Www Electronicdesign Com Sites Electronicdesign com Files Ifd2668 Fig1
Www Electronicdesign Com Sites Electronicdesign com Files Ifd2668 Fig1
Www Electronicdesign Com Sites Electronicdesign com Files Ifd2668 Fig1
Www Electronicdesign Com Sites Electronicdesign com Files Ifd2668 Fig1
Www Electronicdesign Com Sites Electronicdesign com Files Ifd2668 Fig1

Combine Modified CD Optical Assembly, PSoC for High-Resolution Microgram Measurements (.PDF Download)

March 23, 2018
Combine Modified CD Optical Assembly, PSoC for High-Resolution Microgram Measurements (.PDF Download)

The ability to measure microgram and milligram masses with extremely high accuracy is often critical in pharmaceutical and chemical industries. This design combines a pickup head from a compact-disc (CD) system and a millimeter-sized cantilever mounted on the CD’s optical pickup head (OPH) to build an alternative, cost-effective microbalance. This simple setup interfaces to a personal computer through a PSoC microcontroller for read out (Fig. 1).

1. The microbalance setup uses a standard CD’s optical pick-up head with an attached millimeter-size cantilever supported with a PSoC embedded design.

Since the CD OPH is designed to measure the variation in the reflecting surface of CD, this design offers resolution of better than 2 μm for the displacement of the added cantilever, which is 25 mm long, 6 mm wide, and 0.43 mm thick (Fig. 2). It offers microgram-scale accuracy at lower cost and with greater sensitivity than microbalances based on the piezoelectric effect.

2. Shown is the CD’s optical pick-up head mounted with millimeter-size cantilever (this is the key element of this mass sensor arrangement) connected with an embedded PSoC design functioning as a microbalance.

In normal CD-player operation, the unit’s OPH laser diode (780 nm) uses a linearly polarizing beam splitter, collimator, objective lens, and anamorphic lens placed in front of the detector array, plus a focusing voice coil and its drive motor. The laser beam is directed to the specimen via the objective lens, which is actuated by the voice-coil motors. The CD surface, in turn, scatters the beam back through the objective lens to the beam splitter, where it’s directed via the anamorphic lens onto the four-quadrant photodiode (QPD).

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