MacGregorSailors.com

Nice drawings. I typically use Excel for that kind of stuff. Back when I actually worked as an engineer, we could actually get live prduction data into Excel, and with some simple graphics, I could get usable live data to people who had no business messing with the real control system.

Typically, a diode allows current flow in one direction, but prevents current flow in the other. As such, they are often wired inline (cut a single wire and connect the diode between the two pieces).

Ok, WITHOUT HAVING READ THROUGH THE WHOLE THING (all the links, etc.), You mentioned limiting voltage. That suggests a zener diode. They are useful for capping a voltage. But, they are typically wired accross a source ( connected between two wires). What they actually do is described in more detail here.

Obviously, none of that jives with the diagrams. So, the diode you show in option #1 may very well just be there to prevent a voltage being forced back onto the transmit pin of your NMEA cable. Whatever it plugs into may well be sensitive to such things. Bottom line, it costs money to embed diodes in a cable. Thus, the manufacturer didn't do it without a reason...

Of course, I notice that the NMEA cable is not in your second diagram, so maybe this is not an issue at all...

The more I read it sounds like it is some combination of a type of a diode and a resistor to cap voltage levels for certain sensitive receivers you might hook the GPS to.

You are correct that the second drawing does not show the Lowrance NMEA cable. This is my interpretation of how the connections could be made if you don't have the extra NMEA cable. From a physical connection standpoint it will work, but it may have electronics issues. As I say, it is not the way the Mfg does it and because it does not have the resistor / diode in line it may cause problems.

USE DIAGRAM #2 AT YOUR OWN RISK.

I do however think in most cases it would work. In the link to the wiring document for the different Lowrance GPS where they detail the connections to a VHF they even mention needing to cut off the resistor / diode in some cases.

Duane Dunn, Allegro wrote:You are correct that the second drawing does not show the Lowrance NMEA cable. This is my interpretation of how the connections could be made if you don't have the extra NMEA cable. From a physical connection standpoint it will work, but it may have electronics issues. As I say, it is not the way the Mfg does it and because it does not have the resistor / diode in line it may cause problems.

USE DIAGRAM #2 AT YOUR OWN RISK.

I do however think in most cases it would work. In the link to the wiring document for the different Lowrance GPS where they detail the connections to a VHF they even mention needing to cut off the resistor / diode in some cases.

this is very interesting...
so what i hear you saying is that not only do i NOT need the LEI-Extras.com NMEA 183 cable, but even if i had the cable I would be instructed by my VHF to cut the resistor/diode.

huh...

i still gotta understand how to set-up once all the connections are made. that is a bit confusing for me.

Bobby T.-26X #4767 wrote:

Duane Dunn, Allegro wrote:You are correct that the second drawing does not show the Lowrance NMEA cable. This is my interpretation of how the connections could be made if you don't have the extra NMEA cable. From a physical connection standpoint it will work, but it may have electronics issues. As I say, it is not the way the Mfg does it and because it does not have the resistor / diode in line it may cause problems.

USE DIAGRAM #2 AT YOUR OWN RISK.

I do however think in most cases it would work. In the link to the wiring document for the different Lowrance GPS where they detail the connections to a VHF they even mention needing to cut off the resistor / diode in some cases.

this is very interesting...
so what i hear you saying is that not only do i NOT need the LEI-Extras.com NMEA 183 cable, but even if i had the cable I would be instructed by my VHF to cut the resistor/diode.

huh...

i still gotta understand how to set-up once all the connections are made. that is a bit confusing for me.

Its confusing to me also.

Let's see if I can clear things up.

In this Lowrance document,

http://www.lowrance.com/Manuals/Files/M ... 4_add1.pdf

which is for a different GPS model, but the only one I can find with any reference to the NMEA cable with the additional diode / resistor that is on the NDC-4 cable, they say

Some VHF radios, such as the popular Uniden brand, have input levels
which require use of an additional diode and resistor built into the
M68i data cable. This is Wiring Diagram A, which is described on
page 2. The majority of the DSC radios will work with the resistor and
diode as provided by Lowrance Electronics.

A few other radio brands (and other electronic devices) that meet the
NMEA 0183 standard won't need these adapters and you will have to
remove the resistor and diode to make those work. This is Wiring Diagram
B, which is described on page 3.

Consult your other device's owner’s manual, then read through all of
the following instructions before you begin. Use the installation diagram most suited to your brand of radio or other device. If your device
manual indicates an RS-232 connection (i.e., a computer), remove the
resistor and diode and connect using Wiring Diagram B. Most other
connection types (TTL; NMEA + and NMEA –; differential) will require
Wiring Diagram A.

I suggest you read the Lowrance document and the manual for your VHF or device, and make your own decision. While it is for a M68i GPS the cable looks to be identical to the NDC-4 cable sold for the Eagle SeaChamp 2000C DF and I think all the same electrical requirements apply.

If you go to LEI-Extras.com and look up the cable needed for the M68 NMEA connection it is the NDC-4. I just confirmed this.

The safest choice is to get the NDC-4 cable and connect up the wires as I described in diagram #1. This is what I did. If it turns out that it doesn't work for you, the next step would be to cut off the diode / resistor as they describe and try it that way. I would cut everything in a way that left enough wire length that I could put it back together if I needed to. If after cutting off the diode / resistor it works then in reality you did not need to buy the NDC-4 cable at all and could have used wiring diagram #2 I posted. But what the heck, better safe than sorry.

Now if you know more about electrionics than me, and your radio or device documentation gives you enough details that you are sure it is what Lowrance calls a "true RS-232" device you can just go straight to diagram #2 and skip buying the cable. However don't call me if you see smoke. I don't know what, if any, damage might result from hooking it up directly to a device that needs the diode / resistor.

I think I could have done this with my autopilot. It was previously hooked up to a cable from my old Lowrance GPS which did not have a diode / resistor (at least not visible externally) and it worked fine.

Now the real question is for some of you double E's out there to determine what the correct diode / resistor combination is so we can just go to radio shack and buy the components to put between the VHF wire and the yellow wire. This would let you avoid buying the NDC-4 cable when all you really need is a couple $1 parts to splice into the existing speed sensor cable.

Perhaps information in this document will help

http://vancouver-webpages.com/peter/nmeafaq.txt

The NMEA-0180 and 0182 standards say that the talker output may
be RS-232, or from a TTL buffer, capable of delivering 10 mA at
4 V. A sample circuit shows an open collector TTL buffer with a
680 ohm resistor to +12 V, and a diode to prevent the output
voltage from rising above +5.7 V.

NMEA-0183 accepts this, but recommends that the talker output
comply with EIA-422. This is a differential system, having two
signal lines, A and B. The voltages on the "A" line correspond
to those on the older TTL single wire, while the "B" voltages
are reversed (while "A" is at +5, "B" is at ground, and vice
versa)

In either case, the recommended receive circuit uses an
opto-isolator with suitable protection circuitry. The input
should be isolated from the receiver's ground.

In practice, the single wire, or the EIA-422 "A" wire may be
directly connected to a computer's RS-232 input.

Can anyone spec part numbers from this?

You do get a voltage drop of 0.5-1 volts off a forward biased diode.

So, if that's all you need to be compatible, then ok that works.

In fact, I've done that for a cigarette lighter adapter that put out just over 5 volts, when I wanted only 4.5...

A sample circuit shows an open collector TTL buffer with a
680 ohm resistor to +12 V, and a diode to prevent the output
voltage from rising above +5.7 V.

This sounds like a Zener diode setup, which would be across two wires and therefore not like what your diagrams show...

However, zooming way into the pictures from that first link does look like the diode is across the two wires (rather than inline with one) with the resistor inline with the yellow. Look closely at the heat shrink...

So, it looks like a standard Zener Limiter circuit, which is shown and explained here.

Well, you have the specs on the resister, and this ought to work. You also have the specs on the diode, namely a zener diode with a reverse break down at about 5v, such as this. It looks like we're takling about a really low current. I think 10ma was mentioned somewhere. Well, 100ma (10 times the spec) times 5v = ~1/2 watt, which is what that resistor is rated at and twice the diode's rating...

With that said, no I'm not taking responsibilty for you letting the smoke out of your toys either... But, just telling you what the documentation/information says to me...

A final word of caution: Make sure you get the polarity on the diode (and resistor ) right...

My putting the diode inline on the yellow was purely a guess at what was under the black shrink wrap on my NDC-4 cable.

I'm sure your understanding of the circuit is much more correct than mine. I'll revise the drawings.

Well we're back from 4 days out on the Sound. All systems worked great as connected in wiring diagram #1. The GPS / Sounder, speed through water sensor and autopilot connection all were given a full workout.

I did find I needed to tune the speed through water sensor. While we were in the calm lake on the way out I matched the speed through water to the indicated speed over ground. It needed a 5% boost. It's really nice to have both speed measures. At one point on the way home yesterday we were northbound in Agate Pass. The speed through water indicated 7.0 knots while we were seeing 10.2 knots over the ground. The current popup on my chart predicted a 3.4 knot northbound current. Being able to see the speed differences, both for and against you, gives you another level of understanding of what is happening around you.

The SeaChamp also did a great job of driving the autopilot. It seems to be even more accurate when following a course that my old Lowrance was. Perhaps it has better cross track error calculations. Going west on Friday the Sound was dead calm and as we left the locks I powered up to 13 knots and engaged the autopilot. It laid a perfectly straight track line right over the route line on the chartplotter. The GPS drove all the way across and in through Agate Pass doing a great job of connecting the dots.

It even handled the sloppy conditions in Port Orchard yesterday as we left Brownsville headed home. The wind was 20+ and the seas were 2'-3' from the starboard stern quarter. I did have to go to hand steering once we left the protection of Bainbridge Island on our way east.

It was big wave ROUGH, small craft advisories were posted, but heck, the Mac is a BIG boat right? The wind was 30 knots gusting to to 40 from the south. Seas were 4'-6' with breaking tops and packed very close together. We had ballast full and still had to slow to 5 knots to keep the boat in the water. I drove a looping course to let us cross the waves at about a 50 degree angle. The boat did a better job of slicing through rather than smashing at this angle. Even so the bow spent plenty of time buried in the wave faces and the spray was constant. Every 2nd or 3rd wave launched huged amounts of water onto the front dodger window and the starboard side canvas. I don't see how we could have made that crossing without a full enclosure. With it, we were dry and comfy as we crossed the 5 Nautical miles of open water. In 6 years these were the biggest seas I've driven the boat through. The X took them in stride and saw us safely back across.

I finally have all the bits and pieces for my GPS system Eagle 2000,EGC antenna, Uniden Oceanus VHS with antenna.It took a while to get the EGC antenna I ordered it Jan 19 07, from Marinedeal they came through in the end. Now all I need is for some of the 2 feet of snow in the yard to go and get some warm weather here to try to install it all. Unless one of you electronic whizz kids to come to install it for me. Next job is to get a house battery and switch. I,ll have plenty to do when the weather warms up.

Ok

Thought I should pop this up again. The Eagle SeaChamp 2000c df unit that was being sold for 499 without the GPS antenna is indeed the same unit that Duane brought to everyones attention. I think someone was thinking it was a different unit, but no, it is the same. Once you add the antenna, you are good to go.

Duane
I believe you mentioned an issue with the unit loosing the bottom over a certain depth. Did you try going into the sonar setup and telling the unit you only had a 50 kHz? I know it is SUPPOSED to know that we have the 50/200 transducer, but if you are having issues, maybe that would solve the loosing the bottom problem.

I have purchased the cigarette lighter adapter so that I could use the unit on the road as well as the water. Very glad I did. I also bought the Map Create Canada topo 6.3 so that I could put Canada on the map, so to speak. I picked up a ram mount for the pedestal, a suction cup one for the vehicles, and …… you’re gonna find this hard to believe, but I picked up a handlebar mount for my motorcycle also. That’s right, I am planning on using that big box on the bike.

I have been driving all over Ontario testing the unit for accuracy and ease of use. Overall, I am very impressed. Plan routes, plot waypoints, calc ETA, not to mention always knowing EXACTLY where you are. I get an average of 10m position error with the puck sitting on the dash.

The neatest thing I find with the MapCreate add on is that at anytime you can push the WPT button, hit POI ie point of interest, this long list pops up with the following:
-airports, auto parts/service, banks, bars/nightclubs, entertainment, fishing/hunting, food stores, gasoline, government, hardware, libraries, lodging, marine services, medical service, museums/zoos, postal service, restaurants, RV parks/services, shopping, sporting goods/wear, sports, tours, transportation, universities/schools…….
Hit the thing you are looking for, then it sorts by name or nearest to your position, I hit nearest, another list pops up showing what’s available, how far, and what it’s bearing is. Hit anything on that list, it gives you the address, phone, zip postal code lat/long and asks you to choose GO TO WAYPOINT or FIND ON MAP. I find this VERY COOL!!

I have always been exceedingly bad at ASKING for directions, and now, I will never have to.

In the summer months my wife and I have always loved going for long rides into the countryside. We come to an intersection or a T in the road, we just kinda go wherever feels right. I can’t wait to try this unit out on the bike. The possibilities seem endless.

Of course, with any GPS, its reliability depends greatly on the date of the information contained in its database.

Cheers

G

You can run both transducers at the same time in side by side fishfinder windows. I had it running this way as we crossed deep parts of Puget Sound a few weeks back. Both the 200kHz and the 50 kHz tranducers lost the bottom when it went deeper than 200'. I messed with sensitivity and all the other settings on the 50kHz and could not get it to re-aquire the bottom. Then we got to Agate Pass and the water got shallow so the testing was done. I never got back to it on the rest of the 4 days out and on the way back across I was focused on the 5'-6' waves and the 30+ knot winds rather than what the sounder was saying.

We have the system on our Mac....often had readings at 350' or so while on Lake Powell....don't recall whether it was on 50 or 200 Hz..but thinking the latter. Haven't had the new system on Tahoe yet...but, it is over 1500' deep so we can play with it. Jack

FYI to add to the above technical stuff ,
I just purchased an Eagle SeaCharter 502C DF IGPS to use with a Cobra F75 VHF and after spending some considerable time on hold for Lowrance tech support - this is the bottom line.
The SeaCharter 502 comes standard with a dual transducer (50Hz should?? reach 1500 feet in fresh water) and the "usually optional speed sensor on a long cable". To connect the chart recorder to a VHF, the speed sensor can not be used because the cheaper eagle models do not allow for a NEMA Hub to be used and they only have the one NEMA port which the speed sensor uses. However, the upside is that if you cut the speed sensor off the end of the cable, you have a ready made NEMA cable to run to the VHF. You loose speed thru water but the GPS has speed over the water, an acceptable loss. The basic NEMA cable has at least 3 wires - a common (ground and maybe grounded shield) with a transmit and receive. For the Lowrance products the transmit is yellow - that is the wire that will "send" the data to the other device and orange the wire on which a Lowrance device will "receive" data from another device. Tech support at Lowrance did not see any reason to add a diode if the devices are NEMA compatible. If the line needs a zener to hold or clamp it to a particular voltage, the device is not NEMA compatible and if you try and steer things with a diode, well transmitting to transmitter will have no effect on the hardware or achieve the desired result nor will receiving to a receiver. Adding a properly sized capacitor to remove induced transient noise from the motor might be necessary but can be avoided by moving the wires away from all cables leading to the motor. Adding a diode will just add a line loss to the signal and likely shape it to an unacceptable saw tooth rather than square wave. I will let you know if anything changes once I do the install,
BTW, the Eagle SeaCharter 502C DF IGPS will not find satellites sitting on the dining room table inside a ranch with a cathedral ceiling and floor to ceiling glass windows on two sides. But it works OK in the driveway, haven't tried it inside the car yet

For what it is worth...
Ron

DON"T CUT THAT WIRE YET!

Actually you can have both the speed sensor and the NMEA 183 connection. Both will co-exist in the same port on the back of the Eagle units. I'me sure this is unsupported as far as tech support goes but it works just fine. I'm sure they are just quoting from a book rather than actually looking at the connection from an electrical perspective.

Here is the wiring diagram to use with the optional NDC-4 Lowrance NMEA cable I posted earlier. This is how I have mine wired and both devices work great. My autopilot is connected to the NMEA output, but this could just as easily be a VHF. You can even do both. I've found you can usually connect up to 3 NMEA receive devices without any problems.

Don't give up your speed through water. Having both speed through water and speed over ground is very useful information. It's amazing sometimes the impact currents can have on your cruising trips. It explains a lot of strange things regarding RPM vs. speed as well as fuel consumption that I couldn't see with my prior GPS unit.

Tested and working on my boat.


I also posted a un-tested wiring diagram that I think will work. It uses the current speed sensor cable for the connection. Rather than cut it off and use it for NMEA you should be able to tap into it and extract the NMEA signal while preserving the speed sensor signal as well. You will not have the voltage protection of the resistor / zenner diode but I think this is just there for rare cases anyway. Even in Lowrances documentation they make mention of cutting it off for some installations.

The yellow is the NMEA transmit in the speed sensor cable as well and this is not used by the speed sensor itself (I have it cut off and un-terminated on mine and the speed sensor works just fine). Connect your devices NMEA receive it and the NMEA ground to the common shield and the NMEA send from the GPS should work fine without interupting the function of the speed sensor.

UNTESTED - USE AT YOUR OWN RISK