How to send TTL output from Arduino Uno to Raspberry Pi?

I am trying to send TTL pulse at 1second interval to Raspberry pi? Can someone suggest me a good way to do it using GPIO or any other way possible.

Arduino Code:

void setup() {
    pinMode(12, OUTPUT);
}

void loop() {
    digitalWrite(12, HIGH);   // turn the LED on (HIGH is the voltage level)
    delay(1000);                       // wait for a second
    digitalWrite(12, LOW);    // turn the LED off by making the voltage LOW
    delay(1000);                       // wait for a second
}

Raspberry Pi Code:

import RPi.GPIO as GPIO
import time

GPIO.setmode(GPIO.BCM)
pinTTL = 4

GPIO.setup(pinTTL, GPIO.IN)

start_time = time.time()
t_end = start_time + 60
while time.time()<t_end:
    inputState = GPIO.input(pinTTL)
    if inputState == True:
        print 'HIGH', time.time() - start_time
    else:
        print 'LOW', time.time() - start_time

GPIO.cleanup()

Another thing is I have checked using multimeter, the voltage on Pi output pin does change at 1second interval.