Project time ! : Automatic curtain opener/closer.

I did see some other projects for closing and opening (automatically) the curtains, I certainly wanted to build one myself now.

Most other designs I saw were built using a fishing line. I did not want to use a fishing line, because fishing lines always will break at some point ?

For this automatic curtain I used a teethed timing belt (with metallic enforcement, so very strong) and a timing pully wheel (20 teeth), which are also used for some 3d printers.

Aim was that the curtains will open and close automatically, when it gets light or dark, and a manual override of course. I considered a timer too with a RTC, but so far this works fine now, without a RTC.

(for a collecion of fotos and movies, I created a shared album :

https://photos.google.com/share/AF1QipNMP3QPAfzsXe...

Also, see the short manual and this video of the end result :

close-open-curtains-2

Step 1: Materials and Tools You Need

Step 1 :

Gathering all the stuff you need. This could vary in other situations.

The materials I used :

The components

“Mechanical” :

Timing belt for 3d printers : 3
or 6 meters, depending on the size of your window/curtain.

(example : if your curtain has to cover 1.5 meters, you need a belt of 3 meters)

(ordered this at AliExpress : GT2 belt width 6 mm RepRap 3D printer 10 mtr.)

20 teeth pulley wheel

(ordered this at AliExpress : GT2 Timing Pulley 20 teeth Alumium Bore 5mm fit for GT2 belt Width 6mm RepRap 3D Printer Prusa i3)

Smooth (no teeth) axis wheel (or a second free rolling pulley wheel)

Wood 20x10x1.8 cm

Wood 2x2x6 cm

Aluminium strips with slide hole (sometimes these are used for aligning picture frames on a wall, I had them lying around somewere)

Some 5mm nuts and bolts

Some 3 mm nuts and bolts

Some screws and plugs for attaching to the wall

Aluminium plate 0.2x2x30cm, cut 4 strips from 2x1.5 cm

Electrical stuff :

Arduino Uno R3

Power suplly 12V 2A (depending on what motor you use)

Motor with gear (60 to 120 rpm)

Motor driver L298n

Small circuit board 3x2.5 cm

3 Leds

3 resistors 220 or 330 ohm (current limiting resistors for LEDs)

LDR

1 resistor 330 Ohm (analog divider with LDR)

4 resistors 10K (pull up resistors for switches )

Some headers for small circuit board

Wires (Dupont/Arduino wires), male-male – male-female

Case (115x90x55)

Switch with three positions on/off/on

2x (small) Reed Relays with magnets

Heat Shrink tube/wire

Tools used :

Solder Iron / Solder

Drill

Saw

Screwdrivers

Hot Glue

Pliers

Wire Stripper

Scissor

Patience

Step 2: Steps Creating the Modules

Step 2 :

First, I planned to make things as modular as possible : Motor rig, second axis rig, Arduino, motor controller, connector interface, case.

I started with creating the motor rig and connector (for connecting the motor, reed switches and LDR to the controller via a RJ45 connector) on a crafted piece of wood.

The whole depends a bit on what kind of motor you have/use, but key is that the belt driven by the pulley wheel is very near the rails of the curtain (about 1 to 1.5 cm. next to it).

I had a couple of motors with gears lying around, which I saved long time ago from a professional coffee brewer. They were 24 volts with a gear which reduces the RPM of the motor to about 120 RPM when on 24 volt. I use the motor on 12 Volt here, so geared RPM is about 60. I used 12 V because the Arduino is powered also with the power supply I had for this project, and to reduce the max. wattage for the connector (see more on that below).

Attach the teethed pully wheel to the axis of the motor/gear. The axis of the gear was 6 mm, the pully wheel 5 mm. so I needed to drill the hole of the pully wheel larger to 6 mm.

Then created a mount for this given motor, cutting out the wood so the motor and gear would fit in nicely and to be able to mount the Reed switches next to it, and attach it to the wall with two plugs and screws.

Next I used a RJ45 connector (female), to connect all the wires from the motor and two reed switches and a LDR. The eight wires (4 pairs) in a network cable are just enough to do the job.

The motor only draws between 0.1 and 0.3 amps (with 12 Volts, 1.2 to 4 watts) (depending on the load it gets from the curtain). A single wire in a Network cable (at least in the ones I have) can easily maintain 10 watts. As a matter of fact, PoE standard is 15 watts per pair, but you need a good certified PoE cable too then.

And the used length of the cable is only about 2 meters. This was my main concern though : Will the wiring for the motor be able to carry the wattage the motor needs. So far, no problems, no heating up of connections or wires, and I built in a software safety : The motor can and will only run for a maximum amount of given/defined time (30 to 50 seconds, also again depending on how long it will take to close or open the curtain). You need to tweak this for you own situation.

If this runtime is exceeded, the motor will stop and not be driven again by the motorcontroller. The reason for the exceeded runtime then needs to be investigated and solved before you reset the Arduino/controller (just unplug/plug the power cable to reset).

A straight one to one network cable would be ideal, but most ethernet cables (if not all) will have a twist in the connector, so the coloured wires you use on one end, will not be the same on the other end, if you know what I mean. You have to keep track accurately of how you wire things up.

Two pairs I could use as they were, the orange and brown pairs were the same on both ends, but the blue and green pair on one end, became a mix of the two on the other end. No Problem, as long as you know what combination of colours is hooked up to what on the other end.

Step 3: Creating the Second Axis

This is a simple step : see the pictures. Create a small second axis rig for the belt to run on, I used an aluminium strip with slide hole which makes it easily possible to put the correct tension on the belt easily. Attach it near the rail on the other end of the curtain/window. See photo.

Thus, with a small wooden block, aluminium strip with slide strip, 5mm bolt and 2 nutts put together that thingy in the photo, and drill holes to attach to the wall with some plugs and screws near the rail on the right end of the curtain.

Step 4: The Belt

The belt :

This really needs to be done precisely. Because I used adjustable axises and reed switches, I created some margins, but the length of the belt needs to be quite exact, and the location of the magnets and clips even more.

I bought this belt from AliExpress, 10 mtr reinforced teethed timing belt (for 20 teeth pulley wheel (also from/via AliExpress)), costed only 7.60 Euros.

In the end, I used up all 10 meters, one for a 3 mtr wide curtain (so I needed approx. 6 meter of this belt), and another one for a smaller window, a 1.7 mtr wide curtain, so another 3.4 mtr used

To get the exact length of the belt, you need to mount the motor rig and second axis rig to the desired places on the wall. Wrap the belt with enough tension around the wheels and cut the belt.

In the 4 aluminium strips of 0.2x1.5x2 cm drill 3 mm holes. Clamp two strips on top of each other, and drill three holes (so the holes are nicely alligned, to put the bolts through later on). Two holes on the edges/ends and one somewhere in the middle, but make sure the belt can move between two holes. This is to attach one set of strips to the belt for one end of the curtain, and the other two aluminium strips are used to attach/clamp the two ends of the belt together with the help of a small piece of belt 1.5 cm long (see photos).

This connection thus serves two purposes, connect the belt ends to make a loop, and act as the one of the two curtain attachments. Tighten the nuts on this clip firmly, so the belt is strong enough to pull and push the curtain. The force is not that much, 2 to 3 kg at most (unless there is something going wrong ?!) .

The other clip should not be tightened yet, as the position of this clips needs to be adjusted for the other curtain later.

Once the belt is finished, wrap it around the pully wheel and axis wheel and tension the belt firmly with the adjustable axis/aluminium strip on one end.

Don’t attach the curtains yet to the clips, you need to test and adjust everything correct before you can attach the curtains.

The clip which is not the "loop" connection should thus still be “slidable”.

Step 5: The Arduino, Motor Controller and Interface Board

The Arduino, motor controller and interface board.

For modularity, I used a small interface board (PCB) to create the necessary headers and resistors for pull up and for the LDR divider, and then connect with female headers all the wires of the RJ45 connector and manual override switch.

In the end, the interface board is maybe a weak point in the whole, and was maybe unneccesary, and direct connections where perhaps better and easier.

The pins allocation on the Arduino is as follows ;

// pins allocation :

// A0 - LDR

// 0 + 1 - Serial printing

// 2 - led green

// 3 - led red

// 4,5 - motor driver L298n

// 6,7 - FREE

// 8 - Top reed switch - close(d)

// 9 - bottom reed switch - open(ed)

// 10 - Manual switch open

// 11 - Manual switch close

// 12 - FREE

// 13 - blink alive led (external Yellow)

Connect all the wires to the interface board via the Arduino wires (male-female) according to the pin alocations above.

Solder the 3 leds with the anode (long leg) + resistor to the pins 2,3 and 13 of the Arduino, and the cathodes to ground.

I used :

Pin 2 to Green, for indicating curtain opening. (left curtain to the left seen from front)

Pin 3 to Red, for indicating curtain closing. (left curtain to the right seen from front)

Pin 13 to Yellow for alive blinking (Yet, I did not use this anymore, as a blinking led in the dark can get annoying, but it is there to use ?, I programmed the led not to be really used, on the other hand, using the DARK or LIGHT indication for blinking only during the day, is easily possible too).

As a matter of fact, programming this all went along building this controller. The idea of the red and green led came later, and the use of the/a yellow became less/not important.

Step 6: Putting It All Together

Built the case. The case which is CASE115x90x55MM on the outside, on the inside it was a bit smaller (107x85x52,

Drill 5 mm holes for the Leds, a 6 mm hole for the switch, a 6 mm hole for the connector wire/network cable, and holes for the Arduino power connector and USB connector (which is easy for programming/updating the Arduino)

Also, solder two wires from the Arduino power connector to the motor controller. The arduino is powered via this external power connector, and so is the motor controller.

Put the Arduino, motor controller and PCB in the case and connect all wires (LED'S with 220 ohm resistors, switch with pull up resistors, and also lead the ethernet cable though the hole to the PCB and connect to the headers.

Attach the motor rig to the wall on the left side of the window, the second axis wheel to the right side of the window, put the belt around the pulley wheels, connect the ethernet cable to the RJ45 connector on the motor rig, power up the Arduino with only the USB at first.

Upload the program/firmware "curtain-2.ino", and test the LED values and reed switches, and manual swith via the Arduino IDE Serial monitor output. Special care for first tests, depending on how you wired the motor to the motor controller, the motor should turn anti-clockwise for closing the curtain, and clockwise for opening. If that is not correct, you can either cross the wires on the motor controller or PCB, or re-program the "motor_open()" and "motor_close()" function to do the opposite.(signal controller to turn clockwise or anti-clockwise).

The magnets for the reed switches should be placed at the correct strategic places. When the clip for the curtain on the right is at the correct place (thus, also far on the right, when the curtain is open), then the clip for the left curtain is far on the left (curtain open), and the magnet for the bottom reed switch should be very near on the left of the clip for the left curtain (see also video and photos).

The magnet for the top reed switch should then be on the top of the belt in the middle of the window (again, when curtain is open). The photos and video will make it clear.

The top magnet will move to the left (towards the motor rig), when closing the curtain, and should activate the reed switch, when the curtains meet each other in the middle (closed position) If the reed switch is activated too late, you have a (big) problem. The motor will try to pull the curtains together, but they already are, thus the belt will stall or slip, or the motor stalls, pulling high current. So tuning this is very important, and this also goes for the closing position of course. But anyway, tuning this did not really take that much time and effort, really.. Sticking/glueing the magnets on top and bottom of the belt needs to be precise, with the slide option of the reed switches on the motor rig, you have the margins to tune it just right : see this movie for a final test

The first movie in this shared album is a test of the belt and read switches :

https://photos.google.com/share/AF1QipNMP3QPAfzsXe...

You can use the manual swith override to test this.

Covering/uncovering the LDR you can simulate dark and light.

When the clips on the belt stop on the correct places, you can attach the curtains to the clips and enjoy the automatic closing and opening of your curtains :-)