How to wire a Sparkfun RS-485 breakout?

I am having a hard time understanding how to hook up a Sparkfun RS-485 breakout to my Arduino and soil moisture sensors. I bought the board here and the schematic is here. The schematic seems cryptic to me, particularly because the connectors are not all labeled on the board. I am using a Seeeduino LoRaWAN board which is like an Arduino Zero.

My sensor has 4 wires for input: ground, 4-24V DC, A, and B and uses and ASCII protocol

Here are questions and what I think may be correct - please correct me if I am wrong.

The 5 pins (holes, really) in a line on the left side are JP9 (the pins are labeled on the back) and are for connecting to the Arduino. Pin 1 goes to VCC - should I use the 3.3 V pin or the VIN? Pin 2, RX goes to TX on the Arduino (pin 1) and TX to RX on the Arduino (Pin 0). The RTS pin would go to a GPIO pin on the Arduino for manual control of the flow direction. Based on a different breakout, I would set this HIGH for transmit and LOW for receive. GND goes to the Arduino ground.

Moving to the part of the schematic around the chip, it appears that RTS is connected to both RE and DE internally, so I don’t have to make that connection, correct? On the other side does that mean VCC is connected to both VCC on the JP9 connector and the capacitor?

My sensor would get hooked to either JP2 or JP3, which have different pin spacing, but it looks like JP2 has a terminating resistor that I should only use at one end of the RS-485 bus. There is electrical continuity between the pins on JP2 and JP3 so I don’t see how the resistor can only be on JP2. I would like to solder in a screw terminal for hooking up the wires and I think that fits the one with wider spacing.

I guess that I don’t need to worry about JP4 and JP11, although I don’t have a clue what 1,2,3,5 are for.

Bonus question, why are some of the connections on the board square? Thanks!

RS485-Breakout-v13.pdf (17.6 KB)

According to the Sparkfun website, all those holes in the right hand side are to give the user the option of several different connector types.

This breakout board includes the SP3485 RS-485 transceiver, filter capacitor, and other components shown on the schematic. We've broken out the RS-485 output to three different connections: (1) an RJ-45 connector, (2) a 3-pin 3.55mm screw terminal, and (3) a 3-pin 0.1" pitch header; none of these output connectors come populated.

If you don't need the terminating resistor, then you will need to desolder it.

You should connect Vcc to 3.3v

When interpreting the schematic, any connections that are given the same label are connected. So all the connections on the schematic labelled "A" are connected together. Same with all the connections labelled "B", etc.

Looking at the schematic, the connector at the bottom of the board seems to be a breakout for other pins on the RJ-45 connector when it's fitted.

I forgot to say that sometimes pin 1 of a connector is indicated on a PCB by a square pad.

Thanks. That's a huge help.