Light sensors measure the amount of light (visible, infra-red or laser light). These sensors have a variety of different applications, including:
- CCD (cameras)
- Barcode Readers
- Optical Drives
- Detecting changes in passive infra-red light levels (see motion sensors)
Passive Infrared Sensors
These sensors detect motion by measuring changes in the the amount of infrared radiation being emitted by an object. Mammals give off heat and so these sensors can be used to detect mammals and so can be used in security systems or wildlife tracking systems.
Used to detect the PH levels in liquids and in the soil. Especially important in controlled agricultural environments where adverse PH levels can cause crops to fail.
Carbon Monoxide Sensors
Used in environments where methane gas levels need to be detected. Methane gas is the gas used in natural gas powered homes (the gas that sometimes powers gas hobs). It is highly explosive and so needs to be controlled, especially in mines where methane gas levels can easily build up to fatal levels.
There are different types of magnetic sensors.
- Some use coils to detect changes in the magnetic flux density
- Some use reed switches that close the circuit when a magnetic is placed nearby.
- Some use hall elements to detect magnetism.
- Others use different techniques.
Vibration Sensor (Microphone)
Ultrasonic Sensors (Short distances <2m)
Ultrasonic distance sensors use pulses of ultrasonic sound to detect the distances of objects.
This is a similar to the technique that bats use to navigate in darkness.
Laser Range Finders (Long Distances <5km)
Laser range finders fire a pulse of laser light at an object and measure the time that it takes for the light to bounce off the object and return to the sensor. This time is used to measure the distance to the object.