Connecting Garmin GHC/GHP20

[schnapsy]

Hello Luis,

I want to connect the Garmin GHC20 / GHP20 autopilot for transmission (for HDG) AND reception (for GPS or wind sentences).
This is possible according to the diagram below.

My question: for the transmission (from Garmin to Nmea4Wifi), I plug the TX/A and TX/B cables (numbers 3 and 4 on the diagram) on the A and B of an Nmea4wifi input.

But where do I connect the RX/A and RX/B cables (5 and 6) to receive GPS and / or wind phrases on the Garmin from the multiplexer ?

Do I have to connect them to the output (but in this case how fast?), knowing that on this output, a serial / usb cable is currently connected to go to the PC in 115200 bds.

[Luis Sa]

Hello,

As far as I understand your question you have an USB cable connecting the multiplexer to a PC. I do not know if your are sending data from the PC to the multiplexer, sending data from the multiplexer to the P3 or both.

The important thing to remember is that data going out on the P5 output is simultaneously going out on the USB port. If you also want to deliver that data to a Nmea183 listener, I think you should decrease the data rate. Nmea183 devices are not capable of receiving data at 115200 baud. So you will need to slow down the communication with the PC.

I recommend to use A5 connected to RX/A (pin 5) and GND connected to RX/B (pin 6). If you are sure that the pair (pins 5 & 6) form an opto isolated input you could use B5 instead of GND. In non optocoupler inputs the RX/B is normally GND and if you connect B5 to it you are actually short circuiting B5. I am considering to revise the multiplexer to remove B5.

Hope that this information is useful,

Greetings from Tints, Greece

[schnapsy]

Hello Luis,

Thank you for this quick response.
I should not have mentioned the USB cable because it is not important (I installed it only as backup if WiFi no longer works) and I can disconnect it.

So, if I refer to the last paragraph of your answer, if I connect A5 to RX/A (pin 5) and GND connected to RX/B (pin 6), at 4800 bds, I get the GPS information from the multiplexer on my Garmin.

That's exactly what I want and I thank you.

Have a nice stay in Greece (and a little thought to those who are held in their office !)