Step 4: Determine the LIMITS for the blind

Okay, so now we can tell the blind motor to go DOWN when the projector screen is going DOWN,
We can tell him to go UP when the projector screen is going UP.

But how do we know when to STOP?

When the instruction to go down is launched, I use a "delay(18000)" 18 seconds delay so that the blind is covering roughly the bottom of the mirror. Everytime it will go down, i tested it, it will arrive at the same position, but NOT exact, 1 or 2 cm different each time.

Because the position it arrives is different each time, we cannot do this when going UP, because after 2 or 3 times everything will be completely out of phase !

So we will use what is called a magnetic switch, to go UP while we didn't detect the switch closing.

It looks like this : http://www.radioshack.com/product/index.jsp?productId=2419297
It is also called a REED switch

I installed the wired part near the top of the blind on the wall, and inserted a neodyme magnet in the bottom of the blind,
so that the switch is activated when the UP position is reached.

Well done ! If you are a girl, I am impressed that you got to accomplish all this by yourself. I know many guys -self proclaimed geeks- who would never dare to do what you did !
Thanks for the comment ! <br>I'm Sorry (or not) i'm not a girl, the pics of my gf in the Valentine day's project may have fooled you ! <br>Side note, I never meet a girl who is not from the internet and does electronics ...
I'm still impressed as I haven't gotten started on Arduino myself! <br><br>I have done a few projects with MicroChip's PIC 8 bit conttrollers and your project sparked a few ideas in my head. I've noticed that most people here do stuff on Arduino and such articles are the ones with more views.<br><br>Thanks and keep up the good work.<br>
Very nice, and the most important thing in any project, it works. <br>It might have been easier to have the screen relays turn on relays for the blinds for driving the blinds up and down. Then use switches that measure the thickness of the material on the blind to act as end switches. Or, since you are using Arduino, to count the revolutions of the blind core. <br>Can you show us the installation of the motor in the blinds? Or brand of blind if the motor is factory installed?
The motor is a RC servo modified for continuous rotation, i removed the right original mount from the blind and installed the servo straight to the blind using screws / glue. <br>I shall take a picture of the motor setup if you want, but it is rather hacky :D
So that's why you must have the Arduino. To act as servo signal generator. <br>Have you thought about attaching infrared receiver to the Arduino to get it to read the signal from the screen remote? If you get one of those ultra-small and cheap Arduino clones you could have everything in very small package with very little wiring.
Yes i plan to embed a microcontroller so i can remove the need of my arduino in the project, and throw everything in a little box i can hide. <br> <br>I didn't tough about infrared receiver, that is a good idea, but i wanted to control the whole thing with the RF remote of the screen.
Very nice instructable. I hope you will follow up with the code, I want to use this to operate the gate for my animals. Thanks.
Thank you very much ! I added the code, i took the time to rename some variables and add comments to it, hope it will be useful to you !

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