Optimal Varioptic Lens Focus for Biophysical Microscopy (2013)

Undergraduate: Patrick Heenan

Faculty Advisor: Russell Taylor
Department: Physics & Astronomy

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Panoptes is a 12-way parallel microscope used by the Center for Integrated Microscopy and Manipulation (CISMM) at Chapel Hill. Currently, the drivers of the lenses, which operate at high voltage, interfere with each other. The voltages driving adjacent channels contribute significantly to their neighbor¿s voltage amplitudes. It is desired that these lenses be independent for optimum imaging. In order to prevent crosstalk between the drivers of the lenses, this project will improve the shielding of the drivers to decrease parasitic capacitance, phase lock the modulation frequencies of the drivers, and implement a PI feedback loop to maintain the desired control voltage and hence focus. Using microcontrollers with pulse width modulators, interrupts and analog-to-digital converters, the desired root mean squred (RMS) voltage in the range 0-60 Volts was maintained within an error of 30 milliVolts RMS. The overhead of a single iteration of the PI loop is approximately 41 microseconds, with a settling time of approximately 10 iterations.