Sugestions on how to make a water resistant device with external world connection

Take a look at scuba dive computers. The more advanced of them can log data and transfer to a computer.

Mine uses IR. Others, such as Suunto, use electrical connectors.

There are also dive computers with a rechargeable battery. I have not had a chance to take a closer look at any them, though.

Is not what you want, but what is it you do want ?

There's a code for that.

Let us know.

Look up induction loops, RFID, microwave powered sensors, FM signalling on powered magnetic couplings.

Many are used for things with no contact for many reasons, such as the circuit on a large rotating shaft, that has to be powered by a carrier wave and read back a signal encoded on it.

Even power networking (networking over mains), does the same sort of signal mixing and bidirectional communication on top of a power carrier. Only difference is it is not waterproof and has physical connections :)

Maybe look at how iButtons do it:

What Paul says about induction coupling may be the way to go. It sounds like you want your enclosure to be IP68 (to what depth?) or IP69K. To achieve that you should go contact-less.

The inductive coupling can use the carrier frequency from the docking device to charge the internal battery and then modulation of the carrier by both ends of the link can pass the information. Contact-less smart cards, RFID devices and product tracking data tags do this. The docked device modulates by current demand modulation of the carrier while the docking station can use frequency of phase shift keying.

These links might help a bit.

like

device

modulates

Thank you for all the anwers. The correct code would be IP67, but IP66 would still be acceptable. I button got good implementation of what i want, but the mehcanical design for small lots productions (100 pieces) is not trivial (or it is and i am missing something here?).

One option that came to my mind would be using some isolated DC DC module with exposed terminals. The main problem is the size o the module.

Any off the shlef product that might help implementing any of the proposed solutions by Paul on a very compact way and still with a reasonable cost? The only one i know for wireless power transfer is the Texas Instruments one, but might be others. The philips one use IR for communication, that would be one possibility, but the power remains a problem.

Thank you for all the help!

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I don't think you're going to get there from here using off the shelf modules, unless you're willing to have something as big as the world's first atomic wrist watch:

I think you're pretty much doomed to doing a PC board design and working out all the bits yourself.

Nice example. But yes, i am designing a board already to deal with al the rest (its based on a MSP430). The recharging circuit it is also already embedded on the design. When i asked for an off the shelf module was just to deal with the isolated power transfer (i can implement irda with no problem). The mechanical part is being designed and will be custom made, using just a few parts of OEM wathes as the wrist band. I have a reasonable experience with the design of digital and analog circuit, but i am not an wireless guy. I have almost zero experience designin any wireless circuit. An equivalent example of what i am looking for, but related just with RF data transfer would be these modules:

With these you have to implement the whole digital part of the communication, but the RF frontend is ready and tuned.

Thank you for the help!

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You may be able to learn something from vivisecting one of these:

-- Roberto Waltman

to

Yeah, they have been doing the wireless charging of a number of devices for some time now. This is very different from data comms which is typically RF, although at very close distances you could use baseband, possibly superimposed on the power transfer. In reality this is just an air core transformer.

Rick

I think that as long as you can stand having it only communicate when it's in the dock that RF is way too complicated for your needs.

An inductive charger that "talks" should be fairly easy to implement. The charging itself would be a matter of a coil in the dock and one in the watch; feed the charging coil with AC current, turn the power on and off to the charging coil to talk to the device, and have the device short out it's pickup coil to talk back. As long as the charging coil in the dock is fed with a constant current you should be able to read off your back-talk just by looking at the voltage on the charging coil.

You might take a look at the design of the "vault" for aircraft crash data recorders (i.e. the "black boxes") to see if there are any engineering ideas there that you can use for inspiration.

The newest devices are FLASH-based, and all the the external electronics are sacrificial, except for the chips in the "vault".

After being able to recover data from the Air France crash (a year or two under the ocean at 10,000 feet or so), I'm convinced that the black box makers are doing something right.

DTA

I guess it's only fair to mention that the first and foremost thing they did right is to get themselves employed by an industry that can justify prices for such items which would drive most other customers about this close to cardiac arrest: "So let me see if I got this correctly: you are seriously trying to charge us US$ 12000 for a glorified MEMORY STICK, right? Are you completely out of your friggin' mind?"

Well, the federal government allows me the privelege of operating a little Cessna without adult assistance (i.e. I have a private pilot's license), so I have a little bit of insight into aviation prices. Here goes.

a)An ex-colleague of mine had a helicopter. The belt in the helicopter that transfers torque to the main rotor was worn, so he had to buy a new one.

He said that he looked at the belt, and imagined that at an auto parts store it would be worth about $10. But he mentally multiplied by 10 to estimate the aviation equivalent price--about $100. Sure enough, it was about $100.

The "x 10" formula is telling.

b)I'm aware that there are those in the aviation community who have discovered that certain Cessna alternators are the same part as certain automobile alternators. The Cessna price is about x3 the automotive price.

c)Aviation markups in electronics also occur because of very low production volumes. A flight recorder (and all parts thereof) are likely to be very expensive because there isn't one in every home.

Even the software in a flight data recorder is likely to be expensive because of the DO-178C requirements.

DTA

There's one point different from garden-variety parts: The aviation parts need to be traceable, so if one breaks down, the others from the same batch can be taken out of service. I have a pair of perfectly OK oli pump gears which had to be changed due to somebody losing his oil pump.

The paperwork is pretty heavy, and not free, for sure.

I really liked the idea of buiding an "air core" transformer. But seems to be expensive to implment that solution for a small production (100 units). I will take a look at my country if i can find someone that can manufacture both coils. The final circuit would be basically a flyback with an air core transformer?

Thinking about some COTs solution came up to my mind on using a very compact transformer, and use exposed pads connected to one of the transformers side. The dock would be the rest of the flyback circuit. The communication i would go for IRDA.. seems to be the most simple solution. Any idea of compact transformer i could use. The required power is ridiculous.. (20 mA to charge the battery with 5V). Mybe i coude use an Ethernet transformer..

Any sugestions?

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Airworthiness directives are a godsend, for sure. For aircraft, that is how it has to be to make it fairly safe.

But there can be awkward situations. One of the guys at the Marshall, Michigan soaring club has a model of glider (forget which one) where the tail or the wings or something like that cracked off a couple of times (all fatal accidents), and the manufacturer and the FAA aren't sure what to do about it or if anything can be done about it.

So, he has this glider that he can't use because it isn't airworthy, and nobody has a timeline for when the powers that be will decide how to address the problem or if it can't be addressed and he is the proud owner of aluminum scrap.

But those sorts of problems are rare. For most structural or control issues, they can usually put together an inspection and repair requirement to take care of the problem. Having your aircraft converted to aluminum scrap due to a problem that can't be resolved is pretty rare.

But, yeah, I support airworthiness directives and the whole monitoring process. That is the nature of airplanes. If a wheel falls off your car, you will probably survive. But if a wing falls off your airplane ... unless you happen to be flying above a mattress factory (like one of the Batman episodes), the outcome is generally unfavorable.

DTA

Way back when a British engineer named Gordon wrote a couple of good Penguin paperbacks: _Structures_ and _The Science of Strong Materials_. Struck me as really good background for someone like me who never did mechanical engineering. Such a thing was one of his topics. Safety margins in sailplane wings are built in mostly to take the stress of holding the fuselage up, less to cope with the stress of the fuselage crashing up from below. So a hard landing in a sailplane can crimp the wood in the wing spars in a way that's hard to inspect for, weakening them so they'll let go at a future date. (Probably the FAA has already thought about this.) Just a grim supposition. Put me right off aviation unless I'm paid.

Mel.

I'm not sure what pops into your mind when you see the term "air core transformer", but what I would do (and what I think people are thinking) is an assembly that looks something like this:

.--------. | .---. | |xxxx| '-' |xxxx| .---------. |xxxx| | I | |xxxx| '---------' |xxxx| .-. | '---' | '--------'

The 'xxxx' business is the windings on an outer core that can be laminated steel or ferrite or whatever, the 'I' is a commercial unshielded inductor inside of your device. When you put AC on your exterior windings, it'll induce AC on the inside. The smaller the "air gap" between the outside core and the inside inductor ("air gap" is in quotes because it's really "air and anything else non magnetic") the better the coupling.

Coils are easy to wind, so a hundred of them may be cheaper than you think.