yea, it need to be numeric: 

```
// Iterate over the JSON properties.
  foreach ($data as $key => $value) {

    // If the key is "timestamp", skip to the next property in the JSON.
    if ($key == 'timestamp') {
      continue;
    }

    // If the value is not numeric, skip it.
    if (!is_numeric($value)) {
      continue;
    }

    // Process notifications.
    farm_sensor_listener_process_notifications($sensor, $key, $value);

    // Create a row to store in the database;
    $row = array(
      'id' => $sensor->id,
      'timestamp' => $timestamp,
      'name' => $key,
    );

    // Convert the value to a fraction.
    $fraction = fraction_from_decimal($value);
    $row['value_numerator'] = $fraction->getNumerator();
    $row['value_denominator'] = $fraction->getDenominator();

    // Enter the reading into the {farm_sensor_data} table.
    drupal_write_record('farm_sensor_data', $row);

    // Invoke hook_farm_sensor_listener_data().
    module_invoke_all('farm_sensor_listener_data', $sensor, $key, $value);
  }
```