# Arduino port number on RPI
**URL:** https://discourse.nodered.org/t/arduino-port-number-on-rpi/49387
**Category:** General
**Created:** [5 August 2021 15:53 UTC](https://discourse.nodered.org/t/arduino-port-number-on-rpi/49387 "2021-08-05T15:53:16Z")
**Posts on this page:** 3
**Page:** 1
### Author:  [@mustafa](https://discourse.nodered.org/u/mustafa)
#### Post date: [5 August 2021 15:53 UTC](https://discourse.nodered.org/t/arduino-port-number-on-rpi/49387/1 "2021-08-05T15:53:16Z")
Hi
I have connected arduino uno to RPI3 but there is something strange which is the port number that appear on node red arduio node in or out is changed each time after switching power OFF/ON of RPI3
sometimes I find it as /dev/ttyACM0 and after few minutes I find it as /dev/ttyACM1 or it changed between them at changing the USB connection on RPI when I didn't got any response from Arduino even at selecting the connected port for the command ls /dev/tty\*
or also when I connect two Arduinos uno on appear as /dev/ttyACM1 and the second is appear as /dev/ttyACM2
but when I did a simple switch node ui to give ON command to the Arduino out node and select the out no.13 the response will be only one Arduino will operate for ON/OFF LED and the other Arduino is not responding
I tried many times in changing the port number but not work all the time
simple code is
```auto
[
{
"id": "f76d4094de123157",
"type": "ui_switch",
"z": "ed4e4a187f00a929",
"name": "",
"label": "switch1",
"tooltip": "",
"group": "b3442ac2.24b5b8",
"order": 2,
"width": 0,
"height": 0,
"passthru": true,
"decouple": "false",
"topic": "topic",
"topicType": "msg",
"style": "",
"onvalue": "true",
"onvalueType": "bool",
"onicon": "",
"oncolor": "",
"offvalue": "false",
"offvalueType": "bool",
"officon": "",
"offcolor": "",
"animate": false,
"x": 280,
"y": 180,
"wires": [
[
"9423fe2b3e59749a"
]
]
},
{
"id": "9423fe2b3e59749a",
"type": "arduino out",
"z": "ed4e4a187f00a929",
"name": "",
"pin": "13",
"state": "OUTPUT",
"arduino": "599bf8e7eb96c8b9",
"x": 620,
"y": 180,
"wires": []
},
{
"id": "b3442ac2.24b5b8",
"type": "ui_group",
"name": "Mustafa",
"tab": "fc4b1c12.afee3",
"order": 1,
"disp": false,
"width": "8",
"collapse": false
},
{
"id": "599bf8e7eb96c8b9",
"type": "arduino-board",
"device": "/dev/ttyACM0"
},
{
"id": "fc4b1c12.afee3",
"type": "ui_tab",
"name": "Home",
"icon": "my dash",
"order": 2,
"disabled": false,
"hidden": false
}
]
```
any advice please
---
### Author:  [@Gunner](https://discourse.nodered.org/u/Gunner)
#### Post date: [5 August 2021 18:30 UTC](https://discourse.nodered.org/t/arduino-port-number-on-rpi/49387/2 "2021-08-05T18:30:20Z")
This is more an RPi issue than Node-Red
Try this.
[https://www.raspberrypi.org/forums/viewtopic.php?t=217511](https://www.raspberrypi.org/forums/viewtopic.php?t=217511)
And Google for more if needed. It is a common thing with RPi
---
### Author:  [@system](https://discourse.nodered.org/u/system)
#### Post date: [4 October 2021 18:31 UTC](https://discourse.nodered.org/t/arduino-port-number-on-rpi/49387/3 "2021-10-04T18:31:06Z")
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