Inputs are things that are put in to the system. They can be activated mechanically (e.g. a switch), or sense a change (e.g.
sensor).
Systems:
•Electronic systems are broken down into stages.
•The main stages are the inputs, processes and outputs.
•Systems diagrams tend to be drawn as flow charts.
Light Sensors:
•Component name: Light dependent resistor (LDR).
•A light sensor that is sensitive to a change in light.
•Its resistance increases in the dark so can act as a switch turning on
street lights in the dark and off in the light.
Temperature Sensor:
•Component name: Thermistor.
•A temperature sensor that is sensitive to a change in temperature.
•Its resistance increases with a change in temperature so can act as a
switch turning the oven on when it is too cold and off when it has
reached the desired temperature.
Switches:
•Mechanical switches are added to systems, allowing them to be
turned on and off.
Pressure Switch:
•Component name: Pressure switch.
•A pressure switch is sensitive to a pressure or weight being applied.
•It can be used in cars to remind the driver to fasten their seat belt.
Toggle Switch:
•Component name: Toggle switch.
•Once switched on a toggle switch will complete the circuit and it will
remain on until it is turned off and the circuit is broken.
•It is used for light switches.
Push to Make Switch:
•Component name: Push to make (PTM) switch.
•This circuit is usually off and when you push the switch the circuit is
completed and turned on.
•A good example of this is the door bell, whereby it rings when pushed.
Push to break (PTB) Switch:
•Component name: Push to break (PTB) switch.
•This circuit is usually on and when you push the switch the circuit is
broken and turned off.
•This can be used in a lift when the user wants the door to be kept
open for longer by pressing a button.
Unit 2
