# NFC Reader

The [NFC Reader](https://www.tinkerforge.com/de/doc/Hardware/Bricklets/NFC.html) can be thought of as a sensor, but it has some particularities that we need to address. In this article, we assume you have successfully initialized the devices with the [Tinkerforge Device Manager](https://iot.datalit.de/2-internet-of-things/iot-in-our-apps/connect-to-devices/the-tinkerforge-device-manager), and you stored all connected devices on a global variable `devices`. We also declared a global variable called `nfcReader`. 

## Getting the NFC reader

Next, we need to know the [device identifier](https://www.tinkerforge.com/de/doc/Software/Device_Identifier.html), which **286**:

```javascript
// Get the NFC reader via its device identifer
nfcReader = devices.getDeviceByIdentifier(286);
```

## Scan and read tags

Once we have a reference to the NFC reader, we can use the `scan()` function to tell the reader to start scanning. When an NFC tag is placed on the reader, it will detect it and read the information that is stored on it:

```javascript
// We want to be informed when a new sensor value arrives
nfcReader.scan(readingDone, readingFailed);

function readingDone(val) {
    // Do something with the data from the NFC tag
}

function readingFailed(error) {
    // Handle reading errors
}
```

{% hint style="info" %}
The Tinkerforge Device Manager currently only support **NFC Forum Typ 2** tags. These include the NFC stickers and the NFC cards that are available on the [Tinkerforge shop](https://www.tinkerforge.com/de/shop/catalogsearch/result/?q=nfc).
{% endhint %}

When calling the `scan()` function, you must provide two callback functions as arguments: The first is called when the NFC reader has found and read a tag successfully, the second if the reader has found a tag, but there was an error reading it.

## Accessing the data

In the function `readingDone()` we have access to the data stored on the NFC tag via the parameter `val`. In the current version of the Tinkerforge Device Manager, the tag's information must be a simple JSON object with two fields. For example, this could be stored on a NFC sticker:

```javascript
{
    "id": 1,
    "type": 2
}
```

We can obtain this JSON object from the `val` parameter:

```javascript
function readingDone(val) {
    var id = val.id;
    var type = val.type;
    
    log("Read tag with ID " + id + " and type " + type;
}
```

{% hint style="info" %}
Writing data to an NFC tag is currently not supported by the Tinkerforge Device Manager. You can only work with the NFC tags and their current data stored on them.
{% endhint %}

## What to do when a tag was read?

When a tag was read, whether that was successful or not, the NFC reader goes into an idle status. To keep the reader in a state where it can detect and read tags, we can take the following measurements:

```javascript
// We want to be informed when a new sensor value arrives
nfcReader.scan(readingDone, readingFailed);

function readingDone(val) {
    // Do something with the data...
    
    // Set the reader back to scan mode
    nfcReader.scan(readingDone, readingFailed);
}

function readingFailed(error) {
    // Handle reading errors...
    
    // In case of an error, also go back to scanning mode
    nfcReader.scan(readingDone, readingFailed);
}
```

In the callback function `readingDone()`, we simply use `nfcReader.scan()` directly after we processed the data from the current tag. This puts the NFC reader back to scan mode. We must do the same in the `readingFailed()` function if we want to make sure the reader will always stay in scan mode.

{% hint style="info" %}
The `readingFailed()` callback is called when the NFC reader times out. This happens a few seconds after the `scan()` function was called and no tag was found. Therefore, in the above code example, it is quite normal that the `readingFailed()` function is called every so many seconds.
{% endhint %}

## Tweak: Wait a second before scanning again

In the example above, we put the NFC reader back to scan mode *directly* after we received the data from the current tag. As a consequence, we will see the same tag and its data many times because we can't remove the tag fast enough (and the reader is really fast). To prevent this issue, we can set a timeout of 1 second before we start scanning again:

```javascript
// We want to be informed when a new sensor value arrives
nfcReader.scan(readingDone, readingFailed);

function readingDone(val) {
    // Do something with the data...
    
    // Set the reader back to scan mode after 1000 ms
    setTimeout(setScanning, 1000);
}

function readingFailed(error) {
    // Handle reading errors...
    
    // In case of an error, also go back to scanning mode
    setTimeout(setScanning, 1000);
}

function setScanning() {
    nfcReader.scan(readingDone, readingFailed);
}
```


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