The central part of the Nmea2Wifi multiplexer is the ESP8266 module named as Wemos D1 mini and referred to as U2 in the circuit diagram. If an Access Point is created by the multiplexer and you get the "Settings Web Page" when you type 192.168.4.1 in a browser, then the ESP8266 module is OK. The little antenna printed in its PCB has a sufficient range for most applications in the confined space of a recreational vessel.
If the ESP8266 module does not create an Access Point, check if it is inserted in the right position in its socket. If it happened that you removed it by some reason and inserted it back the other way round, you can recover from this error as the module is not destroyed.
The same is not the case if you invert the power supply, that is, if you exchange the 12V and the GND terminals. Most probably you will destroy (with smoke) the voltage regulator referred to as U1. This circuit is a step down switching voltage regulator that creates 5V to feed all the components in the multiplexer. After September, 1, 2017, versions of the PCB are supplied with a protecting diode so that a wrong connection will not destroy the voltage regulator. If you have an older unit and want to add that protection see this article.
In addition to the ESP8266 module and the voltage regulator there exist two Nmea 183 serial inputs and one Nmea 183 serial output. In normal operation you have the following meanings for the LED lights:
- BLUE LED in the Wemos D1 mini - blinks when data is output on the P#3 serial port. I also blinks for a second or two when the multiplexer is powered ON.
- GREEN LED in the main PCB - blinks when valid data is read by the ESP8266 on the P#1 serial input.
- RED LED in the main PCB - blinks when valid data is read by the ESP8266 on the P#2 serial input.
Note that the blink of the BLUE LED is a not a warranty that data is output at port P#3. This so, because between the ESP8266 and the output itself, there exists a driver integrated circuit, MAX485, referred to as U5. If this U5 fails, data does not reach the output port. On the contrary, if the GREEN or/and the RED LEDS blink it means that the corresponding data has passed through the optocouplers 6N139 referred to as U3 and U4. If one of these LEDS do not blink there is a chance that
- The external units that feed the multiplexer are not working
- There is a mismatch of baud rates
- The connections between the external units and the multiplexer are not correct
- Or, there is an hardware fail on the optocouplers of the multiplexer
I will try to explain how it works. Whenever the multiplexer receives power, the first thing it does is to determine the mode of operation (AP or SAT). It does that by reading a location in EPROM memory. If this location shows that the module is in a factory state (either because you did not change any of the initial settings or because you had pressed the RESET button), then it does this (after firmware 4.1):
- it writes a sequence of 10 HIGH and LOW voltages on P#3: HIGH LOW HIGH LOW HIGH LOW HIGH LOW HIGH LOW
- and reads P#1 and P#2 to look for that same sequence. At the first fail it gives up and proceeds as normal, that is, initiates the wifi functions, adjust the parameters and so one.
- writing 5 times in 5 seconds the string "TESTING P#1 AT 9600 BAUD RATE" on port P#3 (BLUE goes ON) and reading that string on P#1 (GREEN goes ON if something arrives)
- lighting RED LED during 0,1 seconds if all the 5 strings arrived without errors
- pausing 1 second
- writing 5 times in 5 seconds the string "TESTING P#2 AT 38400 BAUD RATE" on port P#3 (BLUE goes ON) and reading that string on P#2 (RED goes ON if something arrives)
- lighting GREEN LED during 0,1 seconds if all the 5 strings arrived without errors
Note that power to the multiplexer is supplied through the USB cable connected to the ESP8266 module. If you do the same experiment and your LEDs blink as in the video then you are sure that all the hardware in the multiplexer is working as expected. So, reconnect the multiplexer as normally and if something is wrong, look elsewhere!