How to test your Nmea3Wifi multiplexer

Discussion and support for the Nmea3Wifi multiplexer - a 2-input Nmea 0183 wifi multiplexer with a full bidirectional SeaTalk1 input/output port.
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Luis Sa
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How to test your Nmea3Wifi multiplexer

Post by Luis Sa » Wed Mar 29, 2023 10:16 pm


I really suggest that you test your multiplexer before installing it on your boat. You will learn about it and you will make a more confident installation. The 1st thing you can do when you receive a multiplexer (this is general for all the models) is to use a USB cable and power the multiplexer from a PC using that cable. Then you can check if the NMEA3WIFI network was created. You can connect to that network using the password 12345678 and typing on the navigation bar of a web browser. Then you can use Simulate Mode. You will see the green light on P1 to blink rapidly and, from time to time, you will also see the the green light on P2 to blink. If you did not change the default settings the blue led will also blink. Here is the meaning of the leds
  • green P1 led blinks when a fictitious sentence for GPS, wind and depth are sent
  • green P2 led blinks when a fictitious AIS sentence is sent (as only 2 moored boats are sent, the sending is sparse)
  • blue led blinks when there is WiFi data going out and coming in
If you go to the settings and check, for example, the box labelled as P2>P3 (meaning P1 should go to P3) and enter Simulate Mode again you will see that the red led for P3 (output port) also blinks when P2 led blinks.

If you have Navionics or OpenCPN or any other application capable of receiving WiFi nmea0183 data, this is the time to test. You need" to go" to the island of Lesbos in Greece to see "your" boat and 2 AIS targets.

You could also test reception/transmission by USB, UDP and TCP using Debug Mode and the the Nmea0183Tester tool but that is not the purpose of this post. Actually I would like to post here 2 videos that completely test the hardware of the multiplexer. I ask users to make this test before they suggest to return the multiplexer to me (which is very rare I must say :lol: ). Simulation Mode described above confirms that the ESP32 module is running OK, WiFi is working OK and that the leds also work OK but neither the transmitter on output port P3 nor the dual optocoupler integrated circuit that serves input ports P1 and P2, are tested. To do that you must do a loop. You need to connect the output of P3 to P1 and P1. This is shown in the videos below. Each time you do an Hard Reset by pressing and holding the BOOT switch and releasing it just after the leds go off, the multiplexer sends some specific code on P3 and reads it on P1 and P2. If it sees on P1 or P2 the data it sent on P3, the multiplexer enters an infinite loop:
  • 1 - sends a chunk of 500 zeros and ones on P3 at 9600 baud and blinks red light
  • 2 - reads P1 and checks if the exact 500 zeros and ones are received in the same order
  • 3 - repeats 1 and 2 at 38400 baud
  • 4 - if no single error is detected it blinks P1 green led
  • 5 - does 1 2 3 and 4 but this time it reads P2
  • 6 - sends the chunk of 500 zeros and ones to the SeaTalk1 bus (DATA line) and blinks red ST1 led
  • 7 - reads the DATA line and checks if it can read what it is sending. If yes, it blinks the green ST1 led
  • 8 - goes to 1
You need to switch off the power and remove the foldback wires for the multiplexer to skip this Self Test. With a USB cable you can make the test for ports P3 P1 and P2 as in this video:

If you also want to test the ST1 bus you need to power the multiplexer from the 12V and GND screw connectors:

You can use even a small 9V battery for this test. I have a small Gel battery when I do my tests:


I hope this is useful, Regards, Luis

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