Download BoBT - Input Components - Sensors

SENSORS
INPUT COMPONENTS
Weblinks:
http://en.wikipedia.org/wiki/Sensor
http://en.wikipedia.org/wiki/Analog_device
INTRODUCTION
1. Light Dependent Resistor (LDR)
Sensors are devices which react to changes is environmental
conditions. There are two main types of sensor:
http://www.technologystudent.com/elec1/ldr1.htm
An LDR is a special type of resistor whose resistance varies
with the intensity of light shining on it. They are
used commercially in
 those whose resistance varies with a change in condition
 those who produce a voltage directly with a change in
condition
They are very different from switches in that they do not have
only high / low resistance but the size of their output depends
on the intensity of the change of the input condition, i.e. they
are analogue devices.
stimuli
night or day detectors in security lights
smoke detectors
In the dark they have a high resistance and as the light
intensity increases the resistance decreases.
Using LDRs
LDRs are always connected in a potential
divider with a variable resistor so that the
change in resistance is converted into a
voltage and the size of the voltage produced can be easily
changed. This is useful because the light level at which a circuit
switches can then be easily changed / set.
Dark
Light
DT@CGS: Electronic Products – EDEXCEL 2EP01
Vout = High
Vout = Low
Vout = Low
Vout = High
SENSORS
INPUT COMPONENTS
2. Thermistor
3. Moisture Sensor
http://www.technologystudent.com/elec1/therm1.htm
A thermistor is a special type of resistor whose resistance
varies with temperature. They are used commercially in
http://en.wikipedia.org/wiki/Soil_moisture_sensor
A moisture probe is a special type of resistor whose resistance
varies with moisture level. They are used commercially in
electronic thermometers
central heating systems
fire alarms
damp detectors
soil moisture
sensors in automatic
irrigation systems
humidity sensors
In the cold they have a high resistance and
as the temperature increases the resistance
decreases.
Using Thermistors
Thermistors are always connected in a potential
divider with a variable resistor so that the
change in resistance is converted into a voltage
and the size of the voltage produced can be
easily changed. This is useful because the
temperature at which a circuit switches can then be easily
changed / set.
Cold
Hot
Vout = High
Vout = Low
DT@CGS: Electronic Products – EDEXCEL 2EP01
Vout = Low
Vout = High
In the dry they have a high resistance and as the moisture level
increases the resistance decreases.
Using Moisture Probes
Moisture probes are always
connected in a potential divider with
a variable resistor so that the
change in resistance is converted
into a voltage and the size of the voltage produced can be easily
changed. This is useful because the moisture level at which a
circuit switches can then be easily changed / set.
Dry
Wet
Vout = High
Vout = Low
Vout = Low
Vout = High
SENSORS
INPUT COMPONENTS
4. Piezo Sensor
5. Biosensor
http://en.wikipedia.org/wiki/Piezoelectric_sensor
A piezo sensor is a special type of senor that
uses the piezo-electric effect to produce a
voltage in response to pressure. They are used
commercially in
http://en.wikipedia.org/wiki/Biosensor
A biosensor is a special type of senor that
produces a voltage when pressed. They are used
commercially in
guitar pick-ups
electronic drum kits
tactile sensors in robotic arms
The higher the pressure the higher the voltage
produced.
Using Piezo Sensors
Piezo sensors are always connected in a potential divider with a
variable resistor so that the size of the
voltage produced can be easily changed.
This is useful because the pressure at
which a circuit switches can then be
easily changed set.
Pressure
Vout = High
No Pressure Vout = Low
DT@CGS: Electronic Products – EDEXCEL 2EP01
Vout = Low
Vout = High
blood sugar level monitors
air and water quality
monitors
food pathogen detectors
Other Types of Sensor
The sensors below are not on your Specification but they may
be useful in your controlled assessment:
Microphone
http://en.wikipedia.org/wiki/Microphone
Microphones convert sound into a voltage.
Quantum Tunnelling Composite Tunnelling (QTC)
http://en.wikipedia.org/wiki/Quantum_tunnelling_composite
QTC is a flexible polymer which in its normal
state is an insulator. However when it is pressed
it becomes more or less a perfect conductor.
http://www.youtube.com/watch?v=3_9duPm-rzc
It is used commercially in
weighing scales
eTextiles
tactile sensors in robotic hands