NMEA-0183 and RS-422 vs RS-232

[Lake-Effect]

Originally Posted by carlspackler

I really love digging into wiring like this, but I am also suspicious of the reliability of anything in a noisy electrical environment with salt air all around. In my case I was hoping to wire up a BR-355 GPS Puck to my VHF, but I would need 5 volts to power it, thus a voltage regulator,

Don't give up just quite yet

The stores abound with USB charging adaptors for cars - so that's one solution for getting regulated 5v. Besides that, I've found a ton of well-regulated, efficient switching regulators for car-chargers for now-obsolete phones for around $1 apiece in the surplus stores. And ebay has many efficient step-down regulators listed for like $1.50 each.

Also, I don't consider boats to necessarily be a severe electrical noise environment. Now - a house with the microwave running and a bunch of 12v halogen lights run by a switching power supply on a cheap dimmer... that's electrically noisy

But yes, reliability is key when on the water. Know your limitations, don't adopt a solution you have doubts about.

[carlspackler]

Any 12v circuit with an inductive device such as an alternator has the potential to create surges of current on shutdown.

I bought some transzorbs from Ebay for this purpose, but I'd rather leave all this custom work for nonessential circuits.

[goboatingnow]

Originally Posted by carlspackler

Any 12v circuit with an inductive device such as an alternator has the potential to create surges of current on shutdown.

I bought some transzorbs from Ebay for this purpose, but I'd rather leave all this custom work for nonessential circuits.

Load dumping with the typical battery banks in boats is not an issue. You are protecting something , that doesn't typically occur.

Dave

[CarinaPDX]

I agree with Lake-Effect. I use an MR-350P (USGlobalsat Corporate) for GPS input to all communications gear (DSC VHF and SSB, Pactor III modem). For the 5V power supply I have hooked up an in-line cigarette lighter socket (female end of an extension cable) to the VHF radio's circuit breaker with inline fuse. I then plug in a cheap USB adapter - only a few dollars. Then I scrounged an old USB connector to attach to the GPS power leads, and plug it into the USB charger (in turn plugged into the cigarette lighter receptacle). I have the stack held together with cable ties to prevent them coming apart. Works a charm. Spare chargers are cheap and easy to replace. I liked it so much I added this GPS system to my Furuno MFD as the primary GPS input.

Greg

[Boulter]

Originally Posted by CarinaPDX

I then plug in a cheap USB adapter - only a few dollars.Greg

Are these switching regulators? I also have a GPS that needs to be wed to the VHF. If they are just linear regulators, I should have a few dozen 7805s and the like kicking around.

Boulter

[CarinaPDX]

They have DC-DC converter ICs - I have no idea what technology is inside. Doesn't matter. The output is a very precise and stable 5.0VDC; works for me. If you would rather do it yourself than spend a few dollars for the USB supply then have at it.

Greg

[Lake-Effect]

Originally Posted by Boulter

Are these switching regulators? I also have a GPS that needs to be wed to the VHF. If they are just linear regulators, I should have a few dozen 7805s and the like kicking around.

Linear regulation (eg 7805) will work... just be aware that whatever power your GPS takes, the regulator will be dissipating around 7/5 times that value which gives you a conversion efficiency of around 5/12 or 42%.

The GPS won't take all that much power... so a 7805 would be acceptable, I expect. Measure the current so you know how much power the 7805 will dissipate, which might require a heatsink.

[CarinaPDX]

The USGlobalsat MR-350P is spec'ed to draw 80mA, at 4.5-6.5VDC. (The USB spec requires the provision of 500mA, at 5VDC.) Pretty much anything will do the necessary job - just not sure it is worth it.

Greg

Edit: The MR-350P uses a SiRF Star III GPS chip, which is in many of the GPS products and is one of the best, so should be representative.

[Boulter]

Originally Posted by CarinaPDX

Pretty much anything will do the necessary job - just not sure it is worth it.

Yes, my device draws 90mA according to specs, so can't get much easier than a 7805 which I have than a USB charger which I don't. Did a dry run on the bench with the bench supply. It seems to work. I say seems because the symbol on the display of the VHF flashes with the GPS connected, and doesn't when removed. That is the extent of the engineered in diagnostics.

Boulter

[wstu]

I know that this topic is 6 months old but thought I would interject what I have learned. regarding the 7805 I found someone say,
"Forget using a 7805 regulator unless you have one on hand, and have room for a fat heatsink. Go to a "dollar store", thrift store, or flea market, and buy an obsolete car charger for a cellular phone. These typically contain an a small circuit consisting of about a dozen components, primarily a MC34063 switchmode-regulator chip (an 8-pin integrated circuit) that is much more efficient than a 7805 (and therefore waste less energy as heat)."
How can I convert 12v down to 5v?

[wstu]

Again I know I am late but if CarinaPDX is still out there, will the USglobal BU-353 work in your system?

[CarinaPDX]

The model that I use (MR350P) is NMEA 0183 compatible, and I use one of the NMEA 0183 inputs to the Furuno MFD. The BU-353 has a USB interface, not NMEA 0183, and I believe would not interface to the single USB interface on the MFD (there are mouse/keyboard drivers for the USB but I doubt there is the necessary driver for the USB-RS422 chip inside the GPS). I have used the BU-353 model with my Mac to good effect so I can recommend it for USB applications.

Greg

[andreanuzzo]

Hi all,

I have a similar problem.

I am attempting to connect my autohelm course computer to my laptop via RS232.

On the course computer I have

nmea in+
nmea in-

nmea out+
nmea out-

Question: which of the RS232 wires do I connect to?

Thank you in advance for your help.
Andrea

[nohal]

While it *might* work and usually does with most of the RS232 chips nowadays in use, RS-422 and RS-232 are not electrically compatible by definition.
Read this document to learn something about it. Note that "NMEA +" translates to "NMEA A" and "NMEA -" to "NMEA B"

Pavel

[CarinaPDX]

If you are trying to provide cross-track error (XTE) from the laptop to the autopilot, then you want to use the NMEA IN +/- connections on the autopilot.

What are you using to adapt NMEA to your laptop? It is pretty rare to find a laptop with RS-232 these days...

Greg