h"

int sensorPin = A3;
unsigned int value = 0;

FastRunningMedian<unsigned int,32, 0> newMedian;

void setup ()
{
  while (!Serial) ;
  Serial.begin(9600);
};

void loop()
{
  unsigned int xmedian;
  
  value = analogRead(sensorPin);
  newMedian.addValue(value);
  xmedian = newMedian.getMedian();
  
  Serial.print(" median=");
  Serial.println(xmedian);
  
  unsigned long x3 = pow(xmedian, 3);
  unsigned long x2 = pow(xmedian, 2);
  float distance = (-0.000001805 * x3) + (0.001796 * x2) + (-0.6168 * xmedian) + 85.07;
  Serial.print("Distance= ");
  Serial.println(distance); 
};