Communication with an Arduino via Serial

The Serial protocol is currently not supported directly in the browser, but there is an easy workaround to use your Arduino, e.g. to control a cables patch using a sensor, in cables.

First of all you need to connect an Arduino via USB and upload a basic patch which just outputs the numbers 0–9 via Serial:

void setup() {

void loop() {
  for(int i=0; i<10; i++) {

If you open the Arduino Serial monitor (by pressing cmd + shift + m) you should see the following:

Now we need to download serial-port-json-server, a little helper tool to send the Serial data to your cables patch. Go to the release page, find the right version for your operating system and download it. If there is none for the latest release, just pick the release prior to that.

Once downloaded extract the zip-file, go into the extracted folder and you should see a file called serial-port-json-server / serial-port-json-server.exe. Run this file in your Terminal / command prompt. On mac you do this by opening up Terminal-app, then cd into the directory, e.g.:

cd /Users/carolin/Downloads/serial-port-json-server-1.94_macosx

Then execute the binary by running:


You should now see an output like this:

2018/04/10 14:43:31 main.go:97: Version:1.94
2018/04/10 14:43:31 main.go:104: Hostname: Carolin-MacBook-Pro.local
2018/04/10 14:43:31 main.go:110: Garbage collection is on using Standard mode, meaning we just let Golang determine when to garbage collect.
2018/04/10 14:43:31 main.go:137: You can enter verbose mode to see all logging by starting with the -v command line switch.
2018/04/10 14:43:31 main.go:152: Your serial ports:
2018/04/10 14:43:31 main.go:159:     {/dev/cu.Bluetooth-Incoming-Port cu.Bluetooth-Incoming-Port []      }
2018/04/10 14:43:31 main.go:159:     {/dev/cu.usbmodem1421 cu.usbmodem1421 []      }
2018/04/10 14:43:31 main.go:159:     {/dev/tty.Bluetooth-Incoming-Port tty.Bluetooth-Incoming-Port []      }
2018/04/10 14:43:31 main.go:159:     {/dev/tty.usbmodem1421 tty.usbmodem1421 []      }

We now have a local websocket server running which we can use to create a bridge between the Arduino and cables!

Now open a new tab in your browser and go to http://localhost:8989/, this is the interface to the server we just started. The output looks a bit cryptic, but we won’t spend much time here…

Before we can access the Serial data, we need to connect to the Serial device. In the input field on the bottom enter list and press Send. This will list all available serial devices. The output should look something like this:

{ "SerialPorts": [ { "Name": "/dev/cu.Bluetooth-Incoming-Port", "Friendly": "cu.Bluetooth-Incoming-Port", "SerialNumber": "", "DeviceClass": "", "IsOpen": false, "IsPrimary": false, "RelatedNames": null, "Baud": 0, "BufferAlgorithm": "", "AvailableBufferAlgorithms": [ "default", "timed", "nodemcu", "tinyg", "tinyg_old", "tinyg_linemode", "tinyg_tidmode", "tinygg2", "grbl", "marlin" ], "Ver": 1.94, "UsbVid": "", "UsbPid": "", "FeedRateOverride": 0 }, { "Name": "/dev/cu.usbmodem1421", "Friendly": "cu.usbmodem1421", "SerialNumber": "", "DeviceClass": "", "IsOpen": false, "IsPrimary": false, "RelatedNames": null, "Baud": 0, "BufferAlgorithm": "", "AvailableBufferAlgorithms": [ "default", "timed", "nodemcu", "tinyg", "tinyg_old", "tinyg_linemode", "tinyg_tidmode", "tinygg2", "grbl", "marlin" ], "Ver": 1.94, "UsbVid": "", "UsbPid": "", "FeedRateOverride": 0 }, { "Name": "/dev/tty.Bluetooth-Incoming-Port", "Friendly": "tty.Bluetooth-Incoming-Port", "SerialNumber": "", "DeviceClass": "", "IsOpen": false, "IsPrimary": false, "RelatedNames": null, "Baud": 0, "BufferAlgorithm": "", "AvailableBufferAlgorithms": [ "default", "timed", "nodemcu", "tinyg", "tinyg_old", "tinyg_linemode", "tinyg_tidmode", "tinygg2", "grbl", "marlin" ], "Ver": 1.94, "UsbVid": "", "UsbPid": "", "FeedRateOverride": 0 }, { "Name": "/dev/tty.usbmodem1421", "Friendly": "tty.usbmodem1421", "SerialNumber": "", "DeviceClass": "", "IsOpen": false, "IsPrimary": false, "RelatedNames": null, "Baud": 0, "BufferAlgorithm": "", "AvailableBufferAlgorithms": [ "default", "timed", "nodemcu", "tinyg", "tinyg_old", "tinyg_linemode", "tinyg_tidmode", "tinygg2", "grbl", "marlin" ], "Ver": 1.94, "UsbVid": "", "UsbPid": "", "FeedRateOverride": 0 } ] }

Here we need to find the name of our Arduino (serial device), in my case this is /dev/cu.usbmodem1421 . (this name also shows up in the Arduino app: Tools —> Port).

Now that we know the name of our Serial device enter the following command and press Send:

open /dev/cu.usbmodem1421 9600

This opens a Serial connection to your Arduino with the baud-rate 9600 (the same we used in our Arduino sketch). You should now see a (nearly) identical output to the Arduino Serial Monitor:

Great, let’s head over to cables, create a new patch and add the WebSocket op and enter ws://localhost:8989/ws as Url.

Once entered the Connected port should change to true.

If you now click on the little magnifier icon next to the Result port you can inspect the last message we received:

Press Update and the D-property should change.

To make use of the incoming data we need to extract the value. Connect a GetValue op to the Result port and enter D as the key:

From here on you can use the Result value however you like. In the Arduino Serial Tutorial patch you can see how the data from the Arduino changes the size of the circle.

Now go on and build some crazy things with Arduino + cables :)

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