cheaper large instrument displays - mast mount

nigelmercier said:
I've been looking at various NMEA Simulators. Most are very basic, but then I found SatGen. Might be handy to have.
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The problem with NMEA is the huge variety of messages and the lack of standardization. Just look at the list of deprecated messages, 20 pages of them...

http://www.nmea.org/Assets/100108_nmea_0183_sentences_not_recommended_for_new_designs.pdf

Another 80 pages of them here...

http://gpsd.berlios.de/NMEA.txt

It doesn't take much ROM space and it's not difficult handling them all, it will just take time to implement a large number, and I don't think you can ever be sure that you have them all covered.

Covering Seatalk on the other hand is a much smaller task.
 
c files for the fonts created and sent Angus

Couple of thoughts came to mind whilst working on the housing design in CAD

1) connections - do we go for a 3 plu approach (power, NMEA and seatalk) or a single 7 core cable coming out of the device (12v + -, NMEA + -, Seatalk + - Data) my thoughts are that the 7 core cable would be cheaper, easier, more reliable for waterproofness, the only downside is it would be slightly less flexible, although a nice long fly lead (3M) would probably fix that

2) would we need to build a NMEA amplifier to get around the 4/5 device limit on a NMEA talker if mulitple displays were installed? (assuming that some of the NMEA listeners are already in use) I could forsee a device installed in the cabin that acts as a 'hub' seatalk talker, NMEA talker and 12v in one side, NMEA amplifier and power management in the middle with 4? sets of connections to the displays, this could make it a easy plug and play experience as well as reducing wiring faults...maybe even have a battery backup in there if anyone could think of a reason for it...think of it as a NMEA and power distribution interface...longer term it might allow for other YAPP style ideas to easily integrate


any thoughts?
 
ShaunG said:
c files for the fonts created and sent Angus

Couple of thoughts came to mind whilst working on the housing design in CAD

1) connections - do we go for a 3 plu approach (power, NMEA and seatalk) or a single 7 core cable coming out of the device (12v + -, NMEA + -, Seatalk + - Data) my thoughts are that the 7 core cable would be cheaper, easier, more reliable for waterproofness, the only downside is it would be slightly less flexible, although a nice long fly lead (3M) would probably fix that

2) would we need to build a NMEA amplifier to get around the 4/5 device limit on a NMEA talker if mulitple displays were installed? (assuming that some of the NMEA listeners are already in use) I could forsee a device installed in the cabin that acts as a 'hub' seatalk talker, NMEA talker and 12v in one side, NMEA amplifier and power management in the middle with 4? sets of connections to the displays, this could make it a easy plug and play experience as well as reducing wiring faults...maybe even have a battery backup in there if anyone could think of a reason for it...think of it as a NMEA and power distribution interface...longer term it might allow for other YAPP style ideas to easily integrate


any thoughts?
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This is a thought for the future - Seatalk and NMEA are quite enough to handle at the moment, and are essential to anything that will interface with proprietary equipment.

However, there is a standard for sensors "out there", and in non-maritime uses it is becoming more prevalent. It has the advantage of having a stronger standard behind it. It is also XML based, so there is lots of standard software for parsing it and so on. The interface language is SensorML; THIS is a protocol for implementing it on Ethernet or RS232.

I am NOT suggesting that this is something to do right now; but it might be a way forward that gets over the problems of Seatalk and NMEA when the project goes beyond the single instrument being looked at at the moment.
 
Only need 5 connections

12V
Ground
NMEA A
NMEA B
Seatalk Data

The other Seatalk wires are 12V and Ground, and we have those already.

I think we should get 1 working first, and then worry about NMEA fan out later.
 
Anyone likely to be sailing within a couple of hundred miles of a magnetic pole? Just noticed that my representation of magnetic declination is a signed 8 bit variable, so the calculations will go all wrong if the declination goes greater than 128 degrees E or W. :)
 
AngusMcDoon said:
Anyone likely to be sailing within a couple of hundred miles of a magnetic pole? Just noticed that my representation of magnetic declination is a signed 8 bit variable, so the calculations will go all wrong if the declination goes greater than 128 degrees E or W. :)
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Well, it is certainly feasible for people to sail within 100 miles of the North Magnetic Pole; it is within the Canadian Archipelago, and so is accessible to adventurous sailors.

The South Magnetic Pole is trickier. It happens that the Earth's magnetic field is not as simple in the southern hemisphere, and there are TWO magnetic poles; the Dip Pole and the point to which compasses point. The former is accesible to yachts - but unlikely to be of interest to them, as it is off a rather inhospitable bit of Antarctica.
 
Too cold for me, and too many bergs...I wonder if other systems have a limitation..I have never looked (although never really checked the specs on my other instruments until this project started and my tacktick displays work down to 0 degrees Celsius but can be stored at -20, all headline specs state -20 to + 50...always a sales pitch in there somewhere :-)
 
There is another thread related to this project where the problem of cases has come up. I mentioned a Bud Industries case that I'm using for a smaller display, they might do something suitable.

Also mentioned was buttons in the case. As this is to be mast mounted, has anyone considered using IR Remote? In my case (pun) the IR is only used for the initial setup, but I thought it worth mentioning.
 
Some thoughts for you to consider:

I was wondering about the buttons - if the display is halfway up the mast, how are you planning to reach them. So, I assume they will have to be remote. Simplest is a wired remote button box, but not very elegant. For "wireless" remote you can use IR (like your video remote) or radio. IR is cheap, but relies on clear line of sight to the display, and will be impaired by rain, etc, and relatively short range. RF is a little more expensive to impliment, but simple - range and immunity to obstructions is better and co-channel interference issues shouldn't really arise in practise (and easily fixed in coding).

Contrast control. I know someone dismissed "digital potentiometers" as not coping with negative voltages - but is this really the case? There are a huge number of types available, and LCD contrast is the usually suggested application, so need to do more looking. The problem with the op-amp solution is that it needs a negative supply - which I presume you don't need for anything else. There are op-amps that require very low supply current, and provide "rail to rail" output - if you use one of these, you can run it directly from the LCD generated negative and the processor +5 (or +3.3).

Have you found some waterproof connectors yet?
 
nigelmercier said:
There is another thread related to this project where the problem of cases has come up. I mentioned a Bud Industries case that I'm using for a smaller display, they might do something suitable.

Also mentioned was buttons in the case. As this is to be mast mounted, has anyone considered using IR Remote? In my case (pun) the IR is only used for the initial setup, but I thought it worth mentioning.
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You can get small wireless transceivers for a few pounds.

http://www.ebay.co.uk/itm/2-PCS-NRF...ther_Computing_Networking&hash=item2c6534a2fc

I thought about using them, but have not done anything about it. You would have to have some means of setting an individual display's address (just once, upon installation) if you had more than one in range. Something like this would do it on the circuitboard...

http://uk.farnell.com/multicomp/mcdp03/switch-dil-3way/dp/1522004


My software at the moment uses buttons to change the displayed information to one of 3 presets as well as for setup. Buttons are also used to kick off the race timers. A small remote with a few buttons, a 9 volt battery and a transceiver would cost only a few £ to make.

This could have a further benefit of when close to a competitor in a race you could change their display to something useless like water temperature. :)
 
I was wondering about the buttons - if the display is halfway up the mast, how are you planning to reach them?
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When I used to have displays like this on my previous boat they were installed just below the gooseneck. I set them up and chose what to display on each one, and then they didn't really need touching again.

Contrast control. I know someone dismissed "digital potentiometers" as not coping with negative voltages - but is this really the case?
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The datasheet of every one I looked at limits the range they will control resistance over to be within power supply limits. A sparky I spoke to said that is the case for all of them, but I'm not an expert here, so I'm only going on what I've been told.

The problem with the op-amp solution is that it needs a negative supply - which I presume you don't need for anything else.
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I was assuming that the LCD negative voltage generator output from the LCD panel could be used as the negative supply to the op-amp. I might be wrong.

Edit: just noticed that's what you are suggesting too.
 
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AngusMcDoon said:
I was assuming that the LCD negative voltage generator output from the LCD panel could be used as the negative supply to the op-amp. I might be wrong.
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It will be OK if you're careful with your selection of op-amp. The current available on that pin of the LCD will only be low, so you need to use an op-amp with current draw in the microamp not milliamp range - that narrows the choice down a bit! The overall supply voltage available will be quite low and you probably need an op-amp that will drive close to it's negatice rail. Most of the op-amps I use are optimised for different requirements, but I know there are low current, low voltage, rail-to-rail op amps around.

I will look at the digital pots, as I'm sure there are similar applications around.
 
mikefleetwood said:
Contrast control. I know someone dismissed "digital potentiometers" as not coping with negative voltages - but is this really the case? There are a huge number of types available, and LCD contrast is the usually suggested application, so need to do more looking.
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With the LCD in the project I'm working on, I'm pretty sure the contrast is set by software. There are certainly no requirements for negative voltages. :eek:
 
nigelmercier said:
With the LCD in the project I'm working on, I'm pretty sure the contrast is set by software. There are certainly no requirements for negative voltages. :eek:
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That's the case with some of them, but not all. The LCD display discussed earlier on this thread, which is 240x128 and not too expensive, needs external voltage control for contrast. It generates the negative voltage, but the user has to control it.

http://uk.rs-online.com/web/p/lcd-displays-mono-graphic/5327221/
 
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