I have a php file that has all my database credentials using PDO.

I have a class file that contains all my classes. In the class file I find myself creating the database connection in every function:

class myClass {
    /* Properties */
    private $conn;

    /* Get database access */
    public function __construct(\PDO $pdo) {
        $this->conn = $pdo;
    }

}

What should I be doing so that I am not doing this in every class?