# Create an LCD screen with the HTML Canvas

This example shows how to create an LCD screen on a dashboard using the HTML Canvas widget.

#### HTML:

```html
<div id="image_background">
<p>Last value:</p>
<span id="image_background_text">No data</span>
</div>
```

#### CSS:

```css
@import url('https://fonts.googleapis.com/css?family=VT323');

#image_background {
background: url('https://i.imgur.com/uuYygjz.png') 0 / contain no-repeat;
font-family: "VT323";
font-size: 25px;
letter-spacing: 10.5px;
height: 220px;
width: 450px;
}

#image_background p, #image_background_text {
margin: 0;
left: 75px;
position: absolute;
}

#image_background p {
top: 88px;
font-size: 25px !important;
}

#image_background_text {
top: 121px;
}

```

#### JavaScript:

In the following code, set `VAR_ID` to the variable ID to display:

```javascript
var bg = document.getElementById("image_background");
var text = document.getElementById("image_background_text");
var lastValue = null;
var TOKEN = ubidots.token;
var VAR_ID = "variable-id";

setInterval(function () { getLastValue(VAR_ID, TOKEN); }, 2000);

function makeHttpRequest(method, url, headers, payload) {
  return new Promise(function (resolve, reject) {
    var options = {
      method: method,
      headers: headers,
    };

    if (payload) {
      options.body = JSON.stringify(payload);
    }

    fetch(url, options)
      .then(function (response) {
        if (!response.ok) {
          throw new Error(response.statusText);
        }
        return response.json();
      })
      .then(function (data) {
        resolve(data);
      })
      .catch(function (error) {
        reject(error);
      });
  });
}

function changeImage(value) {
  var choose = "normal";
  var background = {
    blue: "https://i.imgur.com/ZE0W7Yx.png",
    normal: "https://i.imgur.com/uuYygjz.png",
    yellow: "https://i.imgur.com/RHvDkUE.png",
  };
  if (value <= 30) {
    choose = "blue";
    bg.style.color = "white";
  } else if (value > 30 && value <= 70) {
    choose = "yellow";
    bg.style.color = "white";
  }
  bg.style.background = "url(" + background[choose] + ") 0 / contain no-repeat";
}

function getLastValue(variableId, token) {
  var url =
    "https://industrial.api.ubidots.com/api/v1.6/variables/" +
    variableId +
    "/values";
  var headers = {
    "X-Auth-Token": token,
    "Content-Type": "application/json",
  };

  makeHttpRequest("GET", url + "?page_size=1", headers)
    .then(function (res) {
      if (lastValue === null || res.results[0].value !== lastValue) {
        text.textContent = res.results[0].value;
        lastValue = res.results[0].value;
        changeImage(lastValue);
      }
    })
    .catch(function (error) {
      console.error(error);
    });
}
```

Once you save the settings, it looks like this:

<figure><img src="/files/AZgdJUoZC48JB3I3KqEE" alt="" width="563"><figcaption></figcaption></figure>

### Adjusting the screen's contrast

Update the HTML to:

```html
<div id="image_background">

<img id="display_background" src="https://i.imgur.com/meoKhMG.png" />

<p>Last value:</p>
<span id="image_background_text">No data</span>
</div>
```

Update the CSS to:

```css
@import url('https://fonts.googleapis.com/css?family=VT323');

#image_background {
background: url('https://i.imgur.com/ehNdUxY.png') 0 / contain no-repeat;
font-family: "VT323";
font-size: 25px;
letter-spacing: 10.5px;
height: 220px;
width: 450px;
}

#image_background p, #image_background_text {
margin: 0;
left: 75px;
position: absolute;
}

#image_background p {
top: 88px;
font-size: 25px !important;
}

#image_background_text {
top: 121px;
}

#display_background {
height: 94px;
position: absolute;
top: 70px;
left: 52px;
pointer-events: none;
}
```

Update the JavaScript to:

```javascript
var bg = document.getElementById("display_background");
var text = document.getElementById("image_background_text");
var lastValue = null;
var lastContrast = null;
var TOKEN = ubidots.token;
var VAR_ID_LV = "id-of-variable-to-be-displayed";
var VAR_ID_CONTRAST = "id-of-contrast-variable";
var scale = d3.scaleLinear().range([0, 4]).domain([0, 1023]);


setInterval(function () {
    // Get LCD Screen last value
    getLastValue(VAR_ID_LV, TOKEN, function (res) {
      var value = null;
      try {
        value = res.results[0].value;
      } catch (e) {
        console.log("No data");
      }
      if (
        (lastValue === null || value !== lastValue) &&
        value !== null
      ) {
        text.textContent = value;
        lastValue = value;
      }
    });

    // Get LCD Screen contrast
    getLastValue(VAR_ID_CONTRAST, TOKEN, function (res) {
      var value = null;
      try {
        value = res.results[0].value;
      } catch (e) {
        console.log("No data");
      }
      if (
        (lastContrast === null || value !== lastContrast) &&
        value !== null
      ) {
        bg.style.filter = "contrast(" + scale(value) + ")";
        lastContrast = value;
      }
    });
  }, 2000);


function makeHttpRequest(method, url, headers, payload) {
  return new Promise(function (resolve, reject) {
    var options = {
      method: method,
      headers: headers,
    };

    if (payload) {
      options.body = JSON.stringify(payload);
    }

    fetch(url, options)
      .then(function (response) {
        if (!response.ok) {
          throw new Error(response.statusText);
        }
        return response.json();
      })
      .then(function (data) {
        resolve(data);
      })
      .catch(function (error) {
        reject(error);
      });
  });
}

function getLastValue(variableId, token, cb) {
  var url =
    "https://industrial.api.ubidots.com/api/v1.6/variables/" +
    variableId +
    "/values";
  var headers = {
    "X-Auth-Token": token,
    "Content-Type": "application/json",
  };

  makeHttpRequest("GET", url + "?page_size=1", headers)
    .then(function (res) {
      if (typeof cb === "function") cb(res);
    })
    .catch(function (error) {
      console.error(error);
    });
}

```

Lastly, add the third-party library required for this implementation:

```
https://cdnjs.cloudflare.com/ajax/libs/d3/4.9.0/d3.min.js
```

Result:

<figure><img src="/files/Fxui4eRZCvarYUqZJQjJ" alt=""><figcaption></figcaption></figure>


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