How to Build a Miniature Door Detection System

What do you plan to do with this device? Can you get to it for maintenance and downloading, or is it for surreptitiously recording someone's movements, without their knowledge?

Tell us more.

"It is critical to keep it as small as possible ... " Why? Tiny doors with tiny people?

A little bigger than a bottlecap, and you would have to have a computer nearby listening but this may fit the bill:

http://www.home-technology-store.com/home-security/GE-60-688-95.aspx

If you're doing covert surveillance then I can't help you.

Most door closing events are registered with a microswitch mounted into the frame. Data loggers are your best bet for computer upload!

Did you miss this part?

It is critical to keep it as small as possible (roughly the size of a bottle cap)

The microswitch could be the required size connected to the data logger by wireless transmitter if it's required; either battery or ac wiring. But if it's stealth I wouldn't consider the normal electronics, I'd go straight to product or manufacturer for that equipment.

I didn't avoid that part I just gave the product group names that I think are most commonly selected for this application, selection is required by the installer considering that requirement.

The question is how long will you want to use it without intervention? The problem is the energy supply which should be minimal and how you can recharge the battery or if you can connect it to an usual supply.

There are different approaches possible.

Hello everyone, thanks for your rapid response.I will clarify by answering your questions and with new pieces of information.

Its purpose, as I am sure you all have quickly surmised is the collection of data on the state of a door (open/closed). Rest assured it is not for covert surveillance. Its' size requirement is serving another purpose, namely, portability. This is just a project I have going on.

You will need to be able to get to it for maintenance and downloading. It would have to be able to remain active for about 3 months, with an average of 3 opening and closing of the door per day. Chances are the opening and closing of the door will occur in quick succession.

I am afraid a datalogger, is too large and pricey for this project but thanks for the heads up.

Thanks a lot for your input guys. More than one way of accomplishing this would be great. Looking forward to more.

Of course, with enough money you could design an ASIC (application specific IC)

to sense and record the events and power it with a button battery.

On a more realistic plane, in the USA we have shops called "spy shops' that do sell this type of equipment. Not sure they have exactly what you want, but..............

Google "spy shops" and see if you get anything.

Thanks, but as hard as it may be for you to believe, it technically isn't for spying. Commercially available products are out of the question due to many reasons, including price. Although perhaps, buying one then breaking it down to see how it works may help.

'Miniature event counter' is the description you can use for finding projects or kits.

(or pulse data loggers for products)

http://search.globalspec.com/ProductFinder/FindProducts?query=event%20counter

you can use the old fashioned reed switch and magnet, which can be embedded in the door. The wires can be concealed to the reed switch behind molding, or install a radio transmitter, also concealed.

I saw these in Lilliput.. but that was decades ago.

JL Mealer
http://mealercompanies.com

Dear Dayr,

You could do this with a pair of wireless/ wired reed switch, one fixed on the door and the other on the door frame aligned one above the other.

Reed switches are of magnetic type and are quite small for your application.

http://www.reed-sensor.com/Notes/General_Reed_Switch_Theory.htm

This switch can be connected on to the digital io lines of the microcontroller and write program to read the io lines. The reed switches have to be powered external (wireless would have an inbuilt batter) For every open and close of the reed switches while opening and closing of the door generates signals that can be identified by the microcontroller and stored in its memory and the data can be read on the serial port of a PC.

You would need to search on the web for resources on choice and programming code for the microcontroller, data transfer through serial port to PC and others.

Wishing you the very best in your efforts.

Best Regards

George Kottackakathu

I don't have a true solution, but there should be plenty of energy available from the opening and closing of the door to power some form of a transmitter that would send a single pulse each time it was opened, and a different pulse each time it was closed.

Perhaps this will trigger an idea somewhere...

The request was to have memory built-in to record the events.

It could be sending the pulse either to a remote or to an internal storage/clock device.

Post 19 is pretty much describing what I had in mind.

How about a simple wired/wireless camera connected to a network or single computer. Software that comes with most webcams have a motion detector that starts recording when motion is detected. This would log the time, date and what was going on.

My phillips webcam has a built in motion detector in the software.

X10 cameras were advertised a while back to monitor over the internet

http://www.x10.com/cameras/va11a_s_mcpx_ps34.html

You can make as small as the size of standard shirt button size and thickness and install that to the part of the door which is facing each other either both are stationary or moving during opening and closing.

I am not sure why you want to do this but it is done in sensative areas we need to monitor.

Masyood

The suggestions are correct but based on a battery or any other continuous power supply. Depending on the time and number of operations the problem will be if the battery is still at right voltage when an event occurs and has to be recorded.

It is possible to generate at each operation a bit of energy which can be saved and so supply the circuit when it needs it. As you know the variation of a magnetic field induces a voltage difference in a conductor. If you use a coil with an iron core for higher field density and a PM every time the distance between them is modified a voltage appears at the coil ends. This can be used to load a capacitance and supply the record of the event in a memory. The voltage sign being related to the sign of the field derivative versus time you get also the information if the door was opened or closed. I will not go into the details and stay at the principle level which has the advantage of being always ready to recognize and record the event. If the device is on the door and the PM on the frame the usual opening velocity will generate rather high speed changes and thus high voltages. All has to be computed but I quite sure that it will work. With new PM the B values are quite high so that dimensions can be very small.

This is old technology new is based on ceramic hard magnet with myltilayer magnetic and electronic circuits

Other alternate is based on IR near radi wave technology

MAsyood

The sensing unit would be a mercury drop switch with opossed contacts, 1 for openning and 1 for closing. Innertia will activate one or the other, connect these contacts to trigger independent counters and poll the contents of the counter in BCD into a little ram along with the BDC value of a cheap watch with BCD output, you need no display and the data processing will take place away, so a couple AA batteries will last for months. The device will be the size of a fake doorknob.

Anyone with a knowledge in electronics would need no instructions on how to build it.

Yahlasit

Forgot to tell you that you need to filter the bounce of the mercury drop to allow a record only after a few seconds.

Yahlasit

Also, when I said "data processing" I meant data aquisition, because the process consists of data register, wich takes place within the portable device.

Yahlasit

Hello guys,

Thanks for all your input.

Chris and Tech-Comm, a reed switch and magnet sounds simple and hopefully cheap enough. They definitely would have to have an inbuilt battery.

Tech-Comm, with regards to data transfer to PC, are you talking about RS232/USART or something else?

Nickname, thanks for the alternative outlook. Will the system you described work if the door opens slowly and if it travels smaller distances that normal doors do?

Masyood, you say it can be roughly the size of a shirt button. That is very encouraging but could you please elaborate further on that? What are the components you are thinking about here? The more specific the better.
Also, you presented other ideas involving ceramic hard magnets and IR. Could you elaborate further or give me links about how such a system works?

Guest, thanks for yet another alternative. The mercury-based system is interesting. Do you think it is possible to miniaturize it even further?

I am grateful to you all. Looking forward to hearing more from you all.

You surely can miniaturize the sensing unit by replacing it with a linear hall sensor the size of a TO-92 transistor, use one that gives you 2.5 Vdc at zero magnetic field present and fall lower when a North is near, and goes higher when a South is near (proportionally) it'll be built into the whole gadget and the actuator would be a magnetized sheetmetal little pendulum mounted in fron of the sensor. Which swings opposed to the direction of the door movement, but you'll have to use a two op-amps to get a discrete output for each case, opening or closure.
You will need dampening to filter bouncing, like immerse the pendulum in light oil.

Yahlasit

This thing is self contained, you don't need a "counterpart"; it travels with the door and no external wiring is required, so you don't need a nearby device to process the signals.

You can come back after a week and dettach the device, connect it to your PC and start downloading all the doorness that occured during that time.

Yahlasit

Yes.

The system works if the field has a fast intensity change. With a flat magnet and pole piece the changes are the fastest. If the device is placed at the highest distance with rspect to the hinge even a small angle leads to big distances and gives the right derivative of the field. What I described is a principle which could even be applied for a patent. If you do it please mention as well my name. The basic idea is to avoid a permanent power supply since over time it presents leaks and makes the function unsafe.

Of course all has to be simulated and desighned. A "try and cut" approach will not be the right one since there are too many parameters to optimize. To give an answer to a comment the PM should in this case be of the highest coercitive force possible so it is compulsory to use PM of last generation the traditional AlNiCo are not at all for this application since for an open-close function the magnetic losses are too big.

If you need support we can discuss further on the basis of private messages.

use 8-pin pic connected to printer port. program pic to monitor switch and to tell time (lots of ways). free printer port software in circuit sites on web but computer not needed for time. pics make Killer monitoring Alarm systems 4 under 5 $ inc pcb and lots of ways to switch the door and display time

well under 3/4 sq. inch

16F675

1 or 2 resister

maybe 1 or 2 leds for monitoring

even 1 or 2 watch battery 4 power

last reply

12f 675 not 16F

Yahlasit, thank you for your thoughts. I will certainly consider it for this system.

Nickname, the system you described sounds very promising. The longevity of the system would increase dramatically. However, if pursuing it requires too much time and money, I might have to forgo it. If I do decide to take it up, rest assured I will give credit where it is due. I will certainly give it a preliminary assessment.

Guest, thank you for your valuable input.
As far as I am aware, a RTC hasn't been programmed. Am I wrong? If it needs to remain relatively accurate (to the minute) for 3 months would that change anything?

Also, in this model, won't an EEPROM be required of storage will take place over 3months? 128bytes is enough for storing state (open/close), time, date over 3 months at an average of 6 state changes per day?

Also, I would like to hear what you guys think of using IR as another alternative sensing mechanism. Please keep in mind the importance of size and cost.

Thanks a lot guys!

I don't know about the data recording side of this but Southco make latches with the micro-switch built in. I've also looked at hinges with built in switches but can't remember where.

Didn't read all the answers and don't know if this could help but my brother has a watch when he goes training on his bicycle that records heart beat, distance, date, and a whole bunch of other data. The reed switch on the wheel would probably be the part you're interested in. It comes with a software that let's you keep track of your progress (looks like outlook).

Check performance sport shops....

Perhaps a variation on a device called I button

http://www.maxim-ic.com/products/ibutton/applications/index.cfm?Action=DD&id=31

1) button and modified device can be attached to door to detect open and closed

2) button stores information

3) information can be extracted later using 1 wire application on a computer

It is smaller than a bottle cap. Can be connected directly to a computer using a 1 wire reader. It has a self contained battery (self sustaining)

Design of such a system can be yours for the low low price of 3 easy payments of $999.95. If you order now, a set of Ginsu knives will be included.

What you describe is a RFID system wit carry on recorder. The button is totally passive and cannot recognize a door status and save it. It is a control for the walking man not for the place.

"The button is totally passive ..."

Not entirely true - the Maxim site lists iButtons used as dataloggers. Unfortunately, the only logging versions they list at present can only log temperature or humidity.

Thus the "variation" on the concept.

The "walking man" portion (wand, device) as part of the door monitor system.

Button on door, wand on say...door jamb.

Thanks for the info guys!

Maybe you could use this as part of your design. Sorry but I don't know what you would do about the telemetry part.

http://www.euchner-usa.com/Hinge_ESH.asp