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What the World
Needs Now --
Garage Door CloserApril
26, 2011
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Previous Issues |
| 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. |
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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. |
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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 |
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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. |
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Garage Door Opener |
Garage Door Opener |
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