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What the World Needs Now --
Garage Door Closer -
April 26, 2011
  

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Have you ever had this happen to you?  You open your garage door late in the afternoon.  Perhaps you are working on the front lawn or getting something out of the trunk of your car.  Then, the phone rings.  You rush inside to take the call.  The telephone conversation goes on and on.  You forget all about the garage door being open.  The next day, you go out to your car and discover that the garage door had been left open all night.  What is needed is a device which will automatically close the garage door after it is left open for some period of time.

There are some commercial devices available which do this sort of thing.  One system shown below contains a battery powered circuit which uses a tilt switch to detect the horizontal orientation of the garage door.  It has a timer and a RF transmitter to send a command to the opener to close the door after a period of time.  I like this kind of system but it is beyond the reach of most hobbyists if you were trying to build one yourself.  A simpler system is illustrated below.
A magnet plus reed relay combination could be used to detect the open condition of the garage door.  The magnet would be attached to the door while, the reed relay would be connected to the opener rail system.  The two would be adjusted so the magnet activates the relay when the door is fully open.

Once opened, the closed contacts of the reed relay would activate a timer.  The timer would be reset when the door is closed.  When the timer times out, a one second switch closure would be activated. 

Magnet + Reed Relay Switch  
That switch would be wired in parallel with the two wires used by the opener to close the door.  An ultra low power voltage comparator oscillator and two 74HC4040 ICs are used to generate the timer.  The jumper or a switch can be used to select a time of 30 minutes, one hour or two hours.  The circuit draws only about 2ua so a pair of AA alkaline cells would keep the unit running for many years.
Garage Door Opener Garage Door Opener
 

garage door closer designed by David Johnson

 

May 2011     Issue 17

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