#1 2011-02-24 20:36:20

Registered: 2011-02-24
Posts: 351

F26 - Electronics aboard a Frances 26

[Moved from 'Technical Advice' pages, dated 06/08/07]

Jenter is approaching 14 years of age and much of the equipment originally fitted was long overdue for renewal. This year I decided to fit some new electronic equipment, which is really quite inexpensive nowadays.

The first decision, and this could have been a mistake, was to decide on separate units rather than a dedicated laptop computer or chart plotter. We already carry a laptop on board, mainly for communication via e-mail and text messaging, and know we could not afford the battery drain to have it powered continually. Also, with separate units those not required at any one time may be left in standby, or turned off. More important, a failure of one would leave the rest working, in basic mode at least.

Why a mistake, then? Q. What is the first thing you do with lots of separate 'black boxes'? A. Connect them together, of course, so they can talk to one another!

Although you may well identify some of the items purchased, this article is not about the individual boxes at all! This article is just about connecting the equipment together in a neat, tidy, secure and seamanlike fashion.

And so I spent numerous days over several weeks, feet in the air, head deep in some locker, arm at maximum stretch trying to feed co-axial aerial cables, data cables and regular power cables from one end of the boat to the other. From the G.P.S. readout on the radio, you may surmise that its wiring was not completed until Plymouth.

Each of the four items purchased came with power and data leads; sometimes combined. The cables supplied with both the Navtex and the G.P.S. had nine individual wires each. Now, if you're sure you won't be using them all, you could just cut them off short and wrap a piece of insulating tape around them. I'm not sure that is seamanlike at all! A simple calculation established that I would have to make over SIXTY connections in the vicinity of the chart table on Jenter, if the equipment was to work to full advantage.

At the top left is the new G.P.S. This item has proved very popular with other equipment aboard Jenter. 1. Directly below, the A.I.S. needs to know where it is so it may calculate the relative position of other ships. 2. The Navtex needs to know where it is so it may automatically tune in the correct stations. 3. The radio needs to know where it is so we can be rescued when we push the red button. 4. & 5. Both our Autohelm 4000, and separately wired, Autohelm 2000 need to know the whereabouts of waypoints they may be tracking towards. 6. I want to be able to download a waypoint list and a navigation log from the G.P.S. to my laptop computer.

The information is not just one way. I like to be able to enter waypoints on my computer at home on those long winter evenings and be able to load the G.P.S. from the computer in just a few seconds. That meant a socket for each piece of equipment that I wanted to connect to my laptop.

Have you spotted my first innovation? I wish I had taken a before, as well as an after, photograph. The wiring on the left hand wall was a mess with wires all over the place and large clips more suited to a domestic ring main.

A length of mini trunking was screwed vertically to the wall and contains all the aerial and power cables. I obtained the trunking from a local electrical supplier and a 3m length of 38mm x 16mm cost £2.80. The facing surface peels off for ease of maintenance and snaps back positively into position to hide the wires and cables.

The trunking on the right was bigger; 38mm x 25mm (3m cost £3.30.) It was also modified, by cutting into the side wall to mount 4 9-pin 'D-sub' sockets (RS Components sell 5 for £9). Inside the trunking five connector strips were also firmly screwed into place, above, below and between the 'D-sub' sockets. You would not believe the number of wires inside and I'm not taking the lid off to show you; it took too long to pack them all inside!

The main message then, is to use trunking to keep those wires tidy and hide all those connections.

What follows now is for the real enthusiast. Q. Why four sockets, wouldn't one do? A. No, because with a single NMEA bus there can be only one 'Talker', but as many 'Listeners' us you wish. Each of the 4 pieces of equipment likes to be able to Talk, as well as Listen. Earlier we saw that the G.P.S. talks and, on Jenter, 6 other pieces of equipment listen.

The Navtex would also like to talk to a printer so you can print off a copy of the Inshore Forecast. The A.I.S. would like to talk to the laptop so it can pass the details of one of the targets. Even the radio would like to be able to download its radio 'log'. Yes, like a mobile 'phone it keeps a log! Hence 4 sockets, which I mean to label from the top, G.P.S., Navtex, A.I.S. and Radio.

Q. Is it easy to wire up the 9-pin 'D-sub' socket? A. Yes and no. Only three wires are really needed; a common ground, a data-in and a data-out. The NMEA interface is really a simplified version of a computer's obsolete COM socket (RS232C interface). In the early days, extra hard-wiring controlled 'hand-shaking' between components. This is no longer necessary but to disable it in your socket you need to short two pairs of pins, which means soldering to 7, out of the 9, pins and having a steady hand!

Because your modern computer won't have a physical COM socket you purchase the adapter (shown), which terminates in a USB 'A'.

Q. Is there anything else I should know. A. Yes. Some of the units have simple software included which is capable of outputting to an 'old-fashioned' serial printer directly, if you can still buy one. Anything else would require the additional purchase of software, to create an automatic log book, for example. Or you can write your own software, as I intend to do!

Want to let me know what you think or ask any questions then send your comments to me.

Peter Cosker

Thank you for your interest.






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