Radio station WWV uses a 5 ms long pulse of 1000 Hz (i.e. 5 cycles) to make the sound of a "tick". I tested it with an 8ohm speaker (with 150 ohm resistor in series) and this code:
// Change this to the output pin you are using
#define TICK_PIN 17
void setup()
{
pinMode(TICK_PIN,OUTPUT);
for(int i = 0;i < 5;i++) {
tone(TICK_PIN,1000,5);
delay(1000);
}
}
void loop()
{
}
Sounds pretty good, although 3ms sounds better on the speaker I am using.
Pete