Guidance for making photocell and 12v relay on timer

[irishluck]

So I've been trying to do my own research on this.But just confusing myself.
I figured this would be simple enough to do so maybe someone on here can point me in right direction and help me.

Basically I'm helping out a school with a project.
Main reason I'm doing it is because I'm a a laser person and know how to build them

So this is what I have.

I will have a light shining on a photocell, when the light is broken I need it to trip a relay for probably just 30 seconds. There will be a 24VAC line coming into the project box which will be split. The circuit board will run from a 12VDC line that has been converted from the 24VAC.

a friend mentioned to me about using a 555 timer. Says there reliable, easy to use and cheap.

So can someone kind of help me out with this on what I need to do to build this circuit?

Thanks in advance.

 

[(*steve*)]

Something like this would be the core of your circuit.

http://cdselectronics.com/Kits/Timer Relay.htm

I'd build it first and see if you can make it do what you want using the switches as a trigger. If you can, it's time to make a trigger circuit using "photocell"

What are you using to detect the beam of light?

 

[irishluck]

Something like this would be the core of your circuit.

http://cdselectronics.com/Kits/Timer Relay.htm

I'd build it first and see if you can make it do what you want using the switches as a trigger. If you can, it's time to make a trigger circuit using "photocell"

What are you using to detect the beam of light?

What kind of switches are on that circuit? I basically have to have a photocell in this.
Where would I put that on the board.

It will be a high power laser.

So the 100k trimpot is what will tell the relay how long to stay tripped for?
Is says this one can only do like 12 seconds. What would I need to do 30 seconds?