# How to send command to Arduino through serial commend?

**URL:** <https://discourse.nodered.org/t/how-to-send-command-to-arduino-through-serial-commend/57096>\
**Category:** General\
**Created:** [23 January 2022 15:03 UTC](https://discourse.nodered.org/t/how-to-send-command-to-arduino-through-serial-commend/57096 "2022-01-23T15:03:36Z")\
**Posts on this page:** 6\
**Page:** 1

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**Author:** ![51fei](https://sea2.discourse-cdn.com/flex026/user_avatar/discourse.nodered.org/51fei/32/54820_2.png) [@51fei](https://discourse.nodered.org/u/51fei)\
**Post date:** [23 January 2022 15:03 UTC](https://discourse.nodered.org/t/how-to-send-command-to-arduino-through-serial-commend/57096/1 "2022-01-23T15:03:36Z")

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I want to use Node-RED: inject node to send commands to Arduino, Below is the code I wrote, but it did not work. Does anyone know how to write? Thank you.

```auto
void messageReceived () {
   if (payload = 0) 
   {
     Serial.println("open");
     digitalWrite(pump_in1_sol_A, HIGH); 
     digitalWrite(pump_in2_sol_A, LOW); 
   } 
   else if (payload = 1) 
   {
     Serial.println("closed");
     digitalWrite(pump_in1_sol_A, LOW); 
     digitalWrite(pump_in2_sol_A, LOW);  
   }
}

```

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**Author:** ![jbudd](https://avatars.discourse-cdn.com/v4/letter/j/5f8ce5/32.png) [@jbudd](https://discourse.nodered.org/u/jbudd)\
**Post date:** [23 January 2022 15:23 UTC](https://discourse.nodered.org/t/how-to-send-command-to-arduino-through-serial-commend/57096/2 "2022-01-23T15:23:02Z")

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Does the code you posted run on the Arduino?  
The statement **if (payload = 0)** looks wrong. You are assigning a value to payload, not testing the current value.

There is a [Serial i/o node](https://flows.nodered.org/node/node-red-node-serialport) which sends msg.payload to the serial port. Are you using that?  
 ![Untitled 1](https://us1.discourse-cdn.com/flex026/uploads/nodered/original/3X/8/b/8b5498df3096afc66adb5f45e5b2f6aa535cfd3f.jpeg)

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**Author:** ![zenofmud](https://sea2.discourse-cdn.com/flex026/user_avatar/discourse.nodered.org/zenofmud/32/316_2.png) [@zenofmud](https://discourse.nodered.org/u/zenofmud)\
**Post date:** [23 January 2022 16:27 UTC](https://discourse.nodered.org/t/how-to-send-command-to-arduino-through-serial-commend/57096/3 "2022-01-23T16:27:17Z")

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@51fei

> [@jbudd](#):
>
> if (payload = 0)

You should go read this: [if - Arduino Reference](https://www.arduino.cc/reference/en/language/structure/control-structure/if/)

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<div class="post-metadata">

**Author:** ![MaddyP](https://sea2.discourse-cdn.com/flex026/user_avatar/discourse.nodered.org/maddyp/32/53046_2.png) [@MaddyP](https://discourse.nodered.org/u/MaddyP)\
**Post date:** [23 January 2022 18:39 UTC](https://discourse.nodered.org/t/how-to-send-command-to-arduino-through-serial-commend/57096/4 "2022-01-23T18:39:41Z")

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Should be:

if (payload == 0)

not

if (payload = 0)

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<div class="post-metadata">

**Author:** ![51fei](https://sea2.discourse-cdn.com/flex026/user_avatar/discourse.nodered.org/51fei/32/54820_2.png) [@51fei](https://discourse.nodered.org/u/51fei)\
**Post date:** [25 January 2022 11:58 UTC](https://discourse.nodered.org/t/how-to-send-command-to-arduino-through-serial-commend/57096/5 "2022-01-25T11:58:44Z")

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Thank you, I had solved the problem.

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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:** [26 March 2022 11:58 UTC](https://discourse.nodered.org/t/how-to-send-command-to-arduino-through-serial-commend/57096/6 "2022-03-26T11:58:52Z")

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