Motorized Horizontal Blind

Alexandre René Lemay, Cameron Ayles, and Viraaj Patel, Mechanical Engineering, University of Ottawa

The motorized horizontal blind is a complete integrated system that opens and closes a horizontal blind with a DC motor powered by two AA batteries.

The system can operate in either manual mode or switch to fully automatic mode. When manual mode is selected, the control switch operates the up or down movements only and two limits switch are installed to stop the blinds at the top and the bottom position.

When the auto mode is selected, the system is controlled by the Arduino Uno Microcontroller board and the photo sensor.

The blinds will move automatically to the up position if the photo sensor detects enough light and will stop when it reaches the upper limit switch and vice versa, if the photo sensor does not receive enough light, the blind starts its decent and operates in the down movement until it reaches the lower limit switch then the blind stops, therefore fully closing the blind. 

All the components were purchased at the local Home Depot hardware store as well as several electronics shops such has Gervais electronics, The Source, Active Tech Electronics, The Robot Shop and the Hobby House Ltd in Ottawa.

Electric, Software and Electronic Components 

The blind motor is a 6-speed gearbox motor assembly. The gear ratio selected for this project was 505.9:1.  This gives 19.9 (rev/min) with a torque of type RE 260 motor (3V) 226.1 (mN-m).

The electric motor is powered by a set of 2 AA ( 1.5 Vdc batteries) of 3Vdc total output in the manual or auto mode. 

The Arduino Uno Microcontroller Rev 3 board is use to operate the electrical relay, the photo sensor, the threshold for the light sensitivity of the photo sensor.

 The Arduino board is program using its supplied operating software downloaded from the internet and configured for this project. Also the Arduino board is powered by the Laptop computer using the USB port.

A limit switch  is located  at the top and at the bottom of the wood frame to stop the movement of the blind once it reaches it specific position.

 A double pole, double throw relay switch is wired to change the contact polarity in order to reverse the direction of the motor to open and close the blind.

 A bread board integrates all electronic components such as the relay switch, a 1.2 KOhm resistor, a photo sensor (photoresistor) and to create an H-bridge wiring design. Several jumper cables are installed from the Arduino board and the bread board making the connection assembly and the battery power source.

The photoresistor is the sensor whose resistance varies with light intensity.  It decrease in resistance as the light intensity increases.  In our microcontroller application, this resistance convertes to a voltage so that an A2D converter can measure it therefore using a voltage divider circuit. 

A voltage divider is just two resistors in series connected between a voltage supply and ground.  If  R1 is connected to the voltage supply and R2 is connected to ground then the voltage at the junction between the two resistors is:

If R1 is the photoresistor, the voltage will increase with increasing light intensity. 

An electrical switch box is used to incorporate the three switches for the system. The Power switch that turn on and off  power to the system, the rocker switch that selects either the manual or the fully automatic operation and finally the third switch for the manual operation to either raze or lower the blind.

 Mechanical Components

The blind motor is a 6-speed gearbox motor assembly. The gear ratio selected for this project was 505.9:1  this gives 19.9 (rev/min) with a torque of type RE 260 motor (3V) 226.1 (mN-m)

          The drive shaft of the motor is equipped with a plastic spool to receive the blind string as it rotates to either raze or lower the blind. A bolt is installed at the base of the blind to give it weight as it hits the limit switches.

A wood frame structure was constructed to assemble all the components of the system. The complete system is mounted on a wood frame to show how the unit would be setup in a residential  indoor operation.

Two metal brackets were installed at the top and the bottom of the gear box assembly to absorb the torque given from the motor and the weight of the blind.

The prototype was tested during assembly, installation and at completion. The manual and automatic mode operated successfully.