A method and apparatus for performing modulated fluid delivery and aspiration during a surgical procedure such as phacoemulsification is provided. In certain configurations, a magnetic structure includes one or more pairs of magnets positioned within a housing. As an example, the rigid object can be a leg bone where the proximal end is at the hip joint and the distal end is at the knee. A first output latch is configured to receive an output of the first multiplexer to provide a select signal for the second multiplexer and to drive the dynamic feedback signal to an even half summer circuit of the summer circuits.