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High Sensitive Light Sensor
A simple understanding of a simple sensor
When you use your digital camera to take photo in automatic mode then
how does camera detect that either flash is required or not? Same thing
you can remark with automatic solar street light which turns on in
night and gets turned off on morning.
These equipments are made possible just by using light sensor. This
project will give you an idea to make and to understand the high
sensitive light sensor.
Concept:
Concept: To make this project possible we need one device which can
change its property by changing the light intensity spread over it. Light
dependent resistor (LDR) is one such device. Light Dependent Resistors
are very useful especially in light/dark sensor circuits. Normally the
resistance of an LDR is very high, sometimes as high as 1000 000 ohms,
but when they are illuminated with light resistance drops dramatically.
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Circuit Diagram
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What is comparator?
A comparator is a device which compares two voltages or currents
and switches its output to indicate which is larger.
How does OpOp-amp act as comparator?
An operational amplifier (op-amp) is a device with two inputs and a
single output. The output of the amplifier VO is given by the formula
when there is no feedback:
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VO = A (V+ -- V-)
Where A is the open-loop voltage gain of the amplifier, V+ is the noninverting input voltage and V- is the inverting input voltage. Both V+
and V- are node voltages with respect to ground. Typically, the openloop voltage gain A is on the order of 105 to 106. Since the gain, A, of an
op-amp is very large; any difference will be magnified to the power
supply rails ±Vcc.
Vcc. If V+is greater than V- then the difference V+ -- V- will
be positive and the result will be amplified to Vcc.
Vcc If, however, V- is
greater, then the difference is negative and the result will be amplified
to –Vcc
Vcc . Finally, if the two voltages are exactly equal, then the
difference will be zero and the output will also be zero. So, it completes
the requirement of comparator.
Circuit Description:
This project has been tested in lab. An integrated circuit "Voltage
Comparator" is equivalent to an Operational Amplifier, Such as the
LM358 or LM324. For detail about LM358 please see its datasheet.
For these circuits the reference voltage is fixed at one-half of the supply
voltage while the input voltage is variable from zero to the supply
voltage. In theory the reference and input voltages can be anywhere
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between zero and the supply voltage but there are practical limitations
on the actual range depending on the particular device used.
In the given circuit diagram Pin3 and Pin2 are non-inverting and
inverting terminals respectively. Voltage at Pin3 (say V+) is kept
constant by means of variable resistor R3. R3 can be used to increase
and to decrease the sensitivity of the LDR towards the light intensity
incident on it. With the help of resistors R1 and R2, voltage at Pin2 (say
V-) is made constant so that when there is no light (at low intensity
light) the LDR acts as open circuit and the output voltage Vo at Pin1
reaches nearly at zero volt because V+ is nearly equal to V- . At the same
time LED gets turned on due to formation of voltage difference between
its terminals. Resistor R4 is used to limit the flow of current through
LED .When light falls on the LDR its resistance decreases which makes
the voltage at Pin2 (V-) decreased. As we know that VO = A (V+ -- V-), due
to large value of A (open loop gain) the output voltage Vo reaches nearly
Vcc. At the same time LED gets turned off because the voltage difference
between its two terminals becomes nearly equal.
In place of LED any kind of work can be done by using low and high
voltage logic for example instead of LED a relay can be operated.
Components Required:
Op-amp# LM358;
R4# 270Ω;
LED# small or large one;
LDR# small;
R1&R2# 10KΩ;
R3# 10KΩ (Variable resistor port)
Battery# 6 Volt
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Contact us:
If you have any queries regarding the above project or you want to order the
components, you can contact us through any one of the following:
Office:
Aeronspire
Surya Vihar colony, Bartand, Dhanbad
Mob: 09031269502
www.aeronspire.com
Mail us at: info@aeronspire.com
Visit us at:
This information is provided for the understanding purpose of Op-amp as a comparator, but
without any guarantee. We disclaim any liability for the accuracy of this information. Aeronspire
and its members are not responsible for any kind of malfunction of the project or if it causes any
physical damage due to use of it or if it does not work according to the information provided
above.