Low Cost Modbus Boards

I've been seeing a lot of low cost Modbus boards on Banggood and ebay, like an 8 input / 8 relay output board for around $10. One or several of these, coupled with an ESP32 could be a powerful piece of gear.

Has anybody here used any of boards? Documentation appears to be lacking, so it may take some effort to determine registers and so on.

Interesting devices!

Just been looking at some of the ones on ebay and found that a UK company is one of the resellers. They have a bit more info on their site, & note that the default modbus address is 255 but can be changed.
**broken link removed**

The modbus protocol is pretty well documented on Wikipedia, it looks straightforward enough.

>google< - And there is a PIC modbus library source for both master & slave units on github.

Definitely worth some investigation, thanks for publishing the info.

Thanks for the UK link. It does present things more clearly.

I was looking through some of the boards available at Banggood last night. There are a lot of different functions available and the gears are turning in my head.

Looks like Cat5 cable can be used for an RS485 network over short/moderate distances.

Visitor said:

Cat5 cable can be used for an RS485 network over short/moderate distances

Click to expand...

Yes, it should work fine & be OK for hundreds of metres, at moderate speeds with proper termination.
Just remember you also need a shared ground (or an earth at both local and remote devices) to keep the data line signals in common mode range.

I often use audio twisted pair like mic cable / starquad for short links or a proper data-rated screened twisted pair for longer links.
Van Damme 278 401 000 is nice stuff for fixed data wiring, I use a lot of that.