Automatic opening and closing doors normally don't get much attention since they involves complex mechanisms.
But still a few innovative people have attempted to set an automatic sliding door in their bedroom.
If you are satisfied with relatively slow movement of the sliding door, you can easily install this system with the help of a DC motor and a small electronic control unit.
The basic mechanical construction of an automatic door has been depicted in figure.
A suitable length of wire made with stranded nylon is attached to the left as well as right hand sides of the door and strung across four nylon roller guides – this structure can be easily understood from the given figure.
The wire is attached to the spindle of a DC motor. It’s rotational direction is dependent on polarity.
Such motors are found in many model building shops or from electrical equipment suppliers. They must be suitable for operation from 6 to 18 V.
It is enough to loop the nylon wire around the motor spindle a couple of times. Correct tension is gained by introducing a tensile spring in the wire, this is shown in the above figure.
A small push button switch is installed in the frames of left and right hand door. The push button ensures that a switch contact is closed, when the door is completely open or closed.
One might need a light barrier or similar device that can transmit a positive pulse of suitable length when a person is approaching near the door.
As shown in the sliding door circuit diagram above, it consists of a bridge circuit which contains transistor T1 to T4, depending on the logic level at the bases of T1 with T3 or T2 with T4, it can determine whether the motor is standstill, clockwise rotating, or rotates anti-clockwise.
The motor can be replaced by D1 and D2 (with limiting resistors R8 and R9 respectively), when a person is testing the circuit.
The choice of the transistors is dependent on the current that the motor is drawing. The current must not cross a limit of 500 mA. T1 with T3 and T2 with T4 form pair that are complimentary, for example BD239 with BD240.
A shot pulse at pin 6 of bistable FF! sets the door in motion: however, it may be needed to reserve the connections to the motor for the first time. It touches switch S2 when the door is fully open.
It is insignificant whether it is just a touch or the door is keeping the switch depressed.
The motor stands still for a very short time, this is adjustable with P1; and then it rotates in the opposite direction, enabling the door to close. If, when the door is closing, the light barrier is actuated the motor changes its direction again and the operation itself gets repeated.
Switch S1 provides a pulse when the door is closed. It causes the motor to get turned off until the next time the light barrier is being actuated.