This multiplexer allows bidirectional serial and wifi communication between yoursmart-phone, tablet or laptop and your boat instrumentation. The system has four opto-isolated Nmea 0183 input ports and one Nmea 0183 output port. The system also has an input/output USB port. One of the 4 input ports can be configured to receive SeaTalk1 data which will be converted to Nmea 0183 data. Wifi communication can use both the UDP and the TCP internet protocols. In total there can exist 6 input streams of data (4 serial, 1 UDP and 1 TCP) and 3 output streams of data (1 serial, 1 UDP and 1 TCP). The 6 input streams can be filtered, combined and transmitted to the receivers on any of the 3 output streams. Serial output can also be filtered. You can use this multiplexer in different ways. You can use it with a PC running navigation software such as OpenCPN or you can use it with several free Apps for Android or Ios. In addition you can get Sonar Chart Live maps on your Navionics Boating HD app.


Microcontroller: ESP32 (2 cores – 4MB – 240 MHz)
Power Supply Voltage: 7V up to 16V DC
Power Consumption:
   less than 90mA with Wifi On
   less than 45mA with Wifi OFF
   less than 10mA with Wifi OFF and Serial OFF
Nmea 183 Input Ports: P1, P2, P3, P4 - optical isolated
Nmea 183 Output Port: P5 - RS-422 compatible
USB Port: based on P1 and P5
SeaTalk1 Input Port: based on P4
Baud Rates:
   P1 & P2 (4800, 9600, 19200 or 38400
   P3 & P4 (4800 or 9600) 3840
   P5 (4800, 9600, 19200, 38400, 57600, 115200)
Nmea 0183 Sentence Filtering: on the 6 inputs and on the serial output
Firmware Update: Over The Air (without cables)


The power supply and the serial ports use screw connectors with printed labels in the PCB. The labels for the power supply are 12V (positive) and GND (negative). The 4 serial input ports have labels AN and BN where N (1, 2, 3 or 4) refers to the port number. If your Nmea data is available though a differential port, you connect its A (or Nmea+) terminal to the multiplexer AN and its B (or Nmea-) terminal to the multiplexer BN. If your Nmea data is available through a single ended port (such as RS-232) you connect its Output terminal to the multiplexer AN and its Ground (or common) terminal to the multiplexer BN. The output serial port uses a 3-way screw connector with labels A5 B5 and GND. If the receiving device has an opto-isolated port, you connect A5 to the A (or Nmea+) terminal of the receiving device and B5 to the B (or Nmea-) terminal of the receiving device. If the input port of the receiving device is not opto-isolated you should take special attention to the connections. You should connect A5 to the input terminal of the receiving device and not use B3. In addition, both GNDs (multiplexer and receiving device) should be connected together. In order to connect the SeatTalk1 bus to the multiplexer you connect the +12V line (red wire) to A4 and the data line (yellow wire) to B4 on the P4 connector.


The module is totally wifi configurable. When you supply power to the multiplexer for the first time, it starts with factory settings and it will automatically create a wifi network named NMEA4WIFI. You should disconnect your smartphone (or your PC) from other networks (if possible turning mobile data OFF) and connect to this NMEA4WIFI network using the password 12345678. When you are connected you write in the navigation bar of your browser and you will receive a web page which allows you to fully configure your module.


If you forget a password or if you have trouble with the operation of the multiplexer, you can, at any time, return to default factory settings by pressing and holding down for 2 seconds the switch labelled “Boot” on the Wemos module. For more support, please visit: or use the email <luis at vela-navega dot com>. In this website there is a forum dedicated to the Nmea4Wifi multiplexer with questions and answers from other users.


This web page is the response you receive when you type in the navigation bar of your browser after you connect to the NMEA4WIFI network. Note that the page will not respond to the commands SET, HARD RESET and UPDATE as it is not running in the multiplexer. Please see the sections in this site that describe these functions.


The Nmea4Wifi multiplexer is available in 2 versions: TH (Through Hole) and SMD (Surface Mounting Devices). They have the same functionality and only differ in the manufacturing technology. There are small differences shown in the following pictures. One difference is the position of the USB micro socket. In both cases the cover box can not be mounted when you use a USB cable. 

Multiplexer Box TH Version SMD Version