# Serial node strangeness

**URL:** <https://discourse.nodered.org/t/serial-node-strangeness/50232>\
**Category:** General\
**Created:** [26 August 2021 20:42 UTC](https://discourse.nodered.org/t/serial-node-strangeness/50232 "2021-08-26T20:42:07Z")\
**Posts on this page:** 8\
**Page:** 1

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**Author:** ![SteveDonie](https://sea2.discourse-cdn.com/flex026/user_avatar/discourse.nodered.org/stevedonie/32/5212_2.png) [@SteveDonie](https://discourse.nodered.org/u/SteveDonie)\
**Post date:** [26 August 2021 20:42 UTC](https://discourse.nodered.org/t/serial-node-strangeness/50232/1 "2021-08-26T20:42:08Z")

</div>

I have a flow running on a Raspberry Pi that has two serial nodes that communicate with an Arduino - one for reading from the Arduino, one for writing back to it. Most of the time both nodes work properly, but for some reason right now the write node will connect successfully to the serial port but the read node will not. I've rebooted the Pi to see if that would help, but it did not.

Details:  
Raspberry Pi model 4  
Node red version 1.3.5

node-red-log reports the serial connection error:

```auto
Welcome to Node-RED
===================
26 Aug 13:48:15 - [info] Node-RED version: v1.3.5
26 Aug 13:48:15 - [info] Node.js version: v14.17.1
26 Aug 13:48:15 - [info] Linux 5.10.17-v7l+ arm LE
26 Aug 13:48:16 - [info] Loading palette nodes
26 Aug 13:48:18 - [info] Dashboard version 2.30.0 started at /ui
26 Aug 13:48:18 - [info] Settings file : /home/pi/.node-red/settings.js
26 Aug 13:48:18 - [info] HTTP Static : /home/pi/github/donie.us
26 Aug 13:48:18 - [info] Context store : 'default' [module=memory]
26 Aug 13:48:18 - [info] User directory : /home/pi/.node-red
26 Aug 13:48:18 - [warn] Projects disabled : editorTheme.projects.enabled=false
26 Aug 13:48:18 - [info] Flows file : /home/pi/.node-red/flows_poolcontrol.json
26 Aug 13:48:18 - [info] Server now running at http://127.0.0.1:1880/admin/
26 Aug 13:48:18 - [info] Starting flows
26 Aug 13:48:19 - [info] Started flows
26 Aug 13:48:19 - [error] [serialconfig:8290e893.ce4a18] serial port /dev/ttyUSB0 error: Error: Error: No such file or directory, cannot open /dev/ttyUSB0

```

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<div class="post-metadata">

**Author:** ![Gunner](https://sea2.discourse-cdn.com/flex026/user_avatar/discourse.nodered.org/gunner/32/43582_2.png) [@Gunner](https://discourse.nodered.org/u/Gunner)\
**Post date:** [26 August 2021 21:33 UTC](https://discourse.nodered.org/t/serial-node-strangeness/50232/2 "2021-08-26T21:33:39Z")

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On the RPi COM port designations tend to "jump" around.. one time being `ttyUSB0` and the next `ttyUSB1`, etc. There are many Googled references to this, and possible ways to lock the designations to a device.

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**Author:** ![SteveDonie](https://sea2.discourse-cdn.com/flex026/user_avatar/discourse.nodered.org/stevedonie/32/5212_2.png) [@SteveDonie](https://discourse.nodered.org/u/SteveDonie)\
**Post date:** [26 August 2021 22:02 UTC](https://discourse.nodered.org/t/serial-node-strangeness/50232/3 "2021-08-26T22:02:21Z")

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Interesting. Both of my serial port nodes are configured to talk to the same device (ttyUSB0). That is one of the most perplexing things to me, that one would work and the other would not.

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**Author:** ![TotallyInformation](https://sea2.discourse-cdn.com/flex026/user_avatar/discourse.nodered.org/totallyinformation/32/31_2.png) [@TotallyInformation](https://discourse.nodered.org/u/TotallyInformation)\
**Post date:** [26 August 2021 22:04 UTC](https://discourse.nodered.org/t/serial-node-strangeness/50232/4 "2021-08-26T22:04:25Z")

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Serial ports are usually opend exclusively so one will open and lock it, the other will fail. This is a pretty typical pattern.

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<div class="post-metadata">

**Author:** ![Steve-Mcl](https://sea2.discourse-cdn.com/flex026/user_avatar/discourse.nodered.org/steve-mcl/32/4826_2.png) [@Steve-Mcl](https://discourse.nodered.org/u/Steve-Mcl)\
**Post date:** [26 August 2021 22:17 UTC](https://discourse.nodered.org/t/serial-node-strangeness/50232/5 "2021-08-26T22:17:46Z")

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How many serial config nodes do you see if you click the drop-down config node list?

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<div class="post-metadata">

**Author:** ![SteveDonie](https://sea2.discourse-cdn.com/flex026/user_avatar/discourse.nodered.org/stevedonie/32/5212_2.png) [@SteveDonie](https://discourse.nodered.org/u/SteveDonie)\
**Post date:** [27 August 2021 14:57 UTC](https://discourse.nodered.org/t/serial-node-strangeness/50232/6 "2021-08-27T14:57:56Z")

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There is just one serial config node, used by the two different nodes (one serial-in and one serial-out).

 ![Screen Shot 2021-08-27 at 9.53.30 AM](https://us1.discourse-cdn.com/flex026/uploads/nodered/original/3X/4/7/47bbd5507c15ed415afb10130665354e59818c65.jpeg)

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<div class="post-metadata">

**Author:** ![SteveDonie](https://sea2.discourse-cdn.com/flex026/user_avatar/discourse.nodered.org/stevedonie/32/5212_2.png) [@SteveDonie](https://discourse.nodered.org/u/SteveDonie)\
**Post date:** [27 August 2021 15:00 UTC](https://discourse.nodered.org/t/serial-node-strangeness/50232/7 "2021-08-27T15:00:19Z")

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Thanks - I replied below that I see there is one "serial configuration node" that is used by both the serial-in node and the serial-out node. This exact flow has worked for over a month, and nothing that I know of has changed, which is why this is extra strange.

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<div class="post-metadata">

**Author:** ![system](https://us1.discourse-cdn.com/flex026/uploads/nodered/original/1X/d073cd938eafa2e558d7c2cd59003b3ef4963033.png) [@system](https://discourse.nodered.org/u/system)\
**Post date:** [26 October 2021 15:01 UTC](https://discourse.nodered.org/t/serial-node-strangeness/50232/8 "2021-10-26T15:01:10Z")

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