The motorized window blinds



The two story family room showing most of the 8 blinds in the background
that are the subject of this project.


Two of the eight blinds that are motorized
(this animation will run 7 times)

I built a system using two motors to actuate the eight window blinds in my two-story family room. The system consists of pulleys placed under the family room floor, limit switches, gear motors, and the electronic circuitry needed to control the system.

Some of the requirements that I set for myself in this design are:

  1. the ability to remove the hardware without scarring the home.
  2. the ability to easily operate the blinds in the normal manual way.
  3. the motors and machinery must be hidden from view.
These were accomplished by using a steel cable and hiding the hardware in the recreation room in the basement below.  A 'S' hook connects the steel cable with the pull cords so that they can easily be disconnected from the motor drive.  All you can see from the family room is a steel cable disapearing into the carpet.

The gear motors were purchased from Grainger Industrial Supply (similar to part no. 2L003). With a 6" diameter pulley, they can provide 30lbf of pull on the steel cable. I had previously measured that about 21 lbf was needed to pull the blinds when they are in the almost fully open position, when the amount of weight on the pull cord is the highest.

The travel of the system is governed by limit switches near the ceiling and floor of the rec room below. The motor stops when the shuttle hits the switch, and can only go in the opposite direction. Control of the system occurs by direct X-10 commands. In other words, each of the two motors is assigned a unit code. Sending an ON to that address causes the associated four blinds to open until the shuttle hits the limit switch. The opposite occurs when an OFF command is sent. When an ON is sent to a third address, both motors halt, allowing me to set the blinds to any position.



As mentioned above, the four blinds attach to their corresponding actuating cable by an 'S' hook. This allows us to disconnect the motor drive by unlooping the pull cord from the 'S' hook, and actuate the blinds manually. The type of blind we have is the 'Symphony' double-cell blind by Comfortex. It does not lock if you pull the cord straight down, but locks when you pull sideways. Thanks to this, the motor can raise or lower the blinds unobstructed by the cord locks.

The system has been in use for several years now, and performs well. Since the motors are one floor below, there is very little sound while the blinds are moving. The only problem occurs when occasionally (about twice per year) one of the cord locks stick while the system is trying to lower the blinds. In that case that one blind stays open, and needs to be released manually.

Other construction methods that I have seen use modified cordless drill motor assemblies for the motor. These should work quite well also.




Schematic of the circuitry.  Note that it was designed before I knew
how to program microcontrollers.  Click to view full size.


Detail of the interface between the steel pull cable and the blind cords.
I crimped an eyelet onto the cable, and looped an 'S' hook onto it.
This allowed me to hook the standard blind cords
so that they could be easily removed in the future.


Picture of the two pulleys under the family room floor.


The motor and limit switch assembly.  Note the limit switch at the top of the
picture.  It is mounted on a bracket with a long slot so that the travel of
the shuttle can be adjusted.  Above the switch is the shuttle.  Prior
to mounting the motor, I had mounted a wooden board against the
wall so that I would have freedom in mounting the bracket of the
motor depending on how the line hung down from the ceiling. 
A third limit switch later added to the system can be
seen right next to the pulley.

Repairing cord locks on these blinds
By 2013, I had gathered enough broken cord locks that I decided to investigate ways of repairing these.  The blinds that I have are from the Comfortex brand, and the model is Symphony.  They have a double layer of honey comb cells.  The bracket that holds these blinds to the top beam are OEM part number 307E, and the cord lock is OEM part number 708.  By 2013, I could no longer find anyone that stocked these.

307E bracket for Symphony blind708 Cord Lock for Symphony
The top metal bracket and cord lock for the shade.  Images from blindsparts.com

Over the years, these cord locks are damaged by the cords cutting into the soft plastic, this prevents free movement of the cord along the opening.  I decided to try and armor these with some metal wire.  The photo below shows this kind of damage on a lock that was used on the left hand side of the blind.

damaged cord lock
Damaged cord lock (circle).  Note there is similar damage to the other side,
which occurred when this lock was used on the right hand side of a blind in a past application.

Start by using a metal saw, and cut a groove just above the base plastic.

Modified lock
Groove cut into the side of the lock with a hack saw.

With wire installed
Installation of the reinforcing wire.  

Install a doubled piece of small paper clip wire into the groove that was just cut so that the bend is sticking out a tiny amount on the left hand side.  Cut the outer wire so that it is just flush with the wall of the lock chamber.  The inner one can be left long as shown above.  The idea is to have the cord drape along this wire so that it can no longer cut into the plastic.  Once installed, apply a small dab of hot glue to the right hand part to secure it.  Ensure that the wire extends far enough out to prevent the cord from falling into the groove previously cut by the cord.

another rev
Another revision of the wire (5/2013).

Another issue is that the cord sometimes gets under the triangular cam of the lock.  I noticed the cam is often a little loose and this allows the cord to get under it.  To prevent that, I added a circular cardboard shim on top of the cam, shown above.  That seems to be very effective in reducing problems.

Replacement cords
I have found that cords used by Hunter Douglas on the Duette and Applause line are an effective replacement for the cords on my blind.  Their cord goes by the name "Ultrawear".

Project Log

  • December 1991.  Purchased blinds.
  • September 1993. System designed, built and installed.
  • 1996.  Added a third limit switch near the pulley of the motor to sense when the cable is slack.  This stops the motor just as the top limit switch would and prevents the cable from winding backwards on the spool.
  • May 2004.  I updated this page by taking the two pictures of the hardware above.  After more than 10 years of use, the hardware's design has shown to be robust and has stood the test of time despite daily use.
  • August 2004.  This hardware is featured in the book "Home Automation Hacks".
  • November 2004.  After a few request over the years, I decided to put the schematic on this page.
  • January 2007. With daily use, the left motor gearbox wears out.  I purchase two new ones for $85 (with shipping) from servocity.
  • March 2013.  Added note to repair cord locks.  Long term update will follow.

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