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System Diagrams

Introduction

System diagrams show how the different parts of a complex electronic system connect and interact. System diagrams are sometimes called block diagrams.

The boxes represent electronic sub-systems but do not give details of how the sub-system works. The arrows between the boxes represent the flow of information, not physical wires or other types of connection.

Basic System Diagram

basic system diagramThe most basic system diagram has an INPUT, a PROCESS and an OUTPUT ... and that's it. All systems can be expressed in terms of inputs, processes and outputs at the most basic level.


Minimal System Diagram

system diagramA more detailed system diagrams includes the names and functions of each sub-system and shows how they are connected together. However, details of the circuits used, component values and other technical data is not included in the system diagram.

The system diagram shown is for an outside light that comes on when movement is detected at night. The system diagram shows what sub-systems are required but not how they are implemented electronically.

The advantage of using a systems based approach to electronics is that each sub-system can be designed and tested separately which makes finding problems and mistakes much easier. In a large system different sub-systems can be designed and tested by different engineers as it is clear what each sub-system needs to do and how it relates to all the other sub-systems. Another advantage of a systems based approach is that one sub-system can be upgraded or modified as necessary without having to change the whole circuit.


Input Transducers

Input transducersInput Transducers convert information in the real physical world into electrical signals.

Input Transducers can produce either a digital or an analogue signal.

Many Input Transducers (LDRs, Thermistors, variable resistors) change their resistance as the environmental conditions change - these input transducers need to be used as part of a potential divider to convert the changing resistance into a changing voltage or current that can be processed.


Examples of Input Transducers include:

Processes

ProcessesProcesses respond to and process electrical signals from the input transducers. The processed electrical signals are then interpreted by the output transducers.

Examples of Processes include:
Combinational Logic operations (AND, OR, NOT etc)
Timers (monostables)
Oscillators producing pulses (astables)
Memory and Latches (bistables, flip flops)
Comparators (op-amp circuits)
Amplifiers
Counters (binary and decade)
Comparators (simple 1-bit ADC)
Micro-controllers


Transducer Drivers

Transducer DriversTransducer Drivers are necessary to increase the voltage, current (and consequently) power of the process sub-systems so that the output transducers can function correctly. For example, a logic gate can drive an LED sufficiently well but cannot drive a 24W bulb - in this case a transducer driver is required to increase the current available for the bulb.

Examples of Transducer Drivers include:
MOSFETs
Biploar Transistors
Electromagnetic relays
Power Amplifiers


Output Transducers

Output TransducersOutput Transducers convert electrical signals into effects in the real physical world. Output transducers can require high voltages or a large current to operate and so a transducer driver may be required to connect the process sub-system to the output transducer.

Output Transducers can be either digital or analogue.


Examples of Output Transducers include: