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Hoping to get some help on setting up a NodeMCU (esp8266) with this 1 arduino library to control a Variable Frequency Drive (VFD).

I'm afraid to say that I almost need help from square one, as I'm completely new to the modbus protocol, and both the library and the VFD are (to my newbie brain atleast) very lacking.

What I have done so far is get a Node MCU and a MAX485 module hooked up, and connected it to the RS485 terminals on the VFD.

However, the only documentation that the VFD provides is the following (see screenshot). I understand that I need to somehow structure this in a Modbus RTU call as a hex value, but I honestly do not know where to even begin.

All I want to be able to accomplish is to set the frequency, and then start and stop. Potentially read a few values such as current draw, but thats overkill for now.

I'm also not attached specifically to this library, its just what I found that was compatible with ESP8266. I also have ESP32s if thats a better / easier option.

Apologies for the severe lack of actual progress here, but really hoping someone more clever than myself can help here.

enter image description here

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  • \$\begingroup\$ Have you tried searching for ESP32 MODBUS + "example" or "tutorial". I'm sure it's easier to adapt a working example to the specific needs of your VFD than to start from scratch. \$\endgroup\$
    – Spehro Pefhany
    Jan 27 at 23:04
  • \$\begingroup\$ do you have a USB-485 adapter? Running the VFD from a PC or MAC should help get your mind around simple Modbus. \$\endgroup\$
    – david
    Jan 28 at 0:17
  • \$\begingroup\$ That table is very poorly worded. Modbus sees the world as 16bit ‘registers’ and single bit ‘contacts’ and ‘coils’. Here we’re only concerned with registers. The column ‘address/hex/word’ is simply the register address. So to stop you would write the value 2 to register 3. To go forward, write the value 1 to register 3. To get the bus voltage, read register 8. And so on. Modbus rtu is quite simple so rather than use a library, you could create the byte sequence of the modbus operations you want to do. Tools like Modscan for the PC will show you the required bytes to send. \$\endgroup\$
    – Kartman
    Jan 28 at 12:56
  • \$\begingroup\$ Thanks everyone for you help and suggestions. Spehro, I did end up finding a few examples, though not controlling a VFD specifially. David, no sadly I do not. Kartman, thank for the breakdown, thats super helpful. I’ll play around with that. Thank you! \$\endgroup\$
    – Christian Carlsson
    Jan 28 at 17:02

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