| Author | Message | ||
     Ted Lavino Moderator Username: tlavino Post Number: 85 Registered: 01-2006 |
Don't want to spoil David's surprises next week, but perhaps a few words might tide folks over until then. The GPS sends information to the chartplotter using NMEA 0183 formatted communication. In terms of format, as we saw last night, this information is in the form of text sentences. There are also lower level protocols involved in terms of how the GPS actually connects to the chart plotter (cabling, signals on that cabling, etc.). The NMEA standard calls for a lower level hardware/software protocol that works with the nine and (older 25 pin) serial ports common on most older personal computers that conform to the RS-232 standard. The issue is that newer personal computers have done away with those type of serial ports and use a newer type of serial port based on the Universal Serial Bus (USB) standard. The problem is that the chartploter software expects to talk to the older type of serial port (RS-232) and doesn't know how to talk to the newer type (USB). The answer is a bit of software magic that makes the newer USB serial port look like the older RS-232 serial port that the chartplotter can then talk to. Many GPS manufacturers (Garmin included) have a single connection for both data communications and power input. You can purchase different cables from Garmin that plug into this port. One has a 9 pin plug that connects to an RS-232 serial port for data communications. The another has this 9 pin plug and additionally on a second cable a plug that connects to a cigarette lighter to provide power to the GPS, which is what I think you were referring to. Hope this tides you over until next week... | ||
| David Sheriff Board Administrator Username: admin Post Number: 239 Registered: 01-2004 |
Inter-device communications will be part of session 4 on Sept 18. In the meantime, checking out the definitions passed out in session 3 will be helpful. | ||
| Mark Howe Moderator Username: unclemark Post Number: 399 Registered: 08-2003 |
I note all of this was entered post class last week. I am hoping you guys will explain tonight. I am still baffled with the "EIA RS-422/ 232C" and "9 pin RS-232 compatible cabling and signals". I have a feeling that is what you were addressing with the use of the cigarette lighter connection. | ||
| David Sheriff Board Administrator Username: admin Post Number: 234 Registered: 01-2004 |
I just ordered one too. | ||
| Ted Lavino Moderator Username: tlavino Post Number: 79 Registered: 01-2006 |
Greetings folks, I've received the GlobalSat BU353, and it appears to work great. It comes bundled with software by Prolific that allows the GPS connnected to the USB serial port to appear to be connected to an RS-232 serial port. VNS, Coastal Explorer and ChartView all were successful in communicating with it using the software RS-232 port. The unit is WAAS capable and has a 20 channel receiver. Quite attractive to me, as I don't tend to use my GPS in chart plotter mode, preferring to use the bigger screen and increased functionality chartplotter software loaded on my laptop, and only us the GPS to update position information. This unit allows me to do away with a fairly bulky GPS, external antenna (my Garmin GPSMap 76 seems have fairly low sensitivity, something I'm told later models don't share) and GPS power cable (the USB port powers the GlobalSat unit). If interested you can get it delivered for under $40: http://www.buygpsnow.com/bu-353-353-bu-globalsat-gps-mouse-water-proof-receiver- sirf-stariii-usb-gps-water-bu-353-waas-455.aspx | ||
| David Sheriff Board Administrator Username: admin Post Number: 226 Registered: 01-2004 |
Thanks for the clarification, Ted. I'm following you, I think. The trick is to make a USB port look like a serial port to the software. Which does not seem difficult. Adapters shamapters. I have no idea whether Coastal Explorer accepts NMEA 0183 sentences through USB. I do know it accepts the AIS receiver through a serial-to-USB converter which did come with a driver disk. I know better than to extrapolate that experience into any kind of conclusion. To increase the confusion level, the Garmin GPS76Cx units, for which I have elsewhere expressed a growing fondness, only come with a USB connection. I have updated software through them, but not tried to connect them to a navigation program. I eagerly await the results of your GPS-on-a-chip interface experiment. My most recent interface triumph was getting an intelligible signal out of a 0183 fluxgate that has been sitting around here for years. Sucker works. Look at the readings to see the cute gif animation of it's core. | ||
| Ted Lavino Moderator Username: tlavino Post Number: 77 Registered: 01-2006 |
In an earlier post I suggested those looking at using one of the GPS-on-a-chip models such as the Garmin GPS 18 or any of the newer models based on the SiRFstarIII chipset such as the Globalsat BU353 tread carefully. My reasoning behind such a statement comes from the fact that many navigation applications support NMEA 0183 protocols only, which specify an RS-422 interface. In practice, GPS hardware that purports to support NMEA 0183 protocols will also work with RS-232 interfaces found on IBM compatible computers as well. If you followed my previous post, you will realize that the NMEA 0183 formatted sentences coming in via USB need to be presented to the navigation software as if it was coming from an RS-232 compatible serial port, essentially the second half of the journey described in the previous post, as the signals are already in USB format when they leave the GPS. The vendor of the GPS needs to bundle software that creates a software RS-232 port in your computer that the navigation application can talk to. This is the tricky part. Not all of these GPS units come with such software, and if they do not all versions of this software will work correctly, hence my suggestion to tread carefully. You may purchase a fully functional GPS, but without this software working correctly, it will not talk to your navigation application. Applications that have been modified to use USB serial connections (such as Coastal Explorer) will not have this issue to contend with and should be able to use an NMEA compatible GPS. I've ordered a GlobalSat BU 353 unit for $40. delivered on Ebay and I hope to have it by next class. We'll see how well it works with my copy of VNS and Coastal Explorer. TL | ||
| Ted Lavino Moderator Username: tlavino Post Number: 76 Registered: 01-2006 |
Agreed, I think there are a couple of related topics here that deserve clarification. First lets say you've gone out and bought a shiny new laptop, Garmin GPS 76 GPS (sorry David  ), Garmin serial interface cable, and a copy of Nobeltec's VNS chartplotting software. When you get home you discover there is not way to connect the Garmin GPS to your laptop! The serial cable from Garmin is expecting a 9 pin RS-232 serial port on your laptop. Unfortunately the laptop manufacturers have done away with them for some time now, substituting USB serial ports in their place. What to do? If you are set on using a GPS with an RS-232 serial interface, you will need to purchase an additional product to convert the 9 pin RS-232 compatible cabling and signals that the GPS can use into USB compatible cabling and signals that the laptop can use. But we're not done yet. Many, but not all chartplotter applications expect to talk to the GPS through an RS-232 interface. Nobeltec's VNS is one example that does not support USB. From what David has indicated Coastal Explorer can use either RS-232 or USB. If you are intent on using your Garmin GPS and VNS on your new laptop you need to convert the USB signal back into RS-232 format. As David has indicated you can use an RS-232 to USB converter that has two pieces. A piece of hardware that allows you to physically connect the 9 pin plug on the cable from the GPS to an RS-232 compatible serial port, and converts the signal to USB format and has a USB plug on the other side to plug into your laptop. Additionally these converters are bundled with software that creates a software "serial port" in your computer that your VNS software communicates with. It thinks its communicating with an RS-232 serial port, but it is really communicating with the USB port. So in summary the NMEA 0183 sentences exit the GPS, through its PC interface cable to an RS-232 serial port in the USB converter, where the signal is converted to USB, travels into the laptop through its USB and gets translated back to RS-232 via the software serial port and delivered to the VNS chartplotter program. If done right this works well. Unfortunately not all RS232-USB converters work well. Belken seems to be universally shunned. Keyspan's adapters have a good reputation for compatibility with chartplotter programs and are supported by all the major chartplotter software vendors. Stay tuned for part 2, which addresses the flip side: what if you want to use a GPS that supports USB serial communication with a chartplotter application that only supports RS-232 interfaces? | ||
| David Sheriff Board Administrator Username: admin Post Number: 222 Registered: 01-2004 |
Ted, maybe you can clarify this for all of us. I can buy a serial-to-USB converter and the usb port looks like a serial port to my navigation software (Rose Point). This is what you must do if you have a newer computer without serial ports, so I don't think it is unique to Rose Point. So why can't you take a GPS with a USB interface and make the computer think it is coming from a serial port? Does the device not speak 0183? More precisely, what I did was connect the GPS to the serial port of my laptop (it is that old) and run the AIS signal through a serial-to-USB converter. The software digested everything fine. Addressing the "plethora of ports required" issue, the Miltech AIS receiver has a built-in NMEA 0183 multiplexer. You can feed the GPS into the AIS receiver at 4800 baud and both signals pop out of the AIS output at a much higher rate (I think it's 19.2k) which works just fine. | ||
| Ted Lavino Moderator Username: tlavino Post Number: 74 Registered: 01-2006 |
To the folks considering the $80 50-cent-piece-sized USB GPS units (or any GPS units with USB interfaces for that matter), I would suggest treading carefully. The NMEA 0183 standard specifically calls for an EIA RS-422 interface which is fairly compatible with the EIA RS-232C standard serial ports found on many computers until recently (see my discussion with David at http://www.electricmarine.com/discus/messages/159/4992.html?1176355225). All the marine chartplotter software I've seen supports communication using EIA RS-232C serial ports only, not USB serial ports. These disk type GPS units are generally used in land mobile applications using bundled chart plotter software (actually the GPS is bundled with the software), such Microsoft Streets and Trips (http://www.microsoft.com/streets/ProductDetails.aspx?pid=001) or DeLorme (http://shop.delorme.com/OA_HTML/DELibeCCtpSctDspRte.jsp?section=10122&minisite=1 0020) that was specifically designed to interface using USB. I would love to be able to use one of those types of GPS units with my marine chartplotter software. I would be able to eliminate extra power cable, and the GPS itself is the same size as the external antenna I'm required to use with my GPSMap 76 due to poor reception from the nav desk in the salon. But the interface is not supported by the marine industry. Sigh... | ||
| David Sheriff Board Administrator Username: admin Post Number: 205 Registered: 01-2004 |
GPS has been just about reduced to a chip, certainly a small chipset. As such it is very cheap. Your cell phone has a GPS in it. The money is in the display. Tell him to buy it and try it out. I bought Rose Point charting software for class demonstration. It is very well reviewed. I don't know it very well yet, but I got a GPS connected along with an AIS two weeks ago in about an hour. I have to get to the boat this weekend and play with the new toys. I have to maintain that one class lead on all you students. Unfortunately, it does not happen to me in order. There is so much stuff to figure out I can poke anywhere I like and there is something to record or install or operate or wire up or find on the web. I do hope you guys get good at finding references on the web. Then I can concentrate on the hardware. This is pretty exciting to me. This is the first class I have ever been in where we did live internet. It really has its possibilities. We could have several people on computers looking up the answer to any question that came up. I found sufficient data online this morning and posted regarding vector and raster. That subject is done with. You cannot miss the concept once you go through the readings. | ||
| Mark Howe Moderator Username: unclemark Post Number: 394 Registered: 08-2003 |
I just had a call from a sailor; he had noticed GPS units for $17 [Globalsat] and $29 w/ $10 rebate at Fry's. He was thinking about connecting one of these cheapies to his laptop by USB cable [wire] and doing all his navigating on the laptop. I told him it sounded feasible to me. Actually it sounded very sensible to me, but I am not far enough along yet to know. [And I mentioned that he should be in this class :-) ] He said he would try it out [the price is right] and I directed him to this board to report back on what he finds. |
