Introduction

The transducer is a device that converts one form of energy to another. For interfacing to a microcomputer, we are primarily interested in the electronic transducer, which has an input or an output that is electrical in nature, such as a voltage, current, or resistance. The sensor is an electronic transducer that converts a physical quantity into an electrical signal. An actuator is an electronic transducer that converts electrical energy into a physical quantity, and is an essential element in control systems.

Sensors are used to detect displacement, temperature, strain, force, light, etc. Almost all sensors require additional circuits to produce the voltage and current needed for analog-to-digital conversion. As we shall see in this chapter, the thermistor changes its electrical resistance as a function of temperature, and a bridge is needed to produce a corresponding voltage, whereas the silicon photodiode produces a current, and a stage of amplification is needed to produce a voltage. Often, the term “sensor” includes both the transducer and the circuits needed to produce an output voltage.

Laboratory Exercise 11 uses a circular resistor and a computer to record angle and the oscillations of a damped pendulum. Laboratory Exercise 12 explores the measurement of temperature using the dial thermometer, a platinum resistance thermometer, the thermocouple, and the thermistor. Laboratory Exercise 13 measures force, using four metal foil strain gauges bonded to a plastic rod and wired in opposing pairs to form a bridge circuit.