Serial port not working?

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I made a program that sends out data to my arduino which detects what was sent and then turns on the correct pin according to what key is pressed.

When using the arduino software from my windows computer the arduino sketch works fine, I can make each pin turn on and off by sending either W A S Or D.

When sending via node the RX light on the arduino flashes but nothing else happens.

Can anyone help?

Node.js program:

var httpServer = require('http').createServer(function(req, response){ /* Serve your static files */ })

var nowjs = require("now");
var everyone = nowjs.initialize(httpServer); = function(msg){

var SerialPort = require('serialport2').SerialPort;
var assert = require('assert');

var portName;

if (process.platform == 'win32') {
  portName = 'COM4';
} else if (process.platform == 'darwin') {
  portName = '/dev/cu.usbserial-A800eFN5';
} else {
  portName = '/dev/ttyUSB0';

var readData = '';
var sp = new SerialPort();

sp.on('close', function (err) {
  console.log('port closed');

sp.on('error', function (err) {
  console.error("error", err);

sp.on('open', function () {
  console.log('port opened... Press reset on the Arduino.');
});, {
  baudRate: 9600,
  dataBits: 8,
  parity: 'none',
  stopBits: 1,
  flowControl: false
}); = function() {
} = function() {
} = function() {
} = function() {

sp.on('data', function(data) {

Arduino Program:

void setup(){
  //Set all the pins we need to output pins
  pinMode(8, OUTPUT);
  pinMode(9, OUTPUT);
  pinMode(10, OUTPUT);
  pinMode(11, OUTPUT);

void loop (){
  if (Serial.available() > 0) {

    //read serial as a character
    char ser =;
    //NOTE because the serial is read as "char" and not "int", the read value must be compared to character numbers
    //hence the quotes around the numbers in the case statement
    switch (ser) {
      case 'w':
      case 's':
      case 'a':
      case 'q':
      case 'd':
      case 'e':

void move(int pin){
  digitalWrite(pin, HIGH);
  digitalWrite(pin, LOW);

I recently dabbled into this. The Arduino automatically resets when it receives serial communication from most things other than the Arduino IDE. This is why you can send from the IDE but not node.js.

I have an Uno and put a capacitor between Reset and Ground.Here's a page with some good info on the subject. Good luck.

Serial Port Configuration, parameters, which includes baud rate, parity, number of data bits, and number of stop bits. A software driver may result in a non-working serial port. If this driver is not installed properly or is not compatible with a serial port, it may cease to perform. Re-installing the affected drivers can help a user overcome this problem. In addition, a user may be able to alter the serial port settings to ensure this issue is fully resolved.

On the capacitor and reset issue... There is a small capacitor between one of the serial control lines and reset on the Arduino in the later models. This capacitor causes the Arduino to reset when the port is opened but otherwise does not interfere with normal serial operation.

This reset trick allows the code upload to reset the Arduino as part of the upload process. When the Arduino starts up the code boot loader runs first for a short time before the loaded code runs.

The upload process is: Reset the Arduino which starts the boot loader, start the upload process in the Arduino IDE, establish communications, upload, then run the loaded code. When the Arduino starts up it waits for uploads for a short period of time, if none are received, it moves on to running the code.

I find this very useful as it allows us to effectively reset the Arduino just by closing and opening the port. In the old Arduino's, without this capacitor, you had to press the reset button at the right time to get the code to upload. And the timing was such that the Arduino spent much more time waiting before it started with the uploaded code.

In the problem described here, I do not believe he was having any troubles due to the reset trick used. It should have had only the effect of resetting the Arduino when he opened the serial port, and from the looks of his information, this is a desired side-effect.

6 Common Communication Problems Involving Serial Connections, If your USB to RS-232 cable does not appear in the list of available COM ports, check that the USB driver is properly installed. #5 - COM Port  When the COM and LPT ports do not appear in your Windows 10 Device Manager your ability to perform your work is negatively impacted. There is a way to resolve this annoying problem in a manner that will prevent it from recurring. The solution is to install the aforementioned Virtual COM Port Driver from Eltima. This application allows the

I use node on a daily basis to send actions to my Arduino via usb or via bt and it works great in both cases. I think your problem comes from sending letters. You should send a buffer instead, with the ascii value of the letter, just like that:


also, for this, I think you would be better with some "logic" interface, with data headers, number of actions, stuff like that. It is no required for you but it will make your code more robust and easier to modify in the future.

Here is an example of how I do it. First, Node:

var dataHeader = 0x0f, //beginning of the data stream, very useful if you intend to send a batch of actions
myFirstAction = 0x01,
mySecondAction = 0x02,
myThirdAction = 0x03;

You then call them like you did: = function() {

    sp.write(Buffer([0x03])); // this is the number of actions for the Arduino code


This way it is easy on the Arduino to the data: (Note that you need to define data header and data footer somewhere)

void readCommands(){
    while(Serial.available() > 0){

        // Read first byte of stream.
        uint8_t numberOfActions;
        uint8_t recievedByte =;

        // If first byte is equal to dataHeader, lets do
        if(recievedByte == DATA_HEADER){

            // Get the number of actions to execute
            numberOfActions =;


            // Execute each actions
            for (uint8_t i = 0 ; i < numberOfActions ; i++){

                // Get action type
                actionType =;

                if(actionType == 0x01){
                    // do you first action
                else if(actionType == 0x02{
                    // do your second action
                else if(actionType == 0x03){
                    // do your third action

I hope I'm clear and I hope it helps! Cheers!

Everything is hooked up but nothing is working. What should I do , When you troubleshoot issues with a serial device, there are some quick tests that you can complete to rule out potential problems. You can test to make sure  Parallel and serial ports not working in Windows 10 (Version 1511) Since the 1511 update myself and my customers have problems with devices connected to COMx and LPTx ports. After a search I found a solution by disabling the ports and then re-enabling them and a script to run at boot time to automated the process.

In my case the issue was the reset, but that the serial port was opened - but not available for write until the reset has finished. Putting a 3s delay before writing to the port fixed the issue. Writing ASCII was not an issue.

Serial port troubleshooting, It will take less time to fix a COM port error if you know what to look for. In this article, we'll tell you  A simple way to be certain the port is correct is by re-uploading the sketch from the same IDE that is used to open the Serial Monitor. STEP 2: Verify the Serial Monitor on the computer and the Serial Port on the Arduino are set to the same data rate. The data rate is often referred to as the baud rate.

COM port error: basic information about serial port debug technology, The way to resolve this issue is through the use of Windows virtual serial ports. It can be very frustrating to query your Device Manager with the  In the old days of personal computers, one of the primary connections available was the RS-232 serial port. Apart from the parallel port, it was the primary means to connect an external device. The connector was reduced from a 25-pin connector to a 9-pin connector, but RS-232 ports remained present on every computer for many years.

COM ports Windows 10: fix any COM port issues , Troubleshooting a serial COM port connection How To Fix USB Ports Not Working or Not Duration: 2:00 Posted: May 8, 2014 If you quickly and repeatedly insert and remove a USB device, the USB port may stop responding. When the port is in this state, it no longer recognizes any USB device, and the USB device will not work. This article helps you fix the problem.

Troubleshooting a serial COM port connection, To see if this is the problem (and hopefully fix it), try changing the assigned COM port. Go to Device Manager > Ports (COM & LPT) > mbed Serial  Many parallel scanners and multifunction devices will not work unless mode is set to Extended Capabilities Port (ECP) or Bi-directional. Press the F10 key to save the settings and exit. Connect a serial or parallel device to test the serial or parallel port. If the serial or parallel device fails, go to the next step.

  • Update, By the looks of it the arduino is not detecting the serial port as available. I don't know if that helps.
  • My first thought is that the serial port is detected and working (due to the flashing led). My guess is on the sending end. Try googling "ComEmulDrv3". It should let you set up a virtual comport allowing you to verify what your sending. Things to look for include character encoding and whitespace.
  • Hmm, but the examples even ask for you to reboot the arduino :S
  • In order for the IDE to upload code, it has to be able to reboot the Arduino. So, whenever you do an upload, you have to remove the capacitor, let it upload, then replace the capacitor for serial to work properly (without restarting). Your code looks good, especially if it works properly when sending serial data from the IDE.
  • Hmm, but when using the IDE it sends, when using node It don't. At the moment I'm waiting for a Logic Level Converter so I can use it with the serial ports on my Raspberry Pi. If it don't work when I do that then I will post again ;)
  • That's perfectly correct, without the capacitor/resistor, you have few choices for serial communication. I'm quite sure that your node.JST app will work once you try adding this.
  • Visual Micro, I can confirm your remark about disabling DTR in C# and that works with Arduino. For node.js I found this article where they initialize the serialport with 'flowControl: false' I expect this should not send any signal on the DTR/DTS pins: serialPort = new SerialPort(portName, { baudrate: 9600, dataBits: 8, parity: 'none', stopBits: 1, flowControl: false });