Question regarding USB to RS485 Cable

[mdallaire]

I am coming from this thread and am very excited at the idea of getting direct local control over my geothermal heat pump.

I am looking at the USB to RS485 cables on Amazon and saw those two variant on the one you recommend:

DSD TECH SH-U10L and DSD TECH SH-U11L

Can anyone provide insight as to what the difference is between the two and if I should stick to the SH-U10L or if SH-U11L would provide any advantage?

[ccutrer]

They use different UART chipsets. The SH-U10 has a CP2101N and the SH-U11 has a FTDI FT232. I personally have SH-U11 devices. I've had other serial devices based on other chipsets as well. My only bad experience I can remember is trying to get drivers for a CH340-based chipset on the Mac wasn't seamless, but I did end up getting it working.

[mdallaire]

Thank you for the answer, I just got my SH-U11L!
I am unclear on which wire goes in to which screw terminal on the USB. Your instructions mentions connecting 1 and 3 to A+ and 2,4 to B-.

How does A+ and B- translate when working with the following terminals :
TXD+
TXD-
RXD+
RXD-
GND

If you want I can submit a PR for the "Connecting to the ABC" section with what I learned so it can help others (like me) that are less knowledgeable about RS485.

[ccutrer]

On the RJ45, pins are from left-to-right, while looking down at the connector facing away from you. On "B" cord, that's:

1. White/orange
2. Orange
3. White/green
4. Blue
5. White/blue
6. Green
7. White/brown
8. Brown

Check the other end if your cable that your plugging in to see if they match that.

On the adapter, TXD+ is A+, and TXD- is B- (the RXD pins are used for RS-422 - full duplex communication).

[mdallaire]

Thanks for the clarification. I will submit a PR with more details for the readme.