The M7-GX series of GPS transponders may be directly connected to any Raymarine A, C, E or G series display. All of these Raymarine displays have at least one NMEA-0183 port. This allows them to be used with Raveon’s RavTrack series of GPS radio transponders to make a complete GPS tracking system. For this article, the Raymarine E80 product will be used as an example but the other models in the Raymarine line have similar integration steps.
When connected to the M7-GX GPS radio transponder, the E80 map will show the location of the user plus the location of all other transponders within radio range. This unique feature allows a user to quickly, easily and inexpensively make a portable AVL system for tracking cars, trucks, racecars, construction equipment or anything Raveon’s M7-GX transponder may be installed on.
The Raymarine displays have a built-in interface for NMEA 0183 devices, a serial data port intended for RS422/RS232 operation. The Raymarine E80 supports RS232 levels on the communications lines as well as the RS422 levels. Since RS422 was designed for differential signaling, there are pairs of signal wires instead of a single-ended ground that is shared between the Rx and Tx lines. For an RS232 protocol, one can tie the two negative wires of the NMEA 0183 signal pairs together to act as the ground.
The NMEA 0183 defaults to 4800 baud, 8 data bits, no parity, 1 stop bit, no handshake (4800-8-N-1). It is used to exchange way-point and other information between displays, GPS devices, and transponders.
When Raveon’s M7-GX transponder is connected to the Raymarine E80 using the NMEA 0183 connection, the GPS radio transponder can put icons on the screen of the E80. As the transponder receives updated positions from other vehicles, it updates the position of the tracked vehicle icons on the E80 display.
Raymarine E80 Wiring
The Raymarine E80 has the 5-pin NMEA 0183 connector shown to the right, located on the rear of the unit. NMEA 0183 is a common communications format for marine applications. See the following diagram for general wiring connections.
The recommended cable for interfacing to this NMEA 0183 port is the R08004 NMEA cable. It is a 5-wire cable with an Rx pair (differential + and -), Tx pair (differential + and -) and drain wire (unused). For the case of the E80-M7 system, the only used connections will be the white wire (NMEA input +) and the green wire (NMEA input common). These NMEA 0183 cables come in various forms so make sure to verify that the correct wire pairs (Rx, Tx or both) are included in the cable assembly before purchasing. Here is a picture of the full cable assembly with both Rx and Tx wires:
Wiring the Serial Cable
The E80 NMEA 0183 port must be connected to the M7-GX GPS transponder. This connection will allow the M7-GX to put icons on the screen of the E80 display, showing the location of other tracked vehicles. The M7-GX GPS transponder uses a 9-pin DB9 as it’s serial connection. Solder the E80 data cable wires onto a DB9 connector and plug the DB9 into the M7 transponder as shown below:
Connect the white wire (NMEA input +, pin 2) on the R08004 cable to the serial data output (pin 2) on M7-GX DB9 connector. Then, connect the green wire (NMEA input -, pin 1) on the R08004 cable to the ground of the M7-GX DB9 connector. You do not need to connect the brown, yellow or braid wires on the R08004 cable so you can trim them off if desired.
Configuring the E80
Verify that the serial data communications are set to 4800 baud-8-N-1 on the E80.
Configuring the M7 GX Transponder
Raveon has a designed the M7 GX transponder to work with the E80 display or any other NMEA 0183 display that can accept the “$GPWPL” NMEA message. The $GPWPL is an industry standard message that many GPS displays interpret as a waypoint command. The M7 GX outputs this $GPWPL message to put icons on the screen of the E80, and to move the icons around on its screen.
To configure the M7 transponder to output the $GPWPL message, set the M7 GX to GPS mode 4. To do this, put it into the configuration mode by send the +++ into the serial port. The M7 will respond with an OK. Type GPS 4 and press enter to put it into GPS 4 mode. GPS 4 is the mode that causes the M7 GX to output $GPWPL messages whenever it receives a status/position message over the air