System-Block Diagrams


  • These are quite like flowcharts in that they are also blocks interconnected by arrows to show the functions of a product, circuit, or part of a circuit.
  • The difference is that such diagrams are normally quite simple, and consist entirely of rectangular blocks.
  • However, both system block diagrams and flow charts can be closed looped or open looped.
  • Also known as systems diagram.


  • Such diagrams are a simple progression from input, to process, to output.
    • Input – A sensor or switch which triggers a process.
      • It is something that takes in energy of some form and transforms it into an electrical signal.
      • This is a signal from input transducers.
      • The power supply is never part of the systems diagram.
    • Process – The decision of what action to take.
      • This is, in electronics, decided by the process component or components.
    • Output – The action that results from the input.
      • This is produced by output transducers.

Open Looped Diagram

  • The above is an example of a open-looped system-block diagram.
  • Such a system does not allow for any control because no feedback is available.


  • Such diagrams are just like open-looped diagrams but include a feedback as well as inputs, processes and outputs.
    • Feedback – This is generally a question just like the YES/NO questions found in decision blocks in flowcharts, which determines whether or not more action must be taken and, if so, should this action be just a repetition of what had previously been done.
      • It is a response usually provided by the user of a product.
    • Storage (optional) – This is only possible when there is information or material to be stored and may happen when the action that is dictated by the process component requires a certain amount of information or material to be gathered before any output is decided upon.


  • The above are examples of closed-loop system block diagrams.


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