private function _voltage()
    {
        $volt = null;
        if (CommonFunctions::rfts('/sys/devices/platform/sunxi-i2c.0/i2c-0/0-0034/axp20-supplyer.28/power_supply/ac/voltage_now', $volt, 1, 4096, false) && !is_null($volt) && (($volt = trim($volt)) != "")) { // Banana Pi
            $dev = new SensorDevice();