Systems Approach to Designing


Like energy generation and computer aided design, electronic systems also have an input – process – output with the electrical signal passing through the three (a circuit). You should be able to consider electrical systems when you are designing and be confident in your products functionality.

Inputs are the signal which makes the system work.


  • Light sensor: LDR’s could turn a light on when it gets dark or off when it gets light. Used in security lighting.

  • Moisture sensors: activated with water droplets.

  • Peizoelectric sensors: Change when they are deformed with heat, force, temperature etc.

  • Temperature sensor: Thermistor switches something on or off depending on the temperature. Used in central heating, car radiators.

  • Switches: Pushing a button, sliding a switch or flicking a switch all complete the circuit to turn things on. Light switches, torches, toys.

  • Push to make (PTM): A switch which allows the flow of electricity only when it is held in. Used in keyboards, doorbells.

  • Microswitch: A small lever switch.

  • Reed switch: A switch controlled by magnetic fields.

Systems Approach to Designing, figure 1


Put simply processes take the input and change it into the output.

Integrated Circuits (IC’s): Tiny circuits which can include millions of components. They are a cheap, small and low energy. Used in small electricals, mobile phones, games controllers etc.

Resistors are colour coded components that work with in puts and processes to regulate the flow of electricity. They can protect things like bulbs from blowing if a pulse of electricity goes through it. A variable resistor can alter continually as its works, used in things like volume controls.

Microcontrollers are tiny computer chips they can take several inputs and change them into several output decisions. A microcontroller is different from an IC in that it can be reprogrammed using programming language. Found in nearly every electrical appliance. They can be used as timers – counting electrical pulses, such as car indicators and used as counters counting revolutions such as drill speeds or bicycle speedometers. Microcontrollers can also collect information to make decisions (called logic gates) such as a washing machine would have to have the door shut and the setting selected before the cycle starts. Logic gates are logically named – OR gates have 2 inputs, either/or. AND gates have 2 inputs and they need both to switch on. NOT gates have 1 input and if it’s on, the output is off.

Relay: An electromagnetic device to send a signal from one circuit to open or close another.

Bipolar transistor: Used to amplify voltage or power.


Systems Approach to Designing, figure 1

The output is what your electrical product has to do.

  • Responding to the input signal makes the output happen.

  • Common ones to appear in your course work and exams are LED’s, lights, buzzers, loudspeaker, motors – there are millions!

Flowcharts are used to plan programming in microchips. All flow charts start and end with an oval shaped terminator. Inputs and outputs are shown as parallelograms, processes are square boxes and decisions are in diamonds with a yes and no arrow (logic gates).Sequence arrows join the boxes in the order, flow charts can be simple or highly complex.

Environmental controls:

The Restriction of Hazardous Substances RoHS directive is used to control the use of hazardous substances in electrical equipment such as lead, mercury and cadmium. This monitors the amount of materials in separate components when put together to create a product to check they remain at safe levels.

The Waste Electrical and Electronic Equipment (WEEE) directive has come into force to try and ensure the safe disposal of obsolete electrical equipment with as little environmental impact as possible.