IR light for speed sensor

hi trying use ir light , photo transistor calculate rpms of shaft , therefore speed. keep getting zeros when displaying serial monitor.  i not sure if code or have faulty photo transistor. below code using.

#

int ledpin = 13;                
int statuspin = 12;            
volatile byte rpmcount;
volatile int status;

unsigned int rpm;

unsigned long timeold;

void rpm_fun()
{
 
     rpmcount++;
     
  if (status == low) {
    status = high;
  } else {
    status = low;
  }
  digitalwrite(statuspin, status);
}

void setup()
{
  serial.begin(9600);
 
  attachinterrupt(0, rpm_fun, falling);
 
 
  pinmode(ledpin, output);
  digitalwrite(ledpin, high);
 
 
  pinmode(statuspin, output);

  rpmcount = 0;
  rpm = 0;
  timeold = 0;
  status = low;
}

void loop()
{

  delay(500);
 
  detachinterrupt(0);

  rpm = 30*1000/(millis() - timeold)*rpmcount;
  timeold = millis();
  rpmcount = 0;
 
 
  serial.println(rpm,dec);
 
 
  attachinterrupt(0, rpm_fun, falling);
}     
#

code: [select]




int ledpin = 13;               
int statuspin = 12

const int ledpin = 13;
const int statuspin = 12;

also please put code in hash tags '#'

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