Input - Sensors

Switches allow the circuit to be open or closed. When a button/switch is pushed, the circuit becomes closed and becomes active. When the switch is in the off position, the circuit is open and therefore is not active.

Light switch: Moving the toggle moves the switch to the on or off position.

Rotary switch on an oven: turning the knob makes different connections for the different functions.

The keypad: these switches only stay on while the button is held down.

Push buttons on a washing machine. These only stay switched on while the button is held down.

These pushbutton switches are called momentary contact as they release once you remove your finger.

Motion sensors detect movement which sends a signal to the processor which activates an output.

Speed camera: when a speed is detected that is above the speed limit it takes a photo. L

Outdoor motion sensor: When movement is detected it turns a light on for a set period. Usually this type of detector also has a light sensor so it only works at night.

Sensor tap: When the sensor detects your hands under the spout it activates an electronic valve that lets the water flow.

Automatic hand dryers: Like the tap, they only operate when they detect your hands.

A light sensor detects low levels of light and sends a signal to the processor which activates the output.

The camera has a very sensitive light sensor that can record an image electronically.

Street lights have a sensor so they only turn on when it is dark.

Sound sensors work by turning sound into an electrical signal. They are generally analogue signals and need to be converted to digital.

Microphone turns sound into an electric signal allowing it to be recorded or sent to someone else.

Guitar tuner: The guitar tuner works by detecting the frequency of the sound and comparing it to the correct frequency for each string. It then indicates which way you need to adjust the tune to make it correct.

Voice activated controls: These systems can recognise words in order to provide instructions to the microprocessor. Siri is an example of this.

Level sensors work by detecting the level of a liquid and sending a signal which could be either digital or analogue back to the controller. This is usually done with a float that moves up and down in the tank.

The fuel level sensor sits inside the fuel tank. A float on an arm moves a potentiometer in order to vary the voltage input to the controller.

A bilge pump switch uses a float to detect water in the bottom of a boat and can turn on an alarm or a pump.

Other level sensors are used in water tanks and brake fluid reservoirs in cars.

Pressure sensors work by sending a signal to a processor when pressure is applied e.g. on a keypad for a house alarm. Once the signal is processed, an output occurs e.g. deactivates the house alarm

The keypad detects pressure on each button to provide a signal to the microcontroller.

Some shoes have sensors inside them to detect pressure when walking. This signal to the microprocessor makes LEDs light up.

Scales are used to measure the weight of things. It does this by detecting the pressure applied to the top.

Other pressure sensors include oil pressure sensors in an engine.

Thermal sensors work by sensing a predetermined temperature which signals the processor which activates an output e.g. light turns on or off.

Air conditioning controllers are easily adjusted by the user and provide an input to the controller when the temperature is too high or too low.

Oven thermostats are similar. You can see when the temperature is low as ovens usually have a light to indicate when the element is heating the oven.

Mechanical sensors rely on something moving to trigger them. The motion could be from a person in the case of the volume control or from the speed of a wheel.

Volume control knobs can be turned by hand to adjust the volume. They have a potentiometer behind the knob that varies the input to the system so it can adjust the sound as required.

Temperature selector on an iron. This adjusts the iron controller to turn the heating element on or off to adjust the temperature. (Some irons have a mechanical temperature control and are not electronically controlled).

Micro switches are used to detect movement in mechanical systems and tell the processor when this happens so it can control other parts of the system. This switch was on a lift and stops the motors when the door is fully opened.