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Old 26-11-2006, 18:48   #1
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Special Considerations for electronics

Not sure if anyone here can help answer this, but figured worst I can get is no answer...

I'm going to be creating one or two electronic gizmo's of my own, and figured there's probably some special guidlelines I have to follow in the marine environment. I'm already aware that I'll probably have to use special wires that wont corode, and the unit would have to be sealed. Aside from that what else is there to consider? For example, is there any problem using standard components on the circuitboard? Anything else I'm missing?


Thanks, Thomas
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Old 26-11-2006, 23:15   #2
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There is no blanket answer that covers all cases. Just like designing for an office or a factory, it all comes down to the application and the environment. There are bunches of conditions that you might have in the marine environment:
- high humidity
- salt spray in the air
- immersion in sea water (boarding seas, device dropped overboard)
- mechanical shock (device falls off table, boat falls off waves)
- varying roll/pitch/yaw
- "12 V" DC power can be 10 to 16 volts and/or noisy/spikey
- AC power with poor voltage and frequency regulation (e.g. from a generator)
- AC power with non-sinusoidal waveform (e.g. from inverter)
- high ambient temperatures (inside sealed cabin in summer)
- low ambient temperatures (out on deck in the winter)
- RF noise in the environment (VHF transmission, EMI from on-board electronics)
- user error brought on by fatigue
- user has wet hands / clothing / whatever

There are probably others, but that list is all I thought of in a minute. Your question, then, is just how the environment is going to affect your application. For example, if your device has no user interaction, you probably don't need to worry about their wet jacket dripping on your device.

Standard components are fine, unless you need extended temperature range or something like that. For example, I have a box that uses a regular commercial Rabbit processor module. I think it is only rated for operation down to 0 C, but that's ok because I am unlikely to be using it outside during the winter.

b.t.w. I also built it on standard perfboard, and even though I take it in the dinghy, it has holes in the case that water could get through. I just don't let water spill on it. (If it fills up with water, I'll be very unhappy.) You can get away with compromises like that on things you build for yourself.

I've had pretty good success with consumer electronics on board -- tv/dvd, vcr, laptop computer, POTS phone, cell phone, toaster (with digital controller), battery chargers (AA/C/D). This stuff all lives in the cabin, which is heated/cooled so it is comfortable for me. I have much narrower environmental requirements than most of the electronics.
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Old 26-11-2006, 23:56   #3
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If you can hook it up to an unregulated alternater, and drag it behind the boat for a mile or two, then start using it, it is properly built Seriously, take a real consideration about how you seal the unit. Consider that the old "Chess Mate" electronic chess sets, that appeared very well sealed, when used in the middle east, showed sand inside the unit when disassembled. While sealing the unit against water incursion is necessary, consider how moisture that might get into the unit will escape.
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Old 27-11-2006, 01:06   #4
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Make sure that you use tinned wire. The normal auto wire will corrode through very quickly in damp places.
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