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Arduino - Live Chart

This data server charts data logged from a USB-connected Arduino, or data POSTed from an Ethernet- or Wi-Fi- capable Arduino over the network.

The Arduino sends data in JSON. For a USB-connected Arduino, you can use any Arduino-side program to send the data; one convenient way is to use Bitlash; see below. You can find out more about Bitlash at

For a network-connected Arduino you'll need to write a client to make a simple POST request via your network adapter; see way below for details.

Pre-install Requirements

Node.js and git

You need to install node.js ( and git (

This package uses the node-serial module, which requires you have some tools on your system to compile a driver. See this link for more:

Get the arduino-livechart code

Open a terminal window and enter the commands below to install the web chart server:

$ git clone
$ cd arduino-livechart
$ npm install
$ node index.js 

Now open a web browser on http://localhost:3000 and you should see the chart page.

If you would prefer to start the web server on a different port:

$ node index.js -p 8080

To stop the server, type Control-] in its terminal window.

The server will try to guess the serial port to which your Arduino is connected. You can override the automatic port detection and specify a serial port with the -s flag:

$ node index.js -s /dev/tty.USB.abcdef

On the Arduino: Install

You need to install the Bitlash library ( Don't forget to restart the Arduino software.

Once the Bitlash software is installed, you can install the bitlash demo on your Arduino via:

File -> Examples -> bitlash -> demo
File -> Upload

Connect to your arduino with whatever serial monitor you usually use and you should be talking to Bitlash. I use "bitty.js":

On the Arduino: Testing the Arduino setup

The basic idea is to set up Bitlash to print a little JSON record for each data snapshot, one record per line. (Non-JSON lines are ignored.)

A quick demonstration example: generate random data for a0 and a1.

Define these functions in Bitlash; you can copy and paste from here (minus the '>'):

> function logrand { printf("{\"time\":%d,\"a0\":%d,\"a1\":%d}\n", millis, random(100), random(100));};

Go refresh the chart in your browser and you should see three data points.

To log data every second when the arduino boots:

> function startup {run logrand,1000}
> boot

Let it run a while and refresh the chart.

Congratulations, you have a working data collection and charting system.

Charting different data

The charting program detects whatever fields you have present in the log records, so you could log a different set of values like this to see a different chart:

> function log {printf("{\"time\":%d,\"a0\":%d,\"count\:%d,\"switch\":%d}", millis, a0, c, d3);}

The data format is JSON, which unfortunately contains lots of quote characters which need to be escaped. The printf() above produces output like this:


The "time" field is required. Anything else you provide is plotted against time.

Integrating additional Arduinos

You can also POST data to the PC running the live chart from any net-capable Arduino, such as an Arduino with an Ethernet or Wi-Fi sheild.

The POST url is http:///json. The POST Content-Type header should be set to 'application/json'. The POST body should contain the JSON data to be logged, like the example above.

This curl command sends a test POST:

curl -X POST -H 'Content-Type:application/json' -d '{"time":200,"a0":22,"a1":23}' localhost:3000/json


Generates a D3 chart of data logged from a USB-connected Arduino







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