Help with wiring (a bit technical)

[Colin24]

Morning all

I’m hoping some of the panel will be able to help with a wiring problem I have.
If I were on shore I’d simply go and buy an appropriate cable.
As it happens I’m stuck on a ship in transit from The Philippines to Singapore for the next five days. I thought I’d take my laptop up to the bridge and plug in one of the GPS units in order to see my position moving across the chart in a chart plotting program I have.
Hears the rub, the output from the GPS terminates in a 9 pin serial plug and my laptop only has USB ports available. No worries I naively thought I’d just cut the end off an old serial cable and do the same to a USB cable and bobs’ your uncle.

Turns out there are 9 wires coming out of the serial plug and only 4 from the USB.
Although I’m sure that some of you will already have spotted it, but I’m not one of the world’s natural technicians. /forums/images/graemlins/tongue.gif I’m still hoping that it is simply a matter of connecting the 4 wires that come from the USB plug to the appropriate 4 wires coming from the serial plug.
I have onboard a full technical workshop at my disposal, tools, equipment, in fact everything apart from the tech, who is not riding the boat for the transit.

If anyone can give basic guidance it would be much appreciated.
The wires coming out of the serial plug comprise of the following colours.

Pink
Brown
Grey
Green
Black
Blue
Yellow
Purple
Red

The USB wires are

Black
Red
White
Green

I’m hoping for an answer like, USB Green to Serial blue…etc

At the Serial end I can see the pin numbers and could easily match the colours to the pin numbers with a meter if the colours are not standard.
C’mon Nigel, this sounds right up your street, surly someone at your GPS & Nav group knows how to do this.

Colin

 

[Benbow]

You need to ask the workshop to build you a serial/usb interface! You cannot just connect the wires.

 

[Colin24]

/forums/images/graemlins/frown.gif Hmm... I was worried that there'd be more to it than a simple wiring job.

Thanks for the reply. looks like I'll just have to wait until I get to Singapore.

Colin

 

[TigaWave]

You only use two wires from the gps for data and ground, these will go to pins 3(data) 5(ground) should be numbered.
USB pin 1 +5v, 2 Data -, 3 Data +, 4 Gnd.
I cant see any problem with just connecting them, I found out which wires by trial and error initially but had it confirmed.
Search on the web and you can find these details I'm sure.
Neil

 

[Anonymous]

Are you saying that you actually managed to get RS 232 serial data to feed directly into your computer's USB port without any sort of electronic interface? Or are you saying that you think it ought to work?

 

[Benbow]

Blimey. I would be happy to be proved wrong but I am very very surprised to hear that.

Have you tried it?

Does it look like a usb device to your PC?

Not doubting you (well, just a bit) but very surprised.

 

[petercornish]

UNDER NO CIRCUMSTANCES WIRE YOUR SERIAL CABLE TO THE USB PORT.

THEY USE DIFFERENT PROTOCOLS AND SPEEDS AND YOU COULD DAMAGE YOUR COMPUTER

DO AS RECOMMENDED - BUY A SERIAL TO USB CONVERTER.

 

[TigaWave]

Ok OK...I havn't tried it with a usb socket, but cant see why there should be any problem, they are both serial devices, data is supplied on one wire, at 0 volts or 5 volts.

The only reason for the larger number of pins is for control signals which on my laptop are not used when connecting a gps.

I just took ground connected that to ground then tried the data out from GPS on each pin until the plotter lit up with the position.

Cant see why it wouldn't work with usb port as this is just +ve, gnd, data in , data out. still serial, still same voltage.

The only thing to be carefull with is the +5v power out of the usb socket (I would suggest it might not be good to connect this to ground?), but you dont need to touch this as the gps is already powered. You could also easily check the voltage of the data out of the gps with a volt meter, you can see it going from 0 to 5 ish volts as it tries to send data.

My laptop didn't object to me trying every combination of the two wires in until it fired up.

The usb socket is similar to the serial port apart from that the computer gives it an address rather than with an old RS232 the device gave an address.

If your bored on a ship it could keep you busy for a day finding out.

 

[Colin24]

/forums/images/graemlins/blush.gif Oh no, now I don’t know if there’s hope or not, But it’s only half eight. Should I give it a try or not?

Colin

 

[Gunfleet]

Just make sure you look out of the window every now and then. I have this vision of ship's trundling round the world with people doing diy on the bridge.

 

[Colin24]

What Neil is saying does make sense to me. If I were able to buy the correct cable, one end would still be connected to the serial plug I intend to take the GPS output from and on the other end there will be a USB plug going into the USB port I’m going to use. Or is there some other electrickery going on in a box between the two ends?

Colin

 

[TigaWave]

I'll give it a try and see what happens if you like....but have loads to do after 9.00....watch this space.....

 

[Colin24]

I'm watching... I'm watching

 

[alan]

Should be no problem.
Both are serial data ports.
NMEA0183 uses RS232 or RS422 : around 5v on each signal wire (RS422 +/- 5v and RS232 +5v).
USB2.0 uses around +0.5v for high speed and slightly higher for low speed.

You wont hurt anything if you only use the signal wires.
For info see: www.usb.org and search for NMEA protocol for further information.
So, no problems as far as I can see.
/forums/images/graemlins/smirk.gif
Alan.

 

[Anonymous]

[ QUOTE ]
Or is there some other electrickery going on in a box between the two ends?

[/ QUOTE ]Yes. They are not compatible. I'm not sure whether you will damage anything - maybe - but it won't work.

 

[Anonymous]

[ QUOTE ]
So, no problems as far as I can see.
/forums/images/graemlins/smirk.gif
Alan.

[/ QUOTE ]I think that anyone who boldly states that there is no problem in connecting two expensive pieces of electronic equipment together via incompatible interfaces should make it clear that they have never tried it themselves and be prepared to pay up if their advice results in damage.

It does not follow that simply because two things are said to be "5V" that it is safe to connect them together in any configuration. Suppose you connected the positive of one 12V battery to the negative of a second battery, and vice versa, do you think that this would be "no problem"? Or can you see that a massive current would flow, blowing the connecting cable violently, and probably ruin both batteries?

 

[Benbow]

I would be astounded if it worked because serial and usb use utterly different protocols. Serial is, well, serial it just sends a bunch of highs and lows which the listener intereprets with the appropriate software. USB requires constant 2-way exchange and I can't believe it is capable of listening so slowly.

Even if I am proved wrong there and it does somehow understand the data stream, there is big variation in the voltage used to define hi or lo by serial devices and I have no idea about the capacity to sink current of the two systems. So even if someone got away with it once, I would very strongly advise against trying it.

I was prepared to be amazed, but offering advice without having even tried it is irresponsible IMHO.

 

[tonyjover]

I'll second (well, third) the recommendation for a Serial/USB interface connector. They're less than a tenner and will ensure that your serial connector appears as a USB device.

They also come with a small USB driver which is installed onto the laptop.

Note that they are sensitive to which USB connector you use, so if your pc has more than one, use the same one each time to avoid confusing the driver.

Good luck,
Tone /forums/images/graemlins/smile.gif

 

[stevebirch2002]

Just to confirm, they are not compatible and I hope you are not using the bridge GPS to try it out!! Beware Singapore! As you have surmissed you will need a USB-Serial converter. This is teh reason that when I bought my last laptop I insisted it had a 9 pin serial port. Cheers and good luck in SIngapore.

 

[TigaWave]

Computers happy and gps is still happy, but the plotter programme only allows me to designate com1 or com2 as data input.

Looking at usb (contacts upper most, flat plate below, grnd is far left, +ve 5v is far right)

Tried both data terminals, with nmea giving 0 or 5.75v....no black smoke.

But maybe need to look more deeply at which port the programme is looking at? a job for a wet weekend possibly.

Thought it might be useful to know if it was possible as an alternative....this is running off hand held Garmin gps 45 on external supply.

Meanwhile its back to quotes and drawings.

Neil