TUTORIAL: How to make MODBUS work with ESP32 - Arduino - RS485 - Part 2

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I was trying to get modbus to work with ESP32 for a long time. Eventually after finding no material online, I decided to look into it myself. Here is the problem and the solution.
For those who wish to support the channel, my Patreon account is here: / antonycartwright

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Опубликовано:

13 июл 2018

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Комментарии : 47

@danilocarrara7494 2 года назад

Hi ! good to see your video! I was seeing for a material to understand ESP-32 and MODBUS and it's nice to find it to not reinvent the well and lost a lot of time.Thanks

@turb0t 2 года назад

I found this very useful. I was trying to get the ESP8266 to work with a MAX485 in Esphome, and the remote device was never responding. I purchased one of the logic analyzers you used for checking the serial protocol, and I found that as well as the modbus serial data being sent to the MAX485, the debug log was also sent to the serial port - this was even though I wasn't using serial to view the log, and I was applying OTA updates. I have spent weeks trying different things and testing , and the logic analyser identified this in a few minutes. Well worth the £10. the MAX485 is now working across the other uart on GPIO13 and GPIO15

@justapasttime1502 Месяц назад

I'm seeing a similar problem. Thanks for commenting on this.

@tlangdon12 2 года назад

Thanks Antony. I learned alot from this video and part 2.

@catalinpetcu6202 5 лет назад

Anthony, how do I read the values received? Thank you

@andradecaio_ 2 года назад

Hi Anthony! Tks for sharing your solution. Do you got any issues with parity bits and start/stop bits over the ModBus communication line?

@andreapiccini23 5 лет назад

I've gone crazy with that for a month at work, my buffer is a ADM2582E and it happens the same thing because i designed with a 10k resistor pull up in A and pull down in B 10k is too much high and sometimes modbus signal for long distances go down below 5V, so pull down and pull up R is seen by buffer as an open circuit, then buffer force the pin randomly up or down, so the solution is a 5K resistor for me instead of 10K,put like you did. Seems a common problem for modbus communication buffers

@lewisbarnard3606 6 лет назад

Thank you for the solution!

@muralisubramaniam5622 3 года назад

Hi Antony, I have been struggling for quite sometime with the modbus.. This solution could work for me, but I am not sure how you have arrived at the CRC. I am getting so many solutions or CRC, have tried multiple algorithms but unable to get what you are getting which is 126 for MSB and 244 for LSB. which polynomial has been used? I have tried A001 and 8005

@AndreasDelleske 10 месяцев назад

Great video! However everyone should keep in mind that the 120 microseconds might work with a baudrate of 115200 (or whatever that was) but we'd need much more with 9600 baud. It would be awesome if we could just wait until the buffer is flushed...

@fingerprint8479 4 года назад

Hi, what is the command to read contents of a RS485 register? Thanks

@mukeshl7037 2 года назад

Hi can this be done with schnider energy meter to read holding register with esp mcu

@atifhussain3455 3 года назад

Any idea how to make ESP32 or Arduino as a Slave and recieve data from Modbus RTU over RS485?

@volador2828 4 года назад

Nice work!

@dj1encore 2 года назад

This is very useful, thank you for sharing it. Have you considered doing the same video using the rp2040. I assume that the rp2040 would be faster than the esp32. Is there an alternative to using blocking code for the delay.

@AntonyCartwright 2 года назад

Hi, I can't remember how the ESP32 works, but more often than not, there are ways around blocking. I did a project a few days ago where I could peek into the buffer to see how many bytes were in it before trying to read. This would completely stop the block as you wouldn't read if you know that nothing is there.

@europer67 11 месяцев назад

Question since your saying 2 times differently. The 680Ohm from vcc (5v) to A? BR

@qzorn4440 2 года назад

Modicon plc had developed in 1979 modbus and it is still used a lot. now to read modbus RS485 registers and go thru an esp32 bluetooth to a smart cell-phone like remotexy? thanks 🥳 yes, this is very useful when using so many esp32 spinoff pcb modules with home IOT and industrial PLCs 😊

@farazsayed5730 5 лет назад

Why don't you carry on using the library for everything else and just hook your de and re to another pin which you digitally write?

@grumetenavegando 5 лет назад

Thanks for the explication.

@oliverqueen7690 Год назад

hi can you make something how to get data on a mod address.. like how NPK sensor work.

@electronic7979 6 лет назад

Excellent project

@AntonyCartwright 6 лет назад

Thanks! :-)

@JL-tv4eu 5 лет назад

Reason for the problem is straight forward and has nothing to do with a particular microcontroller, in this case ESP32. Transmission of data bytes to the RS485 Modbus is done by separate UART hardware on the microcontroller. When you write a byte to a serial port, you transfer this byte from microcontroller to the UART transceiver inside the ESP32. UART transceiver will then transmit this byte out to the RS485 modbus transceiver during the certain time period dependent on the baudrate. So, if you look at the last byte that you transfer to UART transceiver and then immediately follow with changing the mdDeRE pin LOW. UART transceiver will take longer to actually transmit that complete byte to RS485 transceiver than what it takes to set mdDeRe pin low. Or if you can imagine it in another simplistic way as a bit time. To change mdDeRe pin takes 1 bit-time. To Transmit one data byte takes 8 bit-times (as 1 byte=8 bits). Obviously there is some other detailed timing involved in the whole internal data processing. But hopefully you can see why mdDeRe pin goes low before the last byte if fully transmitted.

@AntonyCartwright 5 лет назад

Yes, that's what this video is about. :-)

@chanchainilsalai1044 3 года назад

can i use board rate 500000 bps ?

@germanGGGG72 3 года назад

Thanks so much !!

@catthayippy491 Год назад

Do you have Part 3 of "How to make MODBUS work with ESP32 - Arduino - RS485 "

@cebubikebootcamp 9 месяцев назад

The way you put the terminating resistor it is not Ground to A it is VCC to A

@stuartajc8141 6 лет назад

Interesting, thanks. Audio is a bit choppy though

@AntonyCartwright 6 лет назад

Thanks, I'll have to look into it. It seems to be the screen recoridng software. :-(

@shamshersinghsaini1322 3 года назад

Hi can you provide this code

@Electronieks 5 лет назад

Thx

@shamshersinghsaini1322 3 года назад

will this code work with Nodmcu 8266

@alanmoreno6330 2 года назад

Either it does or it doesnt

@redikaak9986 2 месяца назад

it should be better if you provide wiring diagram instead of pointing the wire

@krishnakulkarni6574 6 лет назад

hi, I am trying to send data from pro mini to esp 32 but esp32 is not getting any data,showing response timed out. if i put uno instead of esp32 its working fine.

@AntonyCartwright 6 лет назад

Why would you send data from APM to ESP32 via Modbus?

@krishnakulkarni6574 6 лет назад

I havent found any one doing such communication so i wanted to try it with two different micro controllers communicating via modbus.Thanks for your response,still iam trying on it if you can suggest any help regarding this ,thanks in advance.

@AntonyCartwright 6 лет назад

Hi, it is possible, but it's hard work. It does work though just like in my video...

@krishnakulkarni6574 6 лет назад

I have used your method of working and also traditional method like modbus master library and modbus library for slave its not working

@AntonyCartwright 6 лет назад

The Arduino Pro Mini will work with Modbus Master but the ESP32 won't work with any known library. The only solution which I know is my one. If it is not working, you need to know why it's not working. Do you have a logic analyser? You're going to need one!