Waveshare Industrial Modbus RTU 8-Ch Relay Module with RS485 Bus, Multi Isolation Protection, 5V Voltage

You can get the relays to toggle, but if you expect to read anything back from this device you're going to have to ignore the 3.5 character minimum response time, because this device responds in 1 character time. Waveshare tech support is useless.

This is a really nice Mobus RTU 8 Channel Relay. Everything works as I expected.It responds to Modbus Read and Write Coil commands, and has a non-standard code to flip a coil.It uses register 4000 hex to set the Slave address.The case is very nice and I particularly like having both DIN Rail and through hole mounting options, it's much more professional than an open circuit board, and worth a few dollars more to have the protection and DIN rail mounting.It has a status LED that blinks when the unit is running, as well as Transmit and Receive LEDsIt comes with a power adapter, with the correct plug but also has 5V screw terminal inputs if you want to hard wire it to an existing system that already has a 5V power system.I've had this unit for several months hooked up to my development computer and used it for testing my software, and I often times wished it had LEDs for the relays... well.... for some reason I picked it up today while it was powered up.. and found out... IT DOES!!!! It has actually very nice blue LEDs on the circuit board just behind each relay contact connector, They are surface mount LED's and you can't tell they are there when the device is off.. and I never thought to look for them because I didn't see any holes in the case for an LED.. but there IS actually a small gap between the case and the relay contact connectors.. and if you don't happen to have the device at an angle where you can't see straight into it, you would never see the LEDs... Well I was pleasantly surprised by the status LEDs and now that I know they are there, I can't help but see them. This was the one thing I wished this had and it had it all along, just hiding. I'm so happy it has the coil status LEDs that I thought this device now deserves a 5 star review. Great Product, at a reasonable price, and it works really well... and it has Status LEDs!

I love listening to the relays click on and off. It looks very professional. The product does what it says, but...They really need to make it clear where to get the manual. I had to hunt through their website and found it on the wiki - "Modbus RTU Relay", which lead me to the "Protocol Manual of Modbus RTU Relay". I completely overlooked the wiki link at the bottom of their product page.The protocol is a bit wonky where function codes are being applied to addresses that would normally be out of range. I stumbled along for a bit, trying to read coils. You can't - at least, not in the way you would expect. You can write to coil 0 (channel 1), but not read from it. For that, you'll need to read 8 bits from coil 256... yea. Most software will only show you the first bit. Coil 257 doesn't exist, so you can't ask for two bits either. Since you can't read anything from the first address, the scanning software that I was using wasn't detecting it either.