In this page, we show the analogue circuit schematics of the feedback control for the second-stage magnetic suspension experiment.
The schematics is shown in the figure below:
This circuit has four paths. The first and the last paths control one tilt and one vertical motion. The middle two paths are balanced differential control of the other tilt degree of freedom. Within each path, there are four main parts: (i) Subtraction, from which we obtain the error signal from the photodiode; (ii) Differentiation to compensate the phase and obtain desire phase margin from 5 Hz to 20 Hz; (iii) Integration to achieve integration from 0 Hz to 1 Hz. (iv) Gain tuning to tune the gain of the feedback loop.
In addition, we use Rana's Sallen key low-pass filter to drive the LEDs.
The corresponding board is shown in the following figure:
