Garage door alert

It is a workable (and clever) plan. All you need is the switch, a 9 or 12 volt DC wall wart power supply, 1K resistor and the LED. No transistors or relays needed. Put the switch, resistor and LED in series with the DC supply, observing proper polarity.

Pay a lot of attention to how you mount and actuate the switch, so that it stands up to the repeated use.

Ed

Thanks, Ed. I see your point about no need for transistor or relay, provided I can find a limit switch with normally closed contacts. I'll start looking.

Ed

Just mount your limit switch next to the top of the door, and use the NC contacts, such that when the door is fully closed, it opens the switch. Then all you'd need is the battery (or wall-wart) and LED & its resistor.

If you want 'up', 'down', and 'in between', you'd need another switch (or full up) and some logic. :-)

Have Fun! Rich

Just look for "microswitches." MicroSwitch was the name of the original manufacturer, but, like "zipper", it has become a generic name. Most of these little switches are SPDT. A good free source is old machinery. Old copiers, VCRs and printers usually contain microswitches, but newer ones may have photosensor limit detectors instead.

You can use either normally open or normally closed contacts by wiring the circuit accordingly.

Normally open:

/ LED V+ ---o o--->|----+ | [1K] | Gnd ---------------+

Normally Closed:

+---o->o---+ | | | LED | V+ -----+---->|----+ | [1K] | Gnd ---------------+

The most important thing is the mechanical arrangement to operate the switch. You want to make sure that the switch is positively actuated in both directions, but you don't want mechanical stress placed on it. Garage door motion is not the most gentle - so you may need to mechanically buffer the switch so that it is not unduly stressed.

Ed

Thanks, Stephen. I had thought about a microswitch, but wondered about how to gently engage it. Perhaps a strip of stiff but flexible material, metal of plastic, mounted to the door?

Ed

Thanks, Ed. I had thought about a microswitch, but wondered about how to gently engage it. Perhaps a strip of stiff but flexible material, metal or , mounted to the door?

Ed

Also called 'snap switch'. Here's one suggestion:

It could be mounted so that the little roller projects just slightly beyond the contact face of the door frame. When the door shuts completely, it pushes in the little roller. You're looking at maybe 3 mm of switch arm travel, so it'll be kind of a tight fit, but hardly anything of extreme precision.

Since you'll be dealing with low voltage, there's no concern for serious insulation or shock protection.

These little guys usually last almost forever.

I have such a creature at my home, and it automatically turns on my pantry light when I open the door, and turns it off when the door's closed (like a refrigerator).

If searching on ebay, you can find snap switches more easily by filtering out the 'HO train' listings. Also search on micro switch. Sooner or later you'll see a shape that causes the mounting idea to pop into your head.

They're also pretty inexpensive, so you might wind up buying a lot of 8 or something just to get one, but that's OK -- they're cheap. Cheaper than someone walking off with your items because you left the garage door open!

Well, you can get industrial-strength limit switches - they're like a microswitch on steroids. They're like the size of your thumb, but fatter and rectangular. You can get them with either a blade or a cat-whisker. I already have a picture in my head of the switch screwed to the door header, with this leaf sticking out where when the door opens, even a little, it releases the leaf and closes the switch.

These guys have a lot of compliance built in, so as long as you hang the leaf (or catwhisker) such that the clicking range is within maybe half an inch or so of the top threshold, it should last forever.

I thought I'd do a quick google on "limit switches" with the quotes, and got "about 707,000" hits:

Have Fun! Rich

Wot's wrong with a reed switch like an alarm system would use?

These are available in N/O, N/C and change over.

The circuit would be easy and the mounting simple.

They are available at places like Bunnings. (Home Depot to you Americans)

John G.

Here's one idea:

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Thanks, John.

As I recall a "reed switch" is a magnetically activated proximity switch. I have a 1976 Jaguar which originally was fitted with an ignition triggering system that used a reed switch in a little circuit board inside the distributor. A magnet in the rotor triggered it. Jaguar later replaced it with a board that uses a Hall effect transistor. But, if the one you refer to is at HD it's probably not the same technology.

A proximity switch of some kind would work, having the advantage of no physical contact and hence not subject to damage due to getting thumped by an ill-fitting, wobbly, garage door. However, an active circuit would be required. A micro switch doesn't need an active circuit, as the other Ed points out.

Ed

"ehsjr" wrote in message news:CtyQj.3745$E77.1973@trnddc05...

I must not be thinking clearly, as I can't quite see how this would work. The free side of the hinge would be hanging vertically, perpendicular to the door, when open. It would still be hanging vertically, but parallel to the door, when closed. But unless the switch was also mounted on the door I don't see how the hinge would operate the switch.

Anyway, I looked at the door more carefully and see I may not have as much of a problem as I thought. The top edge of the door is stopped firmly by the beam forming the top of the doorway. Since it is pressed tightly against the beam when closed, if I mount the switch carefully it can't get damage. I think I'll give that a try. After all, the switch cost me only about $5.00.

Ed

Yes.

No - I think you missed the 90 degree part: ">>A cheap strap hinge that can pivot to a 90 degree angle mounted >>to the inside of the door."

The hinge makes an L when the door is closed, with the vertical leg of the L screwed to the door and the horizontal leg parallel to the floor, because of the 90 degree limit.

Great!

Ed

Got it working! To neatify things I used a small project box with a connector to the PS and another to the wire pair leading to the LED. The switch wire pair enters the box w/o connector since it is mounted close to the switch. I added a green LED on the box cover to show when there is power to the circuit. All I have to do now is to poke a hole through the wall to get the red LED into the living room. This is a little tricky since we have plaster walls, and drilling a neat 1/4" hole is virtually impossible. I think I'll drill and then insert a 1/4" steel dowell and fill around it with a hard plaster... unsanded tile grout perhaps. Then pull out the dowell and insert the LED. All that will be seen is the little red spot with black ring. This will be near a desk with other things around so attention will not be drawn to it, except when it's flashing red.

Thanks for all your help.

Ed

Just want to show off the finished project!

Thanks for all the help!

Ed

Nice! Good idea making the red LED a flashing type. The resistor you mention in your writeup is 1000 ohm or 1K - not 1000K as the writeup says..

The appearance in the living room is great - barely noticeable. Nice to see the photos of the completed project.

Ed

"ehsjr" wrote in message news:QjxSj.16744$E77.892@trnddc05...

What? You must be mistaken. Look again to see if maybe you misread it. :-)

Thanks.

Ed