# Pi zero w, modbus rtu, arduino

**URL:** <https://discourse.nodered.org/t/pi-zero-w-modbus-rtu-arduino/32699>\
**Category:** Industrial\
**Created:** [10 September 2020 14:48 UTC](https://discourse.nodered.org/t/pi-zero-w-modbus-rtu-arduino/32699 "2020-09-10T14:48:38Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![juan1](https://avatars.discourse-cdn.com/v4/letter/j/bc79bd/32.png) [@juan1](https://discourse.nodered.org/u/juan1)\
**Post date:** [10 September 2020 14:48 UTC](https://discourse.nodered.org/t/pi-zero-w-modbus-rtu-arduino/32699/1 "2020-09-10T14:48:38Z")

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Hello everyone.  
I'm trying to connect a pi zero w with an arduino UNO using modbus rtu protocol. I use the usb integrated on pi pcb to connect to arduino's usb.  
Arduino has a modbus program that I tested before with modscan and works properly, but I can't connect node red with it. I'm working with modbus read node from modbus contrib.  
I can't find out what is happening. I tested all kind of baud rate, format message and different servers(ttyacm0, ttyso, ttyserial1, ttyserial2 but It doesn't work.  
I notice that node-red can't send any message to arduino because comunication lights on arduino pcb are always off.  
Could anyone please help me with this?  
Thanks

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**Author:** ![mtoko](https://sea2.discourse-cdn.com/flex026/user_avatar/discourse.nodered.org/mtoko/32/138_2.png) [@mtoko](https://discourse.nodered.org/u/mtoko)\
**Post date:** [11 September 2020 13:17 UTC](https://discourse.nodered.org/t/pi-zero-w-modbus-rtu-arduino/32699/2 "2020-09-11T13:17:10Z")

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Hi

Have a look at this article about configuration of the serial port on a Pi

> **[Configuring The GPIO Serial Port On Raspbian Jessie and Stretch Including Pi...](https://spellfoundry.com/2016/05/29/configuring-gpio-serial-port-raspbian-jessie-including-pi-3-4/)**
>
> The Raspberry Pi GPIO serial port configuration has changed under Jessie / Stretch / Buster and also with the Raspberry PI 3 / 4. How to set it up.

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**Author:** ![juan1](https://avatars.discourse-cdn.com/v4/letter/j/bc79bd/32.png) [@juan1](https://discourse.nodered.org/u/juan1)\
**Post date:** [11 September 2020 16:22 UTC](https://discourse.nodered.org/t/pi-zero-w-modbus-rtu-arduino/32699/3 "2020-09-11T16:22:35Z")

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Thanks a lot. You are very kind.  
Finally I did it. I did install raspbian and node-red again and everything started to work.  
I'm going to struggle with how to represent data on debug window. As you notice, I'm a beginner on node-red and on many other things related about code.  
Have a good day.

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**Author:** ![system](https://us1.discourse-cdn.com/flex026/uploads/nodered/original/1X/d073cd938eafa2e558d7c2cd59003b3ef4963033.png) [@system](https://discourse.nodered.org/u/system)\
**Post date:** [10 November 2020 16:22 UTC](https://discourse.nodered.org/t/pi-zero-w-modbus-rtu-arduino/32699/4 "2020-11-10T16:22:50Z")

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