nodejs serialport write issues?

Question

I am using the nodejs serialport module (https://npmjs.org/package/serialport) and I am having issues when I write to the serial port.

If I simply write to the port as shown below, the serial device never gets the command.

var serialport = require("serialport");
var sp = new serialport.SerialPort(serialPortPath);
sp.write("SYST:ADDR?\n");

However, if I use a setTimeout as shown below, then it seems to work?

var serialport = require("serialport");
var sp = new serialport.SerialPort(serialPortPath);
setTimeout(function(){sp.write("SYST:ADDR?\n")},1000);

FYI, the "serialPortPath" is set elsewhere in the code.

I am not sure what is going on... any ideas?

score 1 · Answer 1 · answered Jan 24 '13 at 03:06

I think I got it figured out from the github (https://github.com/voodootikigod/node-serialport page... basically it looks like I was missing the "open" event as shown below:

serialPort.on("open", function () {
  console.log("open");
  serialPort.on("data", function(data) {
    console.log("data received: " + data);
  });  
  serialPort.write("SYST:ADDR?\n", function(err, results) {
    console.log("err: " + err);
    console.log("results: " + results);
  });  
});

score 1 · Answer 2 · answered Mar 31 '17 at 20:45

Here is another approach which works very well and allows for dynamic addressing of a specific serial device. In my case I am only interested in connecting to the Numato device connected to our integrated system which is why I have the conditional logic in the list callback.

 exports.testSerial = function(data) {
    serialPort.list(function(err, ports) {

      var port = {};

      for(var i = 0; i < ports.length; i++) {
        try {
          if(typeof ports[i].manufacturer != 'undefined' && ports[i].manufacturer.includes("Numato")) {
            port = ports[i];
          }
        } catch(err) {
          console.dir(err);
        }
      }

      // the port will be opened via the constructor of this call
      var numato = new serial(port.comName, {baudrate : 19200}, function(err) {
        if(err) {
          return console.dir(err);
        }

        // by having the write call within the callback you can access it directly w/o using .on()
        numato.write('relay ' + data.state + ' ' + data.channel + '\r', function(err) {
          if(err) {
            console.dir('error writing');
            console.dir(err);
          }
          console.dir('serial message written');
          numato.close();
        });
      });

      return true;

    });
 }

Hope this helps someone in the future! For reference this is with library version 4.0.7.

nodejs serialport write issues?

2 Answers2