Page 74 - Handbook of Biomechatronics

Sensors and Transducers 69

Fig. 9 (A) Example of a potentiometer. (B) Circuit diagram with a potentiometer. As the
potentiometer is adjusted, the resistance changes, varying the intensity of the light bulb
in the circuit.

There are several types of potentiometers (Newark, n.d.). There are sin-
gle turn, partial turn, and multiturn potentiometers. There are also linear and
logarithmic, referring to the rate of change of the resistance. They come in a
multitude of sizes and shapes, from very large for heavy machinery sensing,
to tiny integrated circuit chips for setting microprocessor inputs. They are
useful for sensing device position or for setting controls on a device.
You select a potentiometer for Jacob’s motor-driven knee which allows
him to adjust how freely the knee moves. When Jacob turns the potentiom-
eter, the resistance changes which varies the voltage signal sent to the micro-
processor. The microprocessor uses that signal to adjust system values which
effects the function of the knee.

3.3 Photoresistor
A photoresistor or light-dependent resistor (Fig. 10) is composed of photo-
conductor material. When light hits this material, the material absorbs the
radiation and electrons move from the valance band of the semiconductor
to the conduction band. The more electrons in the conduction band of the
resistor, the less the resistance of the resistor (http://www.resistorguide.
com/photoresistor/, Accessed 22 August 2017).
InJacob’sprostheticfoot,youinstallaphotoresistorontheside.Whenthis
resistor islightactivated, thesystemassumesthatJacobisnotwearingashoe in
his foot. When the resistor is not light activated, the system assumes Jacob is
wearing a shoe. Minor variations in prosthetic system performance are intro-
duced into the system control algorithm based on the light sensor input.