Technician Handbook ! 673 Electronic & Computer Controlled Systems Simple ECU Inputs Signals from switches and sensors can supply information to the ECU in several ways. Voltage ON/OFF – A simple switch opens or closes a circuit. It is the presence or absence of voltage in the circuit that signals the ECU. Variable Voltage – Some sensors produce a voltage that changes depending on the conditions the sensor is measuring. The amount of voltage produced at any given moment provides information about the condition at that time. Variable Resistance – In other types of sensors, electrical resistance increases or decreases as external conditions change.
Sensing the changing voltage as a result of changing resistance in the circuit signals the ECU what the conditions are. Variable Pulse Pattern – Another method for signaling the ECU about changing conditions is to turn a circuit on and off rapidly at a particular frequency. This works especially well for signaling rotational speed. It is the frequency of the ON/OFF pulses that supplies information to the ECU. 8 Technical Training