2010 · 99 citations · 0 references
EngineeringElectrical EngineeringMechatronics EngineeringAnalog ElectronicsInstrumentationMovement AnalysisGait AnalysisGait AssessmentMotion CaptureMotion SensorsPhysical Activity AssessmentWalking PerformanceAcceleration SensingGait Analysis InstrumentationMotion Capture SystemsMotion SensingPhysical Activity MonitoringSensor-based Gait MonitoringStep CountingWalking Speed
Acceleration is the key parameter for analyzing walking and running, with motion decomposed into forward (roll), vertical (yaw), and side (pitch) components along three axes. The study presents a reference design of a full‑featured pedometer using the ADXL345 accelerometer to recognize and count steps while measuring distance, speed, and calories. The design employs the ADXL345 3‑axis accelerometer, which senses acceleration along x, y, and z axes and operates effectively regardless of device orientation. The ADXL345’s 32‑level FIFO buffer reduces host processor intervention and saves power, while its 13‑bit resolution permits accurate measurement of low‑speed walking steps.
This article, based on a study of the characteristics of each step a person takes, describes a reference design using the 3-axis ADXL345 accelerometer in a full-featured pedometer that can recognize and count steps, as well as measure distance, speed, and—to an extent—calories burned. The ADXL345’s proprietary (patent pending), on-chip, 32-level first-in, first-out (FIFO) buffer can store data and operate on it for pedometer applications to minimize host processor intervention, thus saving system power—a big concern for portable devices. Its 13-bit resolution (4 mg/LSB) allows pedometers to even measure low-speed walking (where each step represents about 55 mg of acceleration change) with reasonable accuracy. Understanding the Model From the characteristics that can be used to analyze running or walking, we choose acceleration as the relevant parameter. The three components of motion for an individual (and their related axes) are forward (roll), vertical ( yaw), and side (pitch), as shown in Figure 1. The ADXL345 senses acceleration along its three axes: x, y, and z. The pedometer will be in an unknown orientation,