about lm 555

Thread Starter


Joined Oct 27, 2009
I need help about lm555... when iam using an led... i can control how many seconds I set the lm555. for example the led will emmite for 5 seconds and it will turn off. but when I use it on a relay it will on and doesnt turn off. this is my circuit..

but when I use a 5 pin relay it doesnt turn off. Thanks for the help


Joined Jul 17, 2007
Interesting; in that schematic you linked to, pin 4 of the 555 timer is not connected. It should be connected to Vcc, same as pin 8.

What voltage are you using for Vcc? (supply voltage)

What voltage is the relay coil rated for?
Do you know the relay and manufacturer's part number of the relay?


Joined Aug 7, 2008
Try connecting relay thru a diode to pin 3, anode to P3 with other R term. to ground.