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Complex electronic systems can be broken down into simpler sub-systems. This makes it easier to understand, design and test the circuits.
Systems typically have ...
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INPUT/S - Sensing
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Light,
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Temperature
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Magnetic field
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Pressure
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Moisture
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Sound
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Movement or Rotation
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PROCESS/ES
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Comparator
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Logic gates
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Latch
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Time delay
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A to D Converter
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D to A Converter
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Microcontroller
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OUTPUT/S
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Lamp or LED
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Warning buzzer
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Solenoid
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Actuator, Motor or Servo
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Loudspeaker
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Most output transducers need a DRIVER.
Sub-systems and System Diagrams (Labelled boxes joined with arrows)
System diagrams are used to describe systems and sub-systems.
Dividing a system into sub-systems is a good idea because a whole system can be hard to understand.
Each sub-system can be quite simple.
Complex systems are only possible because different teams of designers and testers are responsible for each sub-system.
Many sub-systems can be purchased pre-built and tested.
Example: Turn on a lamp when it gets dark.
To achieve this you'd need ...
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A light sensor in a voltage divider circuit.
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A comparator to sense when the light sensor detects it's too dark
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A driver because the comparator is not able to drive the relay without some help.
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An electromagnetic relay because this can switch high voltage AC mains.
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A lamp


Circuit Diagram (Don't confuse circuit and system diagrams)

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It's possible to design and test each sub-system on its own.
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Frequently needed sub-systems like the relay are mass produced at low cost.
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The same sub-systems can often be used to solve many different problems.
A More Complex Example
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Decoupling Capacitor
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Voltage Divider - a fixed reference voltage
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Voltage Divider - a light dependent voltage that decreases as it gets dark
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Op Amp Comparator. In daylight, the output is LOW. At night, the output is HIGH.
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555 Astable. At night, the reset pin is HIGH and the astable oscillates causing the lamp to flash. In daylight, reset is LOW and the lamp is OFF.
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Transistor Switch Transducer Driver. The transducer is the lamp.

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