A Low-Cost, DC/Low-Frequency Response FM/FM Telemetry System for Orthopedic Gait Analysis, Biomechanical Measurements, and Other Applications

Abstract

This paper is intended to describe the design, operating principles, and implementation of a telemetry instrumentation system. The essential characteristics of the system are: 1) It is effective for the acquisition of data in the dc to 40 Hz frequency range. 2) The remote unit is lightweight and small (on the order of ounces and a few cubic inches). The exact dimensions and weight are variable according to purpose. 3) The transmission radius is nominally fifty feet. 4) The output voltage (the analog) is a linear function of input voltage, to approximately ± 0.5% over the operating range. 5) The system can be used with any transducer producing a voltage output. Two examples discussed will be potentiometers and a four-state (four voltage level) "logic" circuit. These are used in the orthopedic experiment, which will be discussed briefly. Another example is the Wheatstone bridge strain gauge transducer, used to measure force, in an entirely different experiment. 6) Several complete systems may be operated simultaneously to form one multi-channel system. This is the case for the orthopedic experiment, which will serve as a backdrop in explaining the system function. 7) The system is constructed from available discrete components, integrated circuit functional blocks, and assembled commercial products. The cost is on the order of 10% of similar performance characteristic commercial telemetry.