Creating HMIs With Unserver - Part 2: Indicators

Unserver on tutorial -


This tutorial demonstrates how to create a level indicator visualization integrated with Unserver:


The full full code for this article is available on Github.

PLC Program API

The PLC is measuring the amounts of liquid in two tanks. The values of the tanks are stored as 32-bit floating point numbers at HR200 and HR202.

Our HMI has to continuosly fetch and display those two values.

Unserver Configuration

Let's start with tag configuration.


        "name": "tank-levels", "device": "plc1", 
        "polling": {"enabled":true, "frequency": 2 },
        "properties": [
            { "name": "tank1", "address":"HR200", "type": "numeric", "raw": "float32" },
            { "name": "tank2", "address":"HR202", "type": "numeric", "raw": "float32" }


Here we have created one tag - tank-levels with tho properties - tank1 and tank2.

When a property is mapped as a float32, Unserver will read two consecutive registers to get 32 bits of data and convert them to a 32-bit floating poing number.

For instance, to manipulate tank1 property Unserver will use both HR200 and HR201.

After modifying tags.json we can run Unserver and see that everything is working by calling the tag from the browser:

Calling Unserver directly from the browser

The tag's value is being returned, which means the configuration is correct.

Web App Development

We will be using the following libraries to simplify development:


The following code creates two indicator components on the page, each bound to a corresponding property of the Vue App:


<div class="pure-u-1-5">
    <div class="center"><h2>TANK LEVELS</h2></div>
    <div class="pure-g" id="root">
        <div class="pure-u-1-2 center">
            <indicator v-bind:value="tank1"></indicator>
            <div>Tank 1</div>
        <div class="pure-u-1-2 center">
            <indicator v-bind:value="tank2"></indicator>
            <div>Tank 2</div>


The Vue app is really simple - it only has two properties:


var app = new Vue({

The following code creates an instance of Unserver client and subscribes to property updates:


var u = new Unserver("");

u.watchProperty('tank-levels.tank1', function(value){
    app.tank1 = value;

u.watchProperty('tank-levels.tank2', function(value){
    app.tank2 = value;


Every time a new property value is received, a corresponding app property is updated.

The indicator component found in index.js contains the code for rendering the visual representation of the value from app.tank1 and app.tank2.

Testing the App

We can now open index.html in a browser and see our live visualization.

To test that everyting is working correctly, let's try to update PLC data using Unserver API:

u.setProperty('tank-levels.tank1', 34.5);
u.setProperty('tank-levels.tank1', 14.2);

As you can see below, the app is responding correctly:


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