noob question

I am fairly certain that a PLC will solve my woes, but there seem to be so many to chose from. Perhaps one of you experienced types can direct me to a proper fit?

Task: To automatically lower a projector screen when the projector comes on.

Details: The projector sends out a 12v trigger signal when on and the signal is removed when off. I already have a screen controler that handles raising and lowering via remote. This controler has 3 inputs; Common, Up and Down. Closing the circuit between Common and Up raises and likewise for Common and Down. The circuit only has to be closed momentarily to get the screen in motion. The screen takes care of stopping at the correct position.

So, what I am after is the ability to sence the 12v signal and lower the screen and then raise it when the 12v source is removed.

I would like to close the up/down circuit for only about half a second; just enough to get it moving.

I have tried to come up with a component diagram to go to Radio Shack and get transistors and such to do it, but I am not an electrician and couldnt come up with something that wouldn't burn my house down. So I figure, being a programmer, that a PLC sounded like an easy approach. After reading the tutorial on this site, I realize it is WAY more than I need, but still seems viable. Any thoughts or suggestions are welcome.

Thank you in advance for any assistance.

J

Have you thought about doing this with a couple of relays and a timer? Save yourself a lot of money.

I would like to close the up/down circuit for only about half a second; just enough to get it moving.

Click to expand...

What happens if this is maintained?
If you can tolerate a maintained signal , you could use a standard relay (about $10.00)

I have, but not being an electrician, I haven't been able to come up with a solid solution. Activating the screen when the projector came on wouldnt be so hard, but having it go back up when the 12v signal was removed wasn't something I could figure out. I was thinking of using the 12v signal to charge a cap and using that to activate the "up" relay when the 12v source was removed, but never really figured it out.

As for the maintained part, first, I don't know what effect it would have on the circuit. Second and most important, it would render the remote useless.

If I ever wanted to raise or lower the screen and either circuit was continously closed, then it wouldnt respond to the remotes signal as it would get overwritten right after.

why not just use a single pole relay , and use Nc contacts to give sig for screen up , then No for screen down.A simple car relay will do this for you.As said before as long as the control can stand constant sig for screen up you will be ok.

I've never used them, but a quick google search resulted in this possible solution:
http://www.smarthome.com/7279.html

a little omron timer relay - HY4 I think they're called - different voltage and time ranges available off the shelf (uk), bound to be something similar in us.

Devils advocate

From your post
It seemed that what you have now is working just fine.
It sounded as if you were happy with it.

If it ain't broke don't fix it !! ??

What are you going to gain with a PLC that you do not already have.

UNLESS you are like me and like to do new things.

Dan Bentler