tachometer

#include <Adafruit_GFX.h>
#include <MCUFRIEND_kbv.h>
MCUFRIEND_kbv tft;

#define BLACK           0x0000
#define LIGHTBLUE       0x34DF
#define BLUE            0x001F
#define VERYDARKBLUE    0x0005
#define LIGHTRED        0xF945
#define RED             0xF800
#define DARKRED         0x8800
#define VERYDARKRED     0x3800
#define GREEN           0x07E0
#define VERYDARKGREEN   0x0140
#define KHAKIGREEN      0x195B62
#define CYAN            0x07FF
#define VERYDARKCYAN    0x0145
#define MAGENTA         0xF81F
#define VERYDARKMAGENTA 0x3803
#define YELLOW          0xFFE0
#define VERYDARKYELLOW  0x3180
#define WHITE           0xFFFF
#define VERYDARKGRAY    0x2124
#define GRAY            0xA514
#define ORANGE          0xFC21
#define VERYDARKORANGE  0x4920

uint16_t g_identifier;
uint8_t OrientationTFT = 1;

float value=0;
float rev=0;
int rpm;
int oldtime=0;
int time;

void isr()
{
rev++;
}

void setup()
{
    tft.begin(9600);
    tft.reset();
    g_identifier = tft.readID();
    tft.begin(g_identifier);

    tft.fillScreen(BLACK);
    tft.setRotation(OrientationTFT);

    attachInterrupt(0,isr,RISING);
}

void loop()
{
    delay(1000);
    detachInterrupt(0);
    time=millis()-oldtime;
    rpm=(rev/time)*60000;
    oldtime=millis();
    rev=0;

    tft.setTextColor(LIGHTBLUE , BLACK);
    tft.setCursor(5, 5);
    tft.setTextSize(4);
    tft.print("___TACHOMETER___");
    tft.setCursor(5,50);
    tft.print(     rpm);
    tft.setCursor(60,50);
    tft.print(" RPM");

    attachInterrupt(0,isr,RISING);
}