Automated Curtains & Blinds

The objective of this project is design and build a solution to automate bioth curtains and blinds. Whilst designing a new solution to this problem, I also need a solution that can be retro-fitted into my current home. They are quite a few systems on the market at present but they are often very expensive and require a lot of work to install. Few work with the existing curtains tracks and rails you already have in your home.

Research

NOTE: Most of this has yet to be written up!

Most commercial systems on the market seem to use a 24V dc power supply. Not sure why this voltage but it is one that lends itself to storage and local power generation. Having said that, most then provide a mains power supply unit, which will not work in the event of a power cut! One reason may be to limit the current going to the motor. Suppliers like Somfy provide heavy duty motors to move curtains, weighing in at over a kilogram!

Design

There are four main challenges associated with this project:

User Interface

Having curtains that open and close automatically is one thing but there will always come a point where manual operation is required and some kind of human interface is needed. The solution most in keeping with our design approach is to use a 2-way momentary action wall switch, as this is the 'standard' input device we are opting to use. This switch can be retro-fitted to out existing home and designed into any new one.

From a control perspective, the Home Control System (HCS) will send commands to the curtain controllers but, will not maintain state. This enables human interaction to over-ride the last Home Control System (HCS) command sent. This is the model we have also adopted for lighting in our home, based upon our experiences to date.

With curtains the switch can be mounted sideways, as it makes more sense from a usability perspective and works when fitted either side of a window opening. Pressing the switch side away from the opening opens the curtains and pressing the switch side nearest the opening closes the curtains.

With blinds the switch will be mounted with normal orientation, as this makes more sense from a usability perspective and also works when fitted either side of a window opening. Pressing the top of the switch raises the blinds and pressing the bottom of the switch lowers them.

This user interface assumes you don't want to stop the curtains at some mid-point between open or closed. This is a situation we have yet to encounter, so it is not seen as a useful requirement. This also simplifies the user interface and the design.

There is no dedicated remote control being considered either. Since our Home Control System (HCS) has the ability to control the curtains and blinds, our iPhone and other remote control interfaces for the HCS can expose this functionality.

Another option currently under investigation is to use an inductive switch hidden in the wall, to make the manual user interface more subtle. Currently looking at the TapTile switches, which would be embedded in the wall and out of sight.

Power & Wiring

With a new build, installing the power and control lines to curtains and blinds is easy to achieve and plan for. With retrospective installations it is a lot more challenging, even if you factor in some redecoration. Getting power to the electric motors is going to require some work. We have assumed that 12V dc power is used to make life simpler and safer. This also ensures that things continue to work in the event of a mains power failure.

From an installation perspective, it makes sense to fit the controller behind the switch plate, to ensure easy access.

Transport

Curtains and blinds vary a lot! Some are quite light in weight and are less than 100cm in drop. Others can be made from a very heavy fabric (with lining) and drop right down to the floor (and drag on the carpet). The motors required to move them will need to be quite powerful and the gearing low enough to provide decent torque, yet not so low as to make the opening and close process take too long. We feel that three seconds is the absolute maximum time required to go from full open to fully closed (and vice-versa).

It is a requirement that the motors and mechanical elements used are very quiet in operation.

Control

Which ever way you look at it, there need to be two signal lines from the Home Control System (HCS) (unless you have a data connection to the curtain controller), one to signal close and one to signal open. The link from the controller to the motor can then be a pair of power lines, with the polarity of the dc voltage driving the motor to open and close the curtains. Whilst in theory a single control line could be used, this would only enable a permanent state to be presented to the controller and not transitions of state. This would not enable human over-ride.

In the above diagram, the starting state is with the curtains closed. Control line A is at 12V and control line B is at 0V. Switch D is operated, connecting the motor -ve to +12V. Switch C is not operated, meaning control line A (12V) is connected to motor +ve. With both the motor +ve and motor -ve at 12V, it is therefore stationary.

To open the curtains, the controller swaps the polarity of the control lines. Control line A is now at 0V and control line B is at 12V. The motor is now running in reverse and opening the curtains. As they open, switch D is operated and the motor -ve is now connected to control line B (also at 12V), so the motor continues in reverse.

When the curtains approach fully open, switch C is operated. The motor +ve is now also connected to 0V, thus stopping the motor.

Note that the a transitional state between open and closed, the motor +ve is connected to control line A and the motor -ve is connected to control line B. This is important because it means that if the Home Control System (HCS) or human operator changes their mind and switches the polarity of the power output from the controller, then the curtains will change direction as requested.

The controller will provide a soft-stop and soft-start feature, to reduce the noise of the system in operation.

Progress

The design work is progressing this month and in our garage we have rigged up a test curtain rail. We will be usign this as a test environment to try out different motors and drive configurations. The control circuit is currently being built and we have a 2-way momentary action wall switch installed to test the manual over-ride.