I've put together a 555 monostable timer shown below. Running the timer using a +5V supply, without the Relay in place and mounting a LED after R1, The LED stays on for the required 30sec.

When I add the 12V relay to the circuit along with D1, Q1, R1 and relocate the LED with a 470 OHM resistor - and supplying +12V to the relay portion of the cirucut while still providing the 555 with +5V, The LED will turn on for 30 sec, but the relay will not function. If I take the relay out of the circuit, and add +12V to it while it sits on my desk, the relay functions fine.

Would the current limiting of the 470ohm resistor preventing proper function of the relay in circuit? My next step would be to jumper around the resistor & LED to see of the Relay operates. All I'm using the LED for is to provide some visual confirmation the the timer is staying on for 30sec.

Thanks for any suggestions !

 

Would the current limiting of the 470ohm resistor preventing proper function of the relay in circuit?

Yes, very much so. Take out the resistor and LED and it should work.

 

You can also move the resistor/LED between the + power supply and the collector of the transistor. It will work in parallel with the relay.

Location is everything.

 

Thanks for the comments !