Fidget Spinner Tachometer

/*
 * Fidget Spinner Tachometer
 *
 * learnelectronics
 * 11 JUL 2017
 *
 * www.youtube.com/c/learnelectronics
 * arduino0169@gmail.com
 */




#include <Wire.h>                                                 //I2C library for OLED
#include <Adafruit_SSD1306.h>                                     //driver for OLED

#define OLED_RESET 4                                              //OLED reset on pin 4

Adafruit_SSD1306 display(OLED_RESET);                             //create instance of Adafruit_SSD1306 called display


const int hallSensorPin = 2;                                      // connect the hall effect sensor on pin 2
const unsigned long sampleTime = 1000;                            //sample time 1000mS or 1S
const int maxRPM = 1500;                                          //just a guess
int rpmMaximum = 0;                                               //var to store new maximum rpms

void setup()
{
  display.begin(SSD1306_SWITCHCAPVCC, 0x3C);                      //start the OLED @ hex arrdess ox3c
  display.display();                                              //send data in bufer to screen
  display.clearDisplay();                                         //clear buffer and display
  pinMode(hallSensorPin,INPUT);                                   //set digital pin to as input

  display.setTextSize(1);                                         //display params
  display.setTextColor(WHITE);                                    //display params
  display.setCursor(0,0);                                         //display params
  display.print("Initializing");                                  //send message to buffer
  delay(1000);                                                    //wait
  display.display();                                              //send data in bufer to screen
  display.clearDisplay();                                         //clear buffer and display
}

void loop()
{
  delay(100);                                                     //wait 1/10 of a second
  int rpm = getRPM();                                             //int var called rpm equal to val returned by func getRPM
  if (rpm > rpmMaximum) rpmMaximum = rpm;                         //check for new max rpms
  displayRPM(rpm);                                                //call displayrpm func


}

int getRPM()                                                      //function to get rpms
{
  int count = 0;                                                  //set int var count to 0
  boolean countFlag = LOW;                                        //set count flag to 0 (off/false)
  unsigned long currentTime = 0;                                  //set current time to 0
  unsigned long startTime = millis();                             //set startTime to current millis
  while (currentTime <= sampleTime)                               //as long as currenttime is lessthan sampletime
  {                                                               //check hal sensor
    if (digitalRead(hallSensorPin) == HIGH)                       //if high (1/ON)
    {
      countFlag = HIGH;                                           //set or keep countflag high
    }
    if (digitalRead(hallSensorPin) == LOW && countFlag == HIGH)   //but if it's low (hall triggered)
    {
      count++;                                                    //increment count by 1
      countFlag=LOW;                                              //set flag low
    }
    currentTime = millis() - startTime;                           //new current time is current millis - starttime
  }
  int countRpm = int(60000/float(sampleTime))*count;              //do da maths
  return countRpm;                                                //return the rpms
}

void displayRPM(int rpm)                                          //displayrpm function
{

  display.clearDisplay();                                         //display params
  display.setCursor(0,0);                                         //display params
  display.print("RPM: ");                                         //send title info to buffer
  display.println(rpm,DEC);                                       //send rpm data in decimal format to buffer
  display.print("Max RPM: ");                                     //send title to buffer
  display.print(rpmMaximum, DEC);                                 //send maxrpm data in decimal to buffer
  display.display();                                              //show me the buffer!
}