Serial connections to laptop

[cnh]

I have been reading the posts about connecting serial ports to GPS and Navtex, and would like to pose a question.

The GPS and Navtext [I have the NASA PC version] are behind a panel. I would like to fit sockets in the panel so I can connect from there to the laptop.

It appears that of the 11(?) pins on the serial port, you only need 3: ground, NMEA in and NMEA out. I had thought of using a stereo jack socket and plug [2.5 or 3.5mm] and wiring the 3 connections to that. The socket would be a lot easier to put into the panel than a serial port connector.

Any thoughts as to whether this would work?

Nicholas Hill

Channel Pilot

 

[RichardTaylor]

I assume you have a 9 pin "D" serial connection. I would be concerned about using a jack plug to connect in case you short circuit when inserting the plug.

2 options I would consider is

1) A 9 pin D plug - advantage is you can use a standard 9 pin lead from the lap top to the socket.

2) A (5 pin) DIN plug - you would need to make up both the socket and the lead from Laptop to DIN plug.

All should e available from Maplins and the like.

HTH

 

[Talbot]

I fitted a telephone socket - I purchased a complete extension kit from maplin, then joined the phone plug in to the serial lead - worked a treat until the robbin barstewards knicked the lot when I was done over.

 

[cnh]

Thanks, PaxiMoon: you say there's a danger of shorting the connections with a jack socket. That hadn't occurred to me.

What I'm really after is a circular connector - and a DIN plug sounds a good idea - so that I don't have to do any fancy carpentry. The panel is good thick wood, and it would be either question of simply drilling a hole for a circular connector, or getting a proper woodworker in. My skills are not that high in that area!

 

[pappaecho]

I have no idea how NMea in and out relate to normal serial communication, via a software protocol, like Xon- Xoff. If the baud rate is low and the data stream short, then it is possible that no protocols are used at all.
If that is the case, then the 9 Pins D plug has pins 2,3 and & which are relevant. Pin 2 is transmit data, pin 3 is Receive data, and Pin 7 is signal ground, eg. the reference point.
You can then try connecting NMea in to pin 3, Nmea out to pin 2 and the remaining wire to pin 7.
I have certainly seen current loop connections done via simple mini jack plugs, so it might be worth a try using the best quality gold plated ones, used bizarrely for in car stereo systems, used rated at about 10 million watts!

 

[pappaecho]

Correction : Pin 7 is 25 way D Plug, Pin 5 is 9 Way serial

 

[fluffc]

You are correct, only 3 pins are needed.

Using a stereo plug (3.5mm) is absolutely fine - you don't need to worry about 'temporarily' shorting out the wrong pins.

I would suggest though that a 3.5mm plug/socket is a bit too fragile in the longer term; the contact area is quite small.

Likewise, DIN plugs are better but still not great.

Personally I'd suggest a round connector from Bulgin (they've got a website somewhere and their parts are available on line) but that is expensive. An alternative would be to use a 3-Pin 'XLR' connector. These are normally found in the audio industry, but are quite robust. You can also get little dust caps for the panel mounted part. See rswww.com, www.canford.co.uk, or www.studiospares.com.

Happy hunting

 

[cnh]

Those Bulgin connectors look good. I'll have a scout round at the boat show. Thanks.

 

[Guest]

Re: Serial connections to laptop ..... easy ...

As Talbot and I discussed many moons ago ... and I have posted piccies of .....

I used a standard screw terminal telephone socket / cable kit ..... as you already have deduced ... there are only 3 connections needed ... and if you pick right connections in tel. socket ..... you can even extend with standard tel cable plugs etc.

It works .... (I even had the 12v power via the socket .... )

Here's piccies again :

Tip : Excellent serial connectors and cables are old serial mouse ..... cut of the mouse .... keep the cable. If you are like my office / place - I've got loads of old serial mouse' left over from old machines .....
Paper clip opened out ..... Meter set to ohms .... soon finds which wire goes to which pin ....
Another tip ..... screw terminal blocks are good enough to join wires ... also allows adding in extras later ....

 

[Glyka]

Re: Serial connections to laptop ..... easy ...

[ QUOTE ]
(I even had the 12v power via the socket .... )


[/ QUOTE ]
Does your insurance company know this?
The first picture that apparently shows it is very frightening...

 

[Guest]

You surely are pulling my leg ???

What a ridiculous reply. Sorry to be blunt - but from that photo - you have no idea .....

The installation is safe and I would have no concerns about any Ins. Co. inspecting it .... and not only that - it always went through a fused supply ....

But of course I assume we have another Forum Expert again.

Sad isn't it .....

Have you ever thought the voltage across a standard telephone line ????

 

[Glyka]

Re: You surely are pulling my leg ???

Sorry, I didn't know you're a company owner/director. I should have known that you always know what is the right thing to do.

I am a mere electrical engineer that is always confused about Volts, Amperes and the likes.

Sorry again.

 

[BlueSkyNick]

Re: You surely are pulling my leg ???

/forums/images/graemlins/smile.gif /forums/images/graemlins/smile.gif nicely put!

 

[qetoo]

Re: You surely are pulling my leg ???

I believe it should be pins 2, 3, and 5.
I show my connection at:

http://carlten.tripod.com/Navigation/navigation.html

 

[jimbouy]

Re: Serial connections to laptop ..... easy ...

[ QUOTE ]
[ QUOTE ]
(I even had the 12v power via the socket .... )


[/ QUOTE ]
Does your insurance company know this?
The first picture that apparently shows it is very frightening...

[/ QUOTE ]

Can you expand on why this looks/is dangerous so that those of us looking for a way to put together an NMEA/12v bus for various GPS devices can benefit?

Jim

 

[fluffc]

Re: Serial connections to laptop ..... easy ...

The proximity of exposed conductive parts, and lack of cable strain relief are probably what he's on about.

Don't know what the current rating is of an RJ11, but wouldn't want to take too much current through it.

 

[Glyka]

Re: Serial connections to laptop ..... easy ...

I am sure that most, if not all, of my thoughts are already known to all of you but I will repeat them for convenience.

A cable carrying signal is one thing and a cable carrying power is another.
The key factor is voltage. The lower the voltage the more current is needed for a given power need.

The photo is frightening because there is not enough insulation (if any). You can see the bare (-) cable being only only 1 mm or so from the (not insulated) crimp bearing the (+) end to the connector.

The main problems regarding electrical circuits on board are high currents (due to low voltage), corrosion and vibration.

What I am suggesting is this: Safety dictates that all power carrying cables should be mechanically connected as soldering may melt. Cable ends should be crimped and insulated using heat shrink tube. The cables should be adequately sized and fuses must have the minimum rating. Short circuited, a cheap flat telephone cable may melt before a 16A fuse blows (16 A mean 3.5kW in a domestic 220V circuit. Would you use a 0.2 mm² telephone cable on a 3 kW heater?).

On the other hand, If a cable is only carrying signals you can connect it by soldering (and covering the connection using heat shrink tube).

Trouble-free operation requires dual wall or heavy wall with sealant shrink tubes that will keep moisture away from the cable and high quality connectors. Cheap telephone connectors made for home use will soon corrode and result in poor (if any) connection. Here we have a saying that translates into something like "cheap meat ends up being eaten by the dogs". So, maybe a marine grade, high quality, special purpose connector is not a waste of money (IMHO).

All of the above may look hysterical but these were the first things I did when I bought Glyka and never felt sorry about that (so far /forums/images/graemlins/smile.gif).

 

[Guest]

The stupid post .... what is 12v ... what is not ?

The Magellan data / power cable is a sad affair ... with neg as a shield braid around the outside of all other wires in the lead. It is supplied as a loose end item. When you attach anything to it - you find it is fragile.

The screw terminal tel socket has a number of vacant terminals not used in the nmea set-up and provide excellent way to connect the 12v supply direct to the power part of the Magellan Lead ... There is no possibility of "jump / short" to the nmea side unless something really daft happens. In fact you have more chance of short with the Magellan cable itself. I even went as far as to add insulation to make it better. The Magellan cable is fragile to say the least ... and doesn't suffer too much moving around. This system allowed the Magellan lead to be near fixed and then moving cable to be the tel cable able to take much more abuse ....

Glyka ... I applaud your knowledge as an electrical boffin .... but a little more care in studying the photo maybe ?? and also maybe asking a few questions before casting a poor judgement.

I shall ignore the Company Owner comment for what it's worth !! /forums/images/graemlins/grin.gif

The set-up has been also added to to provide interconnection of eTrex and other such as PDA etc. I am able to run a lot of things from this base piece ... albeit all items except the Magellan with separate 12v supply.

I'm still amazed that such a simple safe set-up that get's around many limitations is scorned .... not my problem ... it works and I'm happy .... you makes yer choice.
(bringing in Ins. Co. cr*p ....... is that to lend credence or weight to a useless point ??)

/forums/images/graemlins/tongue.gif /forums/images/graemlins/tongue.gif /forums/images/graemlins/tongue.gif /forums/images/graemlins/tongue.gif /forums/images/graemlins/tongue.gif /forums/images/graemlins/tongue.gif

 

[Guest]

Agreed - in the right context ....

The Magellan uses mA .... and that is what is drawn from the socket .... A quick-blow very low A fuse covers it. If I was to connect anything else to it - fuse would blow long before the cable melts ....
(edit) ... I forgot ... the cable is strain relieved by the case itself "trapping" the cables when closed up ....
Really .... I'm awestruck that you know me so well to not take suitable precautions in this .....

Back to my point of tel. cables and connections .... the voltage across a tel cable is higher than I have on my set-up ... the connections are near similar in style and method ..... there are no solder joints to fail ..... QED.

 

[Glyka]

Re: Agreed - in the right context ....

You didn't get the point. The photo demonstrates a far from clean job and by no means an example to copy.

The point that this may reflect the overall setup is not of my business.

I would never judge you if you were not keen at advising people to do the same so light-hearted.

Funny to comment on Forum Experts though...