Page 35

EDNE MAY 2015

designideas De-embed transmission lines with FIR filters Rotational (or linear) measurement using an optical mouse sensor By Anatoly Besplemennov  This Design Idea utilises an optical computer mouse’s sensor for measuring rotation of a disc which can be mechanically connected to any sort of rotating apparatus. One feature is to allow adjustment of the pulses per revolution by changing the sensor’s position along the disk radius. The CMOS optical sensor of the mouse chip provides a non-mechanical tracking engine. Inside the chip, images are captured, digitised, and digitally processed. For instance, let’s consider the simple and low cost OM02. The sensor measures position by acquiring surface image frames and mathematically determining the movement direction and value. The sensor is mounted in a polystyrene optical package and is designed to be used with a high intensity LED. It provides a complete and compact tracking engine. It has no moving parts and requires no precise optical alignment. The OM02 produces a quadrature output for both X and Y directions of movement. The resolution is about 0.0025 inches (0.064mm), and the motion speed, up to 16 inches per second (40 cm/sec). The IC generates a quadrature X-direction output signal which emulates an ordinary encoder’s output. Both X & Y can be used for a 2D system. X1 and X2 quadrature signals are generated at a maximum frequency of about 25 kHz. The following diagrams show the timing for positive X motion (to the right direction). The quadrature output can be used for direct stepper motor control if needed. According the IC datasheet, we can use the internal oscillator, in which case Cosc may not be needed. Rosc defines the frame rate: lower values correspond to higher rates. Connecting the X1 34 EDN Europe | MAY 2015 www.edn-europe.com


EDNE MAY 2015
To see the actual publication please follow the link above