Domotics vol. 2 – Motor powered Window blind

JULY 13 2010 note:

I’ve made this project and wrote the post on 2008, that’s why I don’t mention the Computer Control. But you can build and easily wire both projects together!

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A small Introduction

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Home automation (a.k.a Domotics) brings  infinite posibilities of  intervention, controlling and monitoring household appliances even if the user is not at home. A small degree of automation is good to presuming in front of your guests, or extremely useful if you or a friend have a physical impairment.

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Ok, let’s start with a simple household device: a window blind. Adding a motor to the existing one is much better than spending money on a motor-powered replacement. For our example we’ll use a “slat type” window blind.

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Scrapping the CD unit

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Now we need a motor to pull the cord. An old CD-ROM player (donated by our friend Marcelo Diaz) contains everything we need

The CD tray opening mechanism consists on a motor and a set of gears. When the motor spins, the door opens or closes.

Take apart the unit, and cut off the engine and gearbox together (as shown on the next three pictures)

Our little motor needs 12 volts to operate. Get a 12 volt DC – 1,5 ampere wall wart to energize it.

This is how a Wall wart looks. Read the label, the output cannot be A.C. the motor will not spin

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Attaching the motor to the cord

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Cut off the knob, or any obstacle present at the end of the cord

Maybe cutting the knob created two loose cords. In that case, tie them together (like a “U”)

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Mounting the gearbox on the wall

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For God’s sake, read all the post first before drilling your walls!

Make sure that the drilling site is free of water tubes, electrical wires, etc.

Wrap the cord around the biggest gear you can find, as shown in the picture. Place the  gearbox at the exact distance to keep the cord’s tension (again, as shown). If you can energize the motor and test the movement before drilling anything, much better.

Tick the position with a pencil

Drill a pair of holes on the plastic structure

Now drill two holes in the wall, matching the previous perforations

Firmly screw the thing. If your wall is made of bricks, you must use a proper Rawlplug before the screw

The original wire is too thin. I suggest you to replace it with #16 AWG

You may paint or hide the wire, or cover the motor with a box. Is up to you.

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Electric control

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The window blind moves, that’s great, but that’s only one part of the project. Now we need a decent way to controlling it: one switch to open, another switch to close.

How ? the motor spins according to the polarity. If the polarity is reversed, the motor will spin backwards. To change the polarity without disconnecting anything or messing with wires, you need an H-Bridge.

The next schematic describes a very basic H-Bridge. I know, is very crude and requires a diode, but it works

What the hell is polarity? Where can I find a diode?I already explained that on this post

(Click to enlarge the schematic)

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I will improve this explanation as soon as I get more inspired. I’m too tired right now

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Case

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When the circuit is complete, you need a decent casing

A nice power-on led, and is done

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Finished Work

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PS: I don’t like the Beatles very much, the poster was just an improvised window shade.

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