public function fetchQRCodeUrl($refUrl) {
        $size = 150;
        $EC_level = 'L';
        $margin = 0;
        $trail = '?qr=1';

        return self::CHART_API_URL
                .'chs='.$size.'x'.$size.'&cht=qr'
                .'&chld='.$EC_level.'|'.$margin
                .'&chl='
                .urlencode($refUrl.$trail);
    }