Thin magnetic open/close sensor (elevator door sensor)


(Mike Thomas) #1

I’m looking for an open/close sensor to detect an elevator door being opened.

The sensor would be line-of-sight about 15’ from my ST hub, so all the metal involved in the door and door frame would not cause problems for RF.

However, I would have to mount the magnet on the face of the elevator door, and when opened the face of the door slides completely into the door frame. There is only about a 6mm gap between the elevator door and the door frame when it slides open, so I need a magnet that will fit in that gap (i.e. protrudes less than 6mm above the surface it is mounted on).

Does anyone know of an open/close sensor that comes with a magnet less than 6mm thick?

I currently don’t have any open/close sensors I can experiment with that are paired to my SmartThings hub. I have Digital Life and iSmartAlarm sensors, both of whose magnets are too thick for this application, so I can;t experiment with them.

From some reading that I have done around this forum, I expect I may also run into issues with the detector failing to detect the magnet when it is mounted to a steel door, so maybe I am tilting at windmills, but I’d like to give it a shot (if I can find a thin magnet).

Thanks … Mike


(ActionTiles.com co-founder Terry @ActionTiles; GitHub: @cosmicpuppy) #2

If the “magnet” is the only problem, then that’s easy to solve… magnets of all shapes, sizes, and strengths an materials can be found and purchased easily. Anyone will work as long as you can line it up with the right part of the Sensor.


(Dan) #3

I have taken magnets out of old dead 3.5" hard drives and attached them to my steal garage doors. These are very thin, about 2mm, and very strong. The sensors are then attached to the door frame.

Good luck!


(Mike Thomas) #4

Thanks.

I wasn’t really sure what type of store to check. Hardware? Hobby? Magnets ‘R’ Us? :grin:

Mike.


(Mike Thomas) #5

Oh, also meant to add - ultimately I will need to buy a sensor (compatible with SmartThings) as I don’t plan on repurposing the Digital Life or iSmartAlarm sensors.

It’s proving hard to find the dimensions of the magnet piece on Aeon’s or Ecolink’s websites (I haven’t looked at the other devices listed on SmartThings’ compatibility list yet), so if anyone happens to have such a sensor and could measure the depth of the magnet piece, it would be appreciated.

Thanks … Mike


(Wallace McClure) #6

Rather than a magnetic sensor, could you use a button or probe contact sensor? That is, as the door slides open it allows a contact to open?

I’m using a monoprice 10795 Z-Wave Sensor with an external magnetic sensor since you can run set of sensor wires into the monoprice sensor to trigger it. If you can find a sensor to work, you can run it into the z-wave sensor and talk to it via smartthings


(Jesse S) #7

Another option is to repurpose a water leak sensor. Effectively, these devices have two electrical terminals that fire a signal to the ST hub when they come into electrical contact. Using some electrical tape and tin foil I rigged up a shoe cabinet that didn’t have good clearance for a conventional open/close sensor. Details with pictures are here:


#8

The brush heads in those ultrasonic toothbrushes actually have 2 small magnets mounted at the end. They are very strong. I increased the sensing distance by almost double on my multi sensors.

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#9

Coming in late here, but the metal of the door will be a problem overtime. Not because of getting signal through to the hub which is 15 feet away, but rather because the metal surrounding the sensor will become magnetized itself over time and this will confuse the sensor into thinking that it is closed when it is not.

You probably did this experiment in science class in elementary school at one point, where a piece of metal which is not originally a magnet becomes magnetized after prolonged contact with a magnet.

The same thing happens with open/close sensors which are mounted on metal if the sensor is normally in the closed position.

See the following thread:


#10

As far as where to buy magnets, usually you get them at either scientific school supply retailers or at hardware stores. Amazon has many.

One form that I like a lot are magnetic cabinet latches. These are the kind that are used on Danish modern furniture. Typically about 5 mm thick. These are very sturdy and hold up over time. You can also get extremely thin magnets out of flexible rollup sheets, but in my experience they don’t hold up as well and are not as strongly magnetic.

The following is just one example of a strong cabinet latch. Of course these might be too strong for some uses. Sometimes you just have to experiment.


#11

In case it hasn’t been quite clear from what was posted so far, the magnet piece for a reed sensor is literally just that – – a magnet stuck into a matching plastic case for the sensor piece.

Consequently, you can substitute any magnet at all with this type of sensor. There’s nothing special about the magnet side of it other then the cosmetic appearance. So you don’t really need to have the measurements of the magnet pieces for different sensors, you’ll be able to substitute your own magnet as desired. That’s part of what different people have been talking about as they describe which magnets they used. There’s nothing special about the size of the magnet relative to any one of these sensors again, except for aesthetics. As Long as the magnet is strong enough to make the metal reed inside the sensor case move, it will work regardless of the size or shape of the magnet.


(Mike Thomas) #12

I ended up using one “rare earth magnet” from Harbor Freight (http://www.harborfreight.com/quickview/index/index/id/2125/) and mounting it on a double thickness of double-sided tape. I made sure there was a large overlap (the tape is 1" square and the magnet diameter is 5/16". Time will tell whether it will magnetize the door or not.

I chose the SmartThings multipurpose sensor. Worst case if open/close stops working, I still will know the temperature by my elevator door :grin:

Good point on the sonic toothbrush head. next time I replace one I should grab the magnets out of it.


(Charlie Morris) #13

I’m a hard disk drive engineer. The neodymium magnets are among the strongest per unit volume