MPXM2102AS datasheet(125/670 Pages) MOTOROLA

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Motorola Sensor Device Data

www.motorola.com/semiconductors

AN1635

Baseball Pitch Speedometer

Prepared by: Carlos Miranda, Systems and Applications Engineer and

David Heeley, Systems and Applications Mechanical Engineer

INTRODUCTION

The Baseball Pitch Speedometer, in its simplest form, con-

sists of a target with acceleration sensors mounted on it, an

MCU to process the sensors’ outputs and calculate the ball

speed, and a display to show the result. The actual imple-

mentation, shown in Figure 1, resembles a miniature pitching

cage, that can be used for training and/or entertainment. The

cage is approximately 6 ft. tall by 3 ft. wide by 6 ft. deep. The

upper portion is wrapped in a nylon net to retain the baseballs

as they rebound off the target. A natural rubber mat, backed

by a shock resistant acrylic plate, serve as the target. Accel-

erometers, used to sense the ball impact, and buffers, used to

drive the signal down the transmission line, are mounted on

the back side of the target. The remainder of the electronics

is contained in a display box on the top front side of the cage.

Accelerometers are sensors that measure the accelera-

tion exerted on an object. They convert a physical quantity

into an electrical output signal. Because acceleration is a

vector quantity, defined by both magnitude and direction, an

accelerometer’s output signal typically has an offset voltage

and can swing positive and negative relative to the offset,

to account for both positive and negative acceleration. An

example acceleration profile is shown in Figure 2. Because

acceleration is defined as the rate of change of velocity with

respect to time, the integration of acceleration as a function

of time will yield a net change in velocity. By digitizing and

numerically integrating the output signal of an accelerometer

through the use of a microcontroller, the “area under the

curve” could be computed. The result corresponds to the net

change in velocity of the object under observation. This is the

basic principle behind the Baseball Pitch Speedometer.

Figure 1. David Heeley, mechanical designer of the Baseball Pitch Speedometer Demo,

tests his skills at Sensors Expo Boston ’97.

MOTOROLA

SEMICONDUCTOR APPLICATION NOTE

REV 1

Freescale Semiconductor, Inc.

For More Information On This Product,

Go to: www.freescale.com

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