MPX5700AP to PSI for Arduino

mpx5700ap.ino

float getPressure(int raw) {
  // raw 0-1023, get from analogRead();
  // 0.004887586 is from 5v/1023
  // General info:
  // range of voltage reading is 0V-5v
  // the sensor outputs 0V or +ZPO to (0v or ZPO)+4.5V, while the range is 4.587v - 4.7v - 4.813v
  // each KPa is 6.4mV or 0.0064V
  float voltage = raw * 0.004887586;
  // Initializing pressure variable as float
  float pressure = 0.0;
  // 0.184v to 0.409 ZPO, we choose the middle one
  float zeroPressureOffset = 0.2965;
  
  // 0-4.6v reads 0-700KPa, the rest is 100KPa over 0.3V
  if (voltage < 4.6) {
     // pressure = voltage * 700.0/4.6; it raises 700KPA over 4.6 volt
     // with compensation: pressure = (voltage - zeroPressureOffset) * 700.0/4.6;  
     // without compensation: pressure =  voltage * 152.173913;
     pressure = (voltage - zeroPressureOffset) * 152.173913;
   } else {
     pressure = 700.0 + (voltage-4.6) * (100.0 / 0.3);
     // last piece raises 100KPa over 0.3 Volt.
     // can be optimized to   p = c1 + v * c2
   }

   return pressure * 0.145037738;   // convert KPa to PSI
}