Bluetooth transciever in metal box - how to expose antenna?

It would probably not work at all well, if it works at all.

Take a look at

for some ideas. You might be able to incorporate a "printed inverted F" antenna into one of the panels or overlays.

WiFi controllers per se don't speak Bluetooth. There are some chipsets which do support both WiFi and Bluetooth, but that doesn't appear to be the case for the WiFi interface in the C655 (Toshiba's page says "No Bluetooth, no antenna").

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A metal enclosure is a no-go. Otherwise most modules are complete crap anyway. My experience with using Bluetooth is that you need to write a lot of software around it to mitigate problems with lost pairings or connections which won't disengage.

No. Bluetooth is not Wifi

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Maybe Chapter 4> http://218.2.28.130/tushu/book/book46/2009875549013.pdf

noa519a&fileType=pdf

Good information. It seems that possibly a vertical antenna may be best,

something like the following which is similar to that on some walkie-talkies and routers:

It's a little expensive at $7 but this is for a $3000 test set and the Bluetooth option could easily be a $200 adder. Maybe a female SMA connector can be mounted on the panel and connect to the module with a 50 ohm coax

cable:

I might need to get a module that has an SMA connector for proper matching.

These modules are $53 each but are probably far superior to the cheap Chinese versions at about $10.

Thanks for the ideas. I'll see how the module works when I get it in a few days.

Paul

Another possibility that's only $15 (but needs a separate PCB):

Also has antenna details.

Paul

Which one?

The antenna is the wiggly gold plated line at the far end of the PCB.

(...)

Putting your hand over the keyboard would block some of the signal. If you can find an area of the box, where you can insert a plastic window, with a direct view of the wiggly gold plated antenna, you should be ok. It will be highly directional, but at least it will work on that side of the box.

You'll have to cut the trace to the wiggly gold plated antenna, and solder the very tiny coax that usually comes with Wi-Fi antennas. Or, you could just drill a hole, install a panel mount RP-SMA receptacle, and screw in a variety of available wi-fi antennas.

I've had a little in the distant past. The client failed FCC Part 15 incidental radiation and decided to metalize the inside of the plastic enclosure. Then, they were wondering why the BlueGoof range was seriously lacking. I had to scrape off enough metalization to get a

2.4Ghz signal through, but not so big a hole that it would again fail part 15. It was not fun.

No. Same frequency but radically different protocols. For example, Wi-Fi is mostly direct sequence spread spectrum, while BlueGoof is frequency hopping spread spectrum. There are some wireless boards that will do both Wi-Fi and BlueGoof, but not simultaneously.

If you have a smartphone, the BT section should be suitable for testing your laptop dongle. Just make sure you set the smartphone to be "visible" for pairing.

You'll see a BT icon in the system tray on your laptop. Right click and select something like "settings". There should be a tab for selecting a COM port.

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It's an IOGear Model GBU521

That seems to be the best option for now.

I suppose we should look into certification. Some of our test sets are used in nuclear power plants and government installations where RFI may be a problem.

I have an Archos 70 Internet Tablet which I powered up and it was found by the PC and paired, although the Archos device indicated it was not connected. I was not able to assign a COM port but I was able to send a file from the PC to the device via Bluetooth. The devices were only inches apart so it was not a good test of distance. But at least I know the dongle works. The Bluetooth module may offer itself as a COM port.

That did not seem to work, but I was able to connect and send a file.

Thanks,

Paul

You might consider creating a slot antenna in the housing. This would be a fairly narrow slot aboiut 1/2 wavelength long and driven half way along on each side (from the inside). You might need a balun for best results, but even without one it could work well. (You need some free space inside the slot as well as outside - or even better a reflecting plate spaced appropriately behind it.)

Another possibility is creating half-wave slots in the housing to let the signal out from an internal antenna. They would act as filters letting the BT signal (and harmonics) in and out. Ensure the polarisation of the slots matches the internal antenna if possible. The slot polarisation is at right angles to that of a wire antenna.

Whatever antenna you use, try to keep it as far away from other conductive materials as you can. An antenna is not just the wire or slot. It also includes the space immediately around it. If that space is occupied, the antenna will lose efficiency or bandwidth. If it is a ready- made antenna it will be detuned.

Its hard to beat a quarter-wave monopole with a good ground plane and plenty of space around it. Anything which tries to be smaller inevitably results in compromises on efficiency or bandwidth. Narrow bandwidth means more risk that production variations or environmental influences will detune the antenna giving a dramatic fall in output.

John

P E Schoen schrieb:

Hello,

I tried to connect a PC to a cell phone via Bluetooth, it did not work, even over a very short distance of some inches. I had to switch of a DECT wireless portable phone, than I could connect via Bluetooth. Bluetooth uses very low transmitter power, but DECT uses much more power and a frequency close to Bluetooth.

Bye

Slot antenna?

Regards,

Boris Mohar

Got Knock? - see: Viatrack Printed Circuit Designs (among other things)

void _-void-_ in the obvious place

You really don't need BT 4.0 for what you're doing. I use the $4/ea BT 2.0 USB dongles for various abuses of the technology.

It all depends on your construction. However, if you butcher the PCB, you have effectively ruined one of the major benefits of buying a ready to play BT module. It's pre-certified for FCC and generally does not require that you recertify the BT radio. You'll probably need to certify the rest of the instrument, but not the BT module. I suggest you make every effort to use the module without modification or find a more suitable module. Pre-certified modules will probably NOT have a removable antenna or antenna connector, so modifications to the metal case may be the only economical solution.

If the position of the PCB is not suitable for projecting through the metal case, you can use a 1/2 wave slot as a passive re-radiator. Orient the slot in exactly the same direction as the wiggly gold antenna on the PCB and it will re-radiate some of the RF both in and out. This is not as good as having the actual antenna exposed to the outside via a plastic window, but might be sufficient. I'm not sure how well this will work, but it's worth a try.

I don't know anything about nuclear power plants, but I presume they are rather security conscious and RFI/EMI sensitive. Presumably, the also look at certifications before buying instruments.

It's waiting for a password (usually 0000 or 1234).

It depends on which BT profiles are included with the device drivers and config software: Serial port emulation (SPP) profile is included with most everything except audio devices. Since the RFCOMM driver was loaded, then you should have serial port emulation installed. Check your BT settings and options again.

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Jeff Liebermann     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
Santa Cruz CA 95060 http://802.11junk.com 
Skype: JeffLiebermann     AE6KS    831-336-2558

Well, if you can put a USB socket somewhere on your test equipment, there's a $12 solution for you.

I've seen some bluetooth for PCs done as a USB cable, to a molded plastic blob that attaches outside the case, under a piece of plastic trim, with its cable snake-ing through a perforation and plugging into one of the USB headers.

The USB bluetooth for PCs is not the same as that for a slave device. I have USB implemented on the instrument PCB but it is not configured as a host. It may be possible to use USB OTG to do that, but I think it will involve a lot more than just connecting a module to the RX/TX lines of the processor. There are modules with an antenna and a cable for under $20 that should take care of the issues.

Thanks,

Paul

Just as an update, I received the Bluetooth module

in the mail on Saturday and I was able to connect it to a PIC project which reads four ADC channels and transmits the values every 5 seconds at 9600,N,8,1, which happens to be the default for the module. I had already installed the Bluetooth USB dongle on my laptop and paired it with my Archos 70 tablet and was able to send a file. It did not appear to have a COM port as a service.

The module on the datalogger was discovered and drivers were automagically installed and it showed that COM14 was available. I chose that in my TTYdemo application and it worked a charm. I was unable to block the transmission by cupping my hand around the module, and even a 7"x9" 12 gauge steel plate did not interrupt the data stream. So I think it may be enough to expose just the 1/4" x 1/2" x 1/16" PCB antenna through a slot in the panel, perhaps

protected by a small plastic piece.

I'm happily amazed at the simplicity and low cost (under $20) of implementing this technology. It may be a big selling point to be able to control and read data from the test set using a laptop computer or even a tablet device or smart phone. Maybe even make a detachable keypad with Bluetooth on both ends. This may be much more practical than my previous

idea of implementing an Ethernet and WiFi connection where the test set would appear as a web page with an HTML keypad. It's cool to be able to control the device and read data from anywhere in the world over the internet, but it's really not necessary and may present security and safety issues.

But now I need to figure out how to program the equivalent of a keypad and display on the tablet device. The Archos 70 is an Android device and I didn't have any luck making an App with the DTK and Windows emulator. Maybe it will be easier to get a Win7 tablet where the same App will work on a

laptop or hand held device, and I won't need to learn a new OS.

Thanks,

Paul

Another update :)

I have the Bluetooth module installed on a PC board in my PI-250 test set, connected to the RXD and TXD lines of a PIC18F4455, and I was able to establish communication. I received a stream of text data at 300 mSec intervals, and I was able to initiate, stop, and reset the unit by clicking the I, S, and R keys in a terminal emulator (TTY.exe) similar to Hyperterm, but using a Delphi Comm driver.

I put the unit into its aluminum enclosure, and the communication was still working. I moved my laptop computer to another room, about 20 feet away,

behind two closed doors, and although it seemed to be a little sketchy, it still worked.

So, I probably won't need any sort of exposed antenna, and probably just a small plastic-covered opening with the PCB antenna just below it, will allow reliable operation. I will need to test it in noisy environments such as

will often be encountered in normal use. There may be RFI sources such as welders, hipot testers, and circuit breaker test equipment running up to

50kA from time to time. But this Bluetooth feature is just a proposed option and will be used mostly for data collection where a miscommunication would only require resending the data. It would be more serious if the unit could be inadvertently initiated.

I'm very impressed with this technology, especially when it is available at such low cost and with such simple implementation.

Paul