QR Codes with the Barcode module
It looks like a barcode is just a piece of encoded text from the .module file:

/**
 * Implements hook_field_info().
 */
function barcode_field_info() {
  return array(
    'barcode_field' =&gt; array(
      'label' =&gt; t('Barcode'),
      'description' =&gt; t('This field stores a barcode in the database.'),
      'default_widget' =&gt; 'barcode_textfield',
      'enable_tokens' =&gt; 1,
      'default_formatter' =&gt; 'barcode_default',
    ),
  );
}


So what you likely want to do is creating link fields that upon form submission pass their values onto the barcode field(s) as well. Then, you will show the barcode field(s) on any pages you want and hide the raw link field from the users view (unless their editing the entry).

You could look at the Rules module to automate this for you if you don't want to write a module (for example, when a new piece of content of type Foo, if field link is blah, copy field value to field my_barcode value). Look into the Form API to hide (with #access)the field_barcode values in the edit form (as they are dynamic end-user stuff).

The only thing that the Link field gives you over putting the raw url link in the bar_code field itself is extra form validation for free (for example, check it is a valid URL).