Pitot airspeed meter on an Arduino Uno

// Pitot airspeed meter: an NXP MPX5010DP differential pressure sensor on a
// pitot tube, and the airspeed on a 16x2 I2C LCD.
//
//   A0      the MPX5010DP's VOUT (pin 1; pin 2 GND, pin 3 VS on 5 V)
//   P1      the pitot tube's tip, facing the wind (the marked side's port)
//   P2      the static holes on the side of the tube
//   LCD     SDA -> A4    SCL -> A5    VCC -> 5 V    GND -> GND
//
// The air rammed into the tip is at a higher pressure than the air sliding
// past the side holes, by half the air's density times the speed squared
// (Bernoulli). The sensor reads that difference:
//
//   VOUT = VS x (0.09 x P + 0.04)      P in kPa, 0 to 10 (the datasheet)
//
// so the sketch works in fractions of the supply, which the Uno's converter
// measures against too. A real part's zero can be anywhere from 0 to 0.425 V,
// so the sketch measures it at power on, with no wind, and subtracts it.
//
// One converter step is 10.9 Pa: about 4 m/s at the bottom of the scale and
// a fraction of a m/s at 30 m/s, which is why pitot tubes read nothing at a
// walking pace.

#include <Wire.h>
#include <LiquidCrystal_I2C.h>

const float AIR_DENSITY = 1.204;    // kg per cubic meter, 20 C at sea level

LiquidCrystal_I2C lcd(0x27, 16, 2);
float zero = 0.04;                  // the fraction of VS at no pressure

float readFraction() {
  long sum = 0;
  for (int i = 0; i < 32; i++) sum += analogRead(A0);
  return sum / 32.0 / 1023.0;
}

void setup() {
  Serial.begin(115200);
  Serial.println("Mokxi Arduino Uno: pitot airspeed meter");
  lcd.init();
  lcd.backlight();
  lcd.print("Zeroing...");
  delay(100);                       // the sensor's 20 ms warm up, and more
  zero = readFraction();
  Serial.print("Zero: ");
  Serial.println(zero * 5.0, 3);
  lcd.clear();
}

void loop() {
  float kpa = (readFraction() - zero) / 0.09;
  float pa = kpa * 1000.0;
  if (pa < 0) pa = 0;
  float speed = sqrt(2.0 * pa / AIR_DENSITY);  // m/s

  lcd.setCursor(0, 0);
  lcd.print(pa, 0);
  lcd.print(" Pa        ");
  lcd.setCursor(0, 1);
  lcd.print(speed, 1);
  lcd.print(" m/s  ");
  lcd.print(speed * 3.6, 0);
  lcd.print(" km/h  ");

  Serial.print("Pa: ");
  Serial.print(pa, 0);
  Serial.print("  m/s: ");
  Serial.println(speed, 1);
  delay(250);
}