You can set up a 555 timer integrated circuit to produce either a series of pulses or one single pulse. Choosing the function of the 555 is a matter of connecting resistors and capacitors to particular pins.
The 555's astable mode produces a series of pulses. To set up the 555 in this mode, connect pin 1 to ground, and pins 4 and 8 to power. Connect two resistors and a capacitor in series between the power and ground rails. The values of these components determines the timing of the pulses. Connect the junction of the two resistors to pin 7. Connect the junction between the second resistor and the capacitor to pins 2 and 6. Take the pulse output from pin 3.
The 555's monostable mode produces a single pulse. To set up the chip in monostable mode, make the following connections:
Connect pin 1 to ground, and pins 4 and 8 to power. Connect a resistor and a capacitor in series between the power and ground rails. The values of these components will determine the timing of the pulse. Connect the junction of the resistor and capacitor to pins 6 and 7. Trigger the pulse by connecting a switch to pin 2. Take the pulse output from pin 3.