Cinema Curtains

Hi guys!

I guess most of you have been to the cinema and see those curtains that will 'adopt' to the
aspect ratio of the current viewed media (like 16:9 for the commercials and 21:9 for the actual movie)

Well, I've got a 21:9 projection screen and would like to have a similar setup.

I've already made an app for my computer to detect the aspect ratio of the currently played media (in VLC) and I also have an idea of moving the curtains.

So, to the issue:
How could i go about detecting the position of curtains?

If something unexpected happens (power out, someone pulls on the curtains or what ever), I don't want to Arduino to just assume that the curtains is at the position where it left them.

If there is a power out, then I want the Arduino to just close the curtains when the power comes back on if I haven't closed them my self.

I was thinking of using the HC-SR04 sonic sensor to detect the position of a single curtain (as they will both be synced by the wire). But sonic sensor does not do well with fabrics at a distance, and the projection screen is just above 8 feet wide. (106" 2.35:1 screen)

Next I was thinking of a potentiometer strip, but I could not find any place to buy one that long enough.

Anyone got any idea?
I'm not totally set with the movement mechanism, so if you got an idea what will work with some other mechanism, feel free to share!

Thanks in advance!

Yes, you wan't find many linear measurement systems that long.

If the power doesn't go out very often, then perhaps a limit switch is the way to go? Just drive in one direction until the switch is hit, then you know how far to go back to get to the desired position. You could also use discrete switches for each of the aspect ratios you want - you probably only have 3 curtain positions, plus "closed" if they go that far.

You can also move the position sensing elsewhere in the system. A garage door controller has a geared system running off the main chain. It knows where the chain is because this little potentiometer is always geared to it, even when power is off.

Lastly, an ultrasonic or infrared distance sensor could be set up to travel with one of the curtains and measure the distance to the other, or to the wall.

Thanks for the ideas!

The power hardly never goes out (barely once a year), and any possible company when using the projector will be no younger then 20yo so they should know better than going around och touching my stuff.

It's more of a 'better to have and not need, than to need and not have' thing. :slight_smile:

I think i'll be going with switches along the way.
It seams easy to set up and manage.

I'll also add an additional switch:
Some kind of plate at the 'end' of both curtains what will complete a circuit when the curtains are completely closed.
So if, for some reason, the unit loses power, it will just continue to close the curtains for X sec or til that circuit closes.

I was thinking of using a stepper motor, but with the position-switches configuration I guess i could go with a regular DC motor and control it with a mosfet :slight_smile:

This is what reed switches are for - you know the ones you see attached to doors to detect when they are opened?

Windscreen wiper motors would seem to be a practical sort of motor.

if you use a cable pull system, you can add a lump on the cable without causing problems. that is if the pulleys are large enough.

my old garage door opener had two such lumps. they were set to tell the unit the door was open fully.

you could place them anywhere on the cable.

another option is to put a magnet in the curtain itself and use a magnetic field detector.
not sure if this is available as a commercial product yet :

dave-in-nj:
another option is to put a magnet in the curtain itself and use a magnetic field detector.
not sure if this is available as a commercial product yet :

A reed switch?

Paul__B:
This is what reed switches are for - you know the ones you see attached to doors to detect when they are opened?

Windscreen wiper motors would seem to be a practical sort of motor.

Yeah, I was thinking about something like that.
Maybe use neodymium magnets from some old HDD :slight_smile:

windscreen wiper motors is a good idea, haven’t decided (or researched) what motor to use yet.

dave-in-nj:
if you use a cable pull system, you can add a lump on the cable without causing problems. that is if the pulleys are large enough.

my old garage door opener had two such lumps. they were set to tell the unit the door was open fully.

you could place them anywhere on the cable.

another option is to put a magnet in the curtain itself and use a magnetic field detector.
not sure if this is available as a commercial product yet :
http://www.sciencedaily.com/releases/2012/06/120612115200.htm

Yes, cable pulling system was what I had in mind. Seams to be the easiest way.

Could a setup like this work? :slight_smile: