Electronic Systems: Sensors, Control, Outputs

Input, process, output

Every electronic system, from a burglar alarm to a games controller, follows the same simple pattern: an input senses the world, a control part decides what to do, and an output makes something happen. This module covers the three parts of an electronic system, the sensors, control devices and outputs you need to know, and the grade-9 habit of sorting components before you answer.

Input, control, output words

Five ideas run through electronic systems:

What does a sensor do?

In an electronic system, what is the job of an input sensor?

• It detects a change in the surroundings, such as light or temperature
• It produces a sound or light to alert the user
• It decides what the whole system should do
• It supplies power to the rest of the circuit

The systems model

Every electronic system has three stages: Input: a sensor detects a change, an LDR for light or a thermistor for heat. Control: a device processes the signal, such as a switch, transistor or resistor. Output: a device produces a result, such as a buzzer for sound or an LED for light. Trace any circuit as input, then control, then output.

Match each component to its job

Trace the signal

Put the stages of an automatic night light into the correct order.

• The LDR detects that it has gone dark
• It sends a signal to the control circuit
• The transistor switches the output on
• The LED lights up

Which are input sensors?

Select the TWO components that are input sensors.

• A light-dependent resistor
• A thermistor
• A buzzer
• An LED

Inputs versus outputs

Two kinds of device sit at opposite ends of a system.

Complete the system

Every electronic system has three stages. An _____ sensor detects a change; for example an _____ detects light and a _____ detects temperature. A control device such as a _____ then switches the circuit, and finally an _____ device such as a buzzer or LED produces the result.

What does a transistor do?

In the control part of a circuit, what does a transistor mainly do?

• It acts as an electronic switch, turning the output on or off
• It detects light and temperature changes
• It produces the sound in a buzzer
• It stores charge like a battery

Find the inputs

Here is a description of a greenhouse alarm's components. Tap the TWO that are input sensors.

• A thermistor measures the temperature.
• A transistor switches the circuit.
• An LDR checks the light level.
• A buzzer sounds the alarm.
• An LED shows the power is on.

Sort the system

An automatic security light switches on when someone approaches in the dark. Sort each component into the right part of the system.

• The circuit uses an LDR to check whether it is dark. Which part of the system is the LDR?
• A transistor switches the lamp on when the signal arrives. Which part is the transistor?
• An LED lamp then lights up. Which part of the system is the LED?

Design a system

A cold frame for plants needs an alarm that sounds if the temperature drops too low. Describe an electronic system for it, naming a suitable input, control and output device and what each does.

• Input: name a sensor and what it detects
• Control: name a device that processes the signal
• Output: name a device that produces the alert
• Explain how the signal flows from input to output

Sort the components first

Top answers sort the components first. Before you write, label each one as input, control or output: a sensor like an LDR or thermistor is an input; a transistor or resistor is control; a buzzer or LED is an output. Then describe the system in that order, input to control to output, and say what each part does. Sort first, then trace the signal - top band.