Can I place a relay at the output pin of a 555-timer
To elaborate on Peter Bennett's answer, here is the standard relay driver circuit I use. It removes the requirement that the 555 can supply the full current of the relay.







simulate this circuit &ndash; Schematic created using CircuitLab

Notes:


Relay power doesn't have to be the same power supply as the rest of the logic, but it can be if that is adequate voltage for the relay. Ensure the relay power supply voltage is adequate to close the relay.
Select Q1 for adequate relay drive current. For large relays, the 3904 may not be appropriate. Also ensure that the device will saturate. A darlington connection may be required for very large currents.
D1 is a flyback diode required to protect Q1 from voltage spikes caused by the relay coil.