Inputs provide the computer with system operation information or driver requests. Driver input signals are usually provided by momentarily applying a ground through a switch. Switches can be used as an input for any operation that only requires a yes-no, or on-off, condition. Sensors convert some measurement of vehicle operation into an electrical signal. There
FIGURE. Principle of feedback signals. If the computer sends a command signal to open a blend door in an automatic climate control system, a feedback signal may be sent back from the actuator to inform the computer the task was performed. The feedback signal will confirm both the door position and actuator operation (Figure 10-32).
Switches are simplest of all input devices. The computer monitors the two states of the switch by measuring the voltage on the sense circuit. There are two types of voltage sensing circuits used with switches; the pull-down circuit and the pull-up circuit. Basically, the pull-down circuit will close the switch to ground and the pull-up
Many electronic systems require input data concerning position, motion, and speed. Most motion and speed sensors use a magnet as the sensing element or sensed target to detect rotational or linear speed. The types of magnetic speed sensors include magnetoresistive (MR), inductive, variable reluctance (VR), and Hall-effect. In addition, the potentiometer and commutator pulse counting
This section discusses the various types of pressure sensors that are used in automotive applications. In some instances, a simple pressure switch is used. In systems that require monitoring of the exact pressure electromechanical pressure sensors, piezoresistive, or piezoelectric sensor are used. These sensors convert the applied pressure to an electrical signal. A wide variety
Thermistors are commonly used to measure the temperature of liquids and ambient air. A thermistor is a solid-state variable resistor made from a semiconductor material, such as metal oxides, that have very reproducible resistance verses temperature properties. FIGURE. A thermistor is used to measure temperature. The sensing unit measures the resistance change and translates the
FIGURE. The input signals are processed in the microprocessor. The microprocessor directs the output drivers to activate actuators as instructed by the program. The microprocessor receives inputs that it checks with programmed values. Several types of input devices are used to gather information for the computer to use in determining the desired output. Many input