Marine Projects

NMEA-0183 is a marine data transmission standard, covering both electrical transmission and serial data content. V2.0 and higher are based on differential RS-422 transmission. This is a single talker/multiple listener architecture.

On my vessel, I needed a repeater (or buffer) to take the master NMEA-0183 data stream and distribute to more listeners than usual. Having just one or two listeners per driver circuit also minimizes the effect of cable problems (problems only affect THAT driver circuit). I wanted a NMEA-0183 input with multiple NMEA-0183 outputs. Having an RS-232 converter would be a bonus, allowing a PC to listen to (or drive!) the circuits. (Some GPS devices claim NMEA-0183 outputs but really only mean data content compatability, not circuit compatability - so the RS-232 portion here may be helpful for that.)

Thus my NMEA-0183 Repeater/RS-232 Converter project was born. This is a 5cm x 5cm printed circuit board with the NMEA-0183 reference design input (optoisolated with overvoltage protection), 4 driver circuits, and a bidirectional RS-232 circuit. A vessel 12V power input connection drives the card.

Cost for parts alone (June 2011) is just about $11.60 in very small quantities. Note: hand soldering the Maxim uMax10 surface mount package is not for the unskilled. Here are the design files available for the NMEA-0183 Repeater/RS-232 Converter:

• Eagle Schematic File
• Eagle Board File
• Zip of all Gerber files needed to have PCB fabricated
• Excel Parts List
• PDF of Schematic

The next step was to remove the RS-232 connection from the repeater and replace with a USB serial connection, and power the entire card from the USB cable.

Cost for parts alone (June 2011) is just about $10.50 in very small quantities. The FT232RL USB serial chip is an SSOP 28 pin surface mount package. You will need a USB cable that connects to a USB mini-B connector (similar to what is found on existing cameras, portable GPS units, and other mobile devices). The USB connector is a surface mount connector. Here are the design files available for the NMEA-0183 USB Connection:

• Eagle Schematic File
• Eagle Board File
• Zip of all Gerber files needed to have PCB fabricated
• Excel Parts List
• PDF of Schematic

The Virtual Com Port drivers to support the NMEA-0183 USB Connection for many operating systems are available from the USB Serial Chip (FT232RL) manufacturer, Future Technology Devices International Ltd, at this link.

This was the original marine project. The goal was a cheap (<$20 in 2000 parts cost) microcontroller-based horn controller that would sound several NavRules-required sound patterns for a power vessel automatically. The user interface was a 6-position rotary switch (one position is off). The horn interface was a power-agnostic 16A contact closure. Three units were hand-constructed on perf board in the summer of 2000, two have been in service for 10 years in the marine environment. A complete user manual had been written for the original hand-constructed version. Now, an etch-based version (Rev B) is being prepared to replace the originals, which are showing some slight corrosion on exposed metals. With etch, a few component differences are possible and some minor engineering changes have been made based on the 10 year field experience.

The Rev B etch version uses the original PIC12C508A microprocessor type and operating code (although provision to be able to substitute the 12F629 has been made). Over 10 years of usage, no needed additions or problems have ever developed!

Parts-only cost looks to be less than $6. The printed circuit board cost looks to be around $8.70 (per unit cost plus amortized vendor shipping fee). Here are the design files available for the Restricted Visibility Horn Controller:

• Eagle Schematic File
• Eagle Board File
• Zip of all Gerber files needed to have PCB fabricated
• Excel Parts List
• User Manual
• Zip of all PIC source code/project files
• PDF of Schematic

This is the rebirth of a very old project, never completed but with many parts acquired a decade ago.

The NMEA-0183 Repeater above just buffers and distributes an existing data stream. If there are multiple data streams that need to be aggregated, a multiplexer is required that listens to all the required streams and re-assembles the content into a single output stream.

I have a variety of on-board NMEA-0183 data sources, some which have redundant data...GPS receiver, flux gate compass, water depth and temperature, chart plotter, radar, PC chart plotting software, and probably more. The original project was to be able to take 4 NMEA-0183 streams and provide a single output. Some effort is needed to avoid data replication...such as repeating position data that derives from a single instrument but which appears on several data streams already.

A fair amount of engineering was done long ago; some of the challenge now is locating both the electronic and paper copies of that engineering work to see where I really stand, and where the availability of add-on PCBs to the existing single board computer design would accelerate (read: no wire wrap) the effort. More to come on this project.