DH485 Network Layout (Picture) - Questions about AqualinkRS Dual DH485 Terminals, Terminating Resistor(s), and Baud Rate / Cable Length

[halfspec]

Good afternoon

Thank you for all the hard work going into this project. I am very excited to get started.
I am basically coming from a setup that did not include an aqualink rs control station and building one in from scratch with the hope of using AqualinkD from the start. My OG setup involved a VSFLOPRO pump and a TRUCLEAR chlorinator that I manually controlled with a speedset control panel + the truclear's built in keypad. Extremely basic, so I'm looking forward to adding the RS and AqualinkD to hopfully get full automation through the web interface and home assistant via mqtt.

I'm in the planning and purchasing phase now and wanted to ask a couple of questions related to the DH485 network before I break ground. My plan is to daisy chain in this order: USB-RS485-WE-1800-BT -> Aqualink RS8 (Rev T.2) -> VSFLOPRO -> TRUCLEAR. That should look something like this:

My questions are:

1. Do you see anything fundamentally wrong with this layout?
2. I believe the USB-RS485-WE-1800-BT already has a 120ohm terminator built in (at least from the pictures I stole off the internet (I haven't got mine yet)). If that's the case, I would only need to put one more 120ohm resistor in parallel with the TRUCLEAR DH485 connection correct?
3. Is my use of the dual DH485 headers on the Aqualink RS8 kosher / equivalent for a daisy chain hop?
4. Are there any concerns with lengthening the DH485 wiring of the USB-RS485-WE-1800-BT adapter to ~ 75ft? The pi 3b I plan on using is already living in my network rack and I would like to keep it that way as it is climate controlled. I work with RS232/DH485 serial protocols at work and usually length isn't an issue until you start seeing propagation delays that are incompatible with a chosen/faster baud rate. In that instance, stepping down the speed of your baud rate usually fixes the issue. For < 100ft I doubt any of this matters, but I wanted to ask and I wanted to see if lower speed baud rates are a thing with the Aqualink DH485 network or if the baud rate is locked to a known rate?

I believe that's it for now. I very much appreciate any advice
Lane

[sfeakes]

Your wiring in theory looks good. And I’m sure will work. One problem is no pool manufacturers tell you what devices are and are not terminated even different revisions of the same device and have different termination. What may work better is to wire both the VSP and the SWG directly to 1 set of terminals on the panel, and the RS4852USB adapter to the other. There is usually no issue with dumping multiple devices to one set of terminals if the wire length is short.

1. No issues, it should work, but above might work better. BTW The serial logger with AqualinkD is great for uncovering RS485 issues and showing you which connections work best.
2. No, personally I’d leave the jandy devices as is. Most equipment is terminated by default. It’s the keypads and interfaces that you can never tell if they are terminated.
3. Yes. They are linked together anyway, they are no individual RS485 bus.
4. With quality cable no issues at all. And yes the USB-RS485-WE-1800-BT has termination. (You simply connect 2 wires together to enable the resistor)

[sfeakes]

I just notices you have 4 wires from the USB-RS485-WE-1800-BT connected in your diagram. DO NOT DO THAT, you will break it. Connect only A & B (or data + & data -), optional the ground. Do not connect the power wire to the USB adapter.

[halfspec]

Thank you very much @sfeakes. I'd like to think I would have caught the power wire mistake when I triple check myself, but assuming not, you saved me a huge headache. I am indebted to you. I have edited the OG pic and will work to replace the one posted above to try and limit confusion to anyone else who may stumble upon this thread.

I'll keep your suggestion in mind with regards to landing the VSP and SWG together on one dh485 block in the control panel. I could see how that would probably create a better network from a resistance standpoint 👍.

10 4 on leaving the jandy device termination alone.

Glad to hear the comms logs are so comprehensive. I can work with that!

Thank you again
Lane

[halfspec]

I have a quick follow-up on the first reply

Is it generally recommended to connect two Terminator 120R wires on the USB-RS485-WE-1800-BT up front? Or is it something you only connect if you're having problems? I'm having problems ;)

Lane

[sfeakes]

Only connect the terminator wires if you are having RS485 issues. By default leave them not connected.

[halfspec]

Thank you. I'll leave it dis-connected for the time being since I haven't run the serial logger yet... which you're helping me with in the other thread :)

Appreciate your help
Lane