**LDR circuit symbols**

**Enclosed LDR**

Typical LDR resistance vs light intensity graph

The most common type of LDR has a resistance that falls with an increase in the light intensity falling upon the device (as shown in the image above). The resistance of an LDR may typically have the following resistances:

Daylight = 5000Ω = 5kiloΩ = 5kΩ

5k for short. This may vary from design to design.

Dark = 20000000Ω =20Mega Ω = 20MΩ

This goes to show that there is a large variation between these figures. If you plotted this variation on a graph you would get something similar to that shown by the graph shown above.

**Applications of LDRs**

There are many applications for Light Dependent Resistors. These include:

**1. Lighting switch**

The most obvious application for an LDR is to automatically turn on a light at a certain light level. An example of this could be a street light or a garden light.

**2. Camera shutter contro****l**

LDRs can be used to control the shutter speed on a camera. The LDR would be used to measure the light intensity which then adjusts the camera shutter speed to the appropriate level.

**A typical LDR controlled transisto**r *circuit*

The circuit shown above shows a simple way of constructing a circuit that turns on when it goes dark. In this circuit the LDR and the other Resistor form a simple ‘Potential Divider’ circuit, where the centre point of the Potential Divider is fed to the Base of the NPN Transistor.

When the light level decreases, the resistance of the LDR increases. As this resistance increases in relation to the other Resistor, which has a fixed resistance, it causes the voltage dropped across the LDR to also increase. When this voltage is large enough (0.7V for a typical NPN Transistor), it will cause the Transistor to turn on.

The value of the fixed resistor will depend on the LDR used, the transistor used and the supply voltage.

Please read to our blog on resistors in series and parallel to understand the circuit above more.

“

a normal PC – generally in some variation of ” C”.

Arduino is an open source hardware and software project, created to be as simple as possible. Arduino is not some hardware you should be afraid of. It comes in a variety of flavors and sizes. It is used by artists, hackers, hobbyists, and professionals to easily design, prototype and experiment with electronics. Use it as brains for your robot, to build a new digital music instrument, or to make your house plant tweet you when it’s dry. An Arduino contains a microchip, which is a very small computer that you can program. You can attach sensors to it so that it can measure conditions (like how much light there is in the room). It can control how other objects react to those conditions (room gets dark. LED turns on).

The project is based on microcontroller board designs, produced by several vendors, using various microcontrollers. Microcontrollers use inputs and outputs like any computer. Inputs capture information from the user or the environment while outputs do something with the information that has been captured. A switch and a sensor could be a digital and an analog input respectively into the Arduino. Any object we want to turn on and off and control could be an output. It could be a motor or even a computer. These systems provide sets of digital and analog input/output (I/O) pins that can interface to various expansion boards, which are often called “*shields”,* and other circuits. The boards feature serial communication interfaces, including Universal Serial Bus (USB) on some models, for loading programs from personal computers. For programming the microcontrollers, the Arduino project provides an integrated development environment(IDE) based on a programming language named *Processing*, which also supports the languages C and C++. The Arduino language is very similar to C. It’s almost the same language but Arduino provides us with several libraries to make things a bit easier.

Reference:https://en.wikipedia.org/wiki/Arduino

]]>- Thermistor actually means thermal resistor.

So, there are basically two types of thermistors, which are:

and**NTC****PTC**

means*NTC***N**egative**T**emperature**C**o-efficient, and its resistance varies inversely proportional to the applied temperature.on the other Hand is**PTC****P**ositive**T**emperature**C**o-efficient as its resistance varies directly proportional to the applied temperature.

* Thermistors* when connected in series with a resistor gives a corresponding change in voltage whenever the temperature is changed. This could be used to monitor the temperature of the thermistor surrounding by merely measuring the voltage across the thermistor.

section we’ll evaluate how Ohm’s law is applied to produce the voltage divider equation. This is a fun exercise.

If you are interested, prepare for some tours with Ohm’s law and algebra.

Voltage Divider formula Derivation

Evaluating the circuit

So, what if you wanted to measure the voltage at Vout ?

Let’s assume that we know the

values of V , R1, and R2 , so let’s get our Vout equation in terms of those values.

Let’s start by referring to the currents in the circuit, I1 and

I2 –which we shall call the currents through the respective resistors.

Our goal is to calculate Vout , what if we applied Ohm’s law to that voltage? Easy enough, there’s just one resistor and one current involved:

Vout = I2 * R2

Sweet! Right?! We know R2 ’s value, but what about I2 ? That’s an unknown value, but we do know a little thing about it. We can assume (and this turns out to be a big assumption) that I1 is equivalent to I2 .

*Alright, but does that help us?*

**Hold that thought. **

Our circuit now looks like this, where I equals both I1 and I2 .

What do we know about Vin? Well, Vin is the voltage across both resistors R1 and R2 . Those resistors are in series.

Series resistors add up to one value, so we could say: R =R1+R2

*And, for a moment, we can simplify the circuit to:*

Common Current

Ohm’s law at its most basic!

*V = I * R. *

Which, if we turn that R back into R1 + R2 , can also be written as:

*I = Vin / (R1+R2)*

And since I1 is equivalent to I2 , plug that into our Vout equation to get:

*Vout = R2 * (Vin/R1+R2)*

This is so by just replacing ** I** with Vin/(R1+R2) . And that,

output voltage is a fraction of the input voltage, and that fraction is R2 divided by the sum of R1 and R2.

Expect tutorials on sensors based on this voltage divider principle soon.

See you then and please do not forget to leave us a comment

]]>Voltage Divider rule

The voltage divider rule is very simple and shows that the output voltage *Vout* is a fraction of the input voltage *Vin*, and the voltages across the resistors divide in ratio to their values.

In electronics , a voltage divider (also known as a potential divider ) is a passive linear circuit that produces an output voltage ( V out ) that is a fraction of its input voltage (V in ). Voltage division is the result of distributing the input voltage among the components of the divider. A simple example of a voltage divider is two resistors connected in

series as shown above, with the input voltage applied across the resistor

pair and the output voltage emerging from the connection

between them.

A voltage divider is a simple circuit which turns a large voltage into a smaller one. Using just two series resistors and an input voltage, we can create an output voltage that is

a fraction of the input. Voltage dividers are one of the most fundamental circuits in electronics. If learning Ohm’s law was like being introduced to the * ABC’s*, learning about voltage dividers would be like learning how to spell

There are two important parts to the voltage divider:

1. The circuit and

2. The equation.

A voltage divider involves applying a voltage source across

a series of two resistors. You may see it drawn a few

different ways, but they should always essentially be the

same circuit.

Examples of voltage divider circuit are as shown below and they are basically the same.

We’ll call the resistor closest to the input voltage (Vin ) R1, and the resistor closest to ground R2 . The voltage drop across R2 is called Vout , that’s the divided voltage our circuit exists to make.

That is all there is to the circuit! Vout is our divided voltage. That is what will end up being a fraction of the input voltage.

The voltage divider equation assumes that you know three values of the above circuit: the input voltage (V in), and both resistor values (R1 and R2 ). Given those values, we can use

this equation to find the output voltage (V out):

Voltage Divider formula

*Memorize they equation!*

This equation states that the output voltage is directly proportional to the input voltage and the ratio of R1 and

R2 .

If you would like to find out where this comes from, check it out on busybrained.com/?p=70 where the equation is derived. But for now, just write it down and remember it!

Resistor voltage dividers are commonly used to create reference voltages, or to reduce the magnitude of a voltage so it can be measured, and may also be used as signal attenuators at low frequencies. For direct current and relatively low frequencies, a voltage divider may be

sufficiently accurate if made only of resistors.

*Please do not forget to leave us a comment.*

**Volt age**

Voltage is how much energy is between two points on a circuit. These two points have different charges, one is higher and the other is lower. The difference between these

two points of the charge is how we measure the voltage.

In other words, voltage is the driving force in electrical circuit.

The unit of “volt” is the name of the Italian physicist Alessandro Volta who created the first chemical battery. The letter “V” represents voltage.

**Current**

Current is how fast the charge is flowing. The higher the charge, the faster the current. Current has to do with electrons flowing in a circuit. ** Current** measures how fast

the electrons go.

The unit of the current is “**ampere**,” and usually, a person writes it as “

*Resistance*

Resistance is how much the circuit resists the flow of the charge. This makes sure the charge does not flow too fast and damage the components. In a circuit, a light bulb can be a resistor. If electrons flow through the light bulb, then the light bulb will light up. If the resistance is high, then the lamp will be dimmer. The unit of resistance is “* Ω*”, which is called omega, and pronounced “

You could visit busybrained.com/?p=40 for extensive analysis on resistor and its resistance.

Ohm’s law states that the electrical current (I) flowing in an circuit is proportional to the voltage (V) and inversely proportional to the resistance (R) so long as the temperature and other factors are kept constant.

Therefore, if the voltage is increased, the current will increase provided the resistance of the circuit does not change.

To make a current flow through a resistance there must be a voltage across that resistance. Ohm’s Law shows the relationship between the voltage (V), current (I) and resistance (R).

Ohm’s Law can be written three ways:

1. **V = I*R**

2. * I = V/R *and

3. **R = V/I**

where:

V = voltage in volts (V)

I = current in amps (A)

R = resistance in ohms (Ω)

Use this method to guide you through calculations:

. Write down the Values , converting units if necessary.

. Select the Equation you need

. Put the Numbers into the equation and calculate the answer.

It should be very Easy now! See the examples below:

3V is applied across a 6Ω resistor, what is the current?

Values: V = 3V, I = ?, R = 6Ω

Equation: I = V / R

N umbers: Current, I = 3 /6 = 0.5A

A lamp connected to a 6V battery passes a current of 60mA,

what is the lamp’s resistance?

Values: V = 6V, I = 60mA, R = ?

Equation: R = V /I

Numbers: Resistance, R = 6 / 60 = 0.1k = 100

(using mA for current means the calculation gives the

resistance in k )

A 1.2k resistor passes a current of 0.2A, what is the

voltage across it?

Values: V = ?, I = 0.2A, R = 1.2k = 1200Ω

(1.2k is converted to 1200Ω because **A** and **k** must not be used together)

Equation: V = I × R

Numbers: V = 0.2 × 1200 = 240V

Considering the photo below, the ** VOLT** pushes the

The simplest combinations of resistors are the series and parallel connections illustrated below.

The total resistance of a combination of resistors depends on both their individual values and how they are connected.

(1.) A series connection of resistors.

(2.) A parallel connection of resistors.

__Resistors in Series__

When are resistors in series ? Resistors are said to be connected in series when they are daisy chained together in a single line resulting in a common current flowing through them. More so resistors are said to be in series whenever the flow of current is sequential through the device. For example, if current flows

through resistors R_{1}, then R_{2}and R_{3}as shown below.

Resistors in series can be added with simple arithmetical addition.

R_{1} + R_{2} + R_{3} = R_{s}

It seems reasonable that the total resistance is the sum of the individual resistances, considering that the current has to

pass through each resistor in sequence.

*Resistors in parallel*

The diagram above shows resistors in parallel, wired to a voltage source. Resistors R_{1} and R_{2} are in parallel as each resistor is connected directly to the voltage source by connecting wires with negligible resistance. Each resistor thus has the full voltage of the source applied to it.

Each resistor draws the same current it would if it alone were connected to the voltage source

(provided the voltage source is not overloaded).

The effective resistance, Rs of paralleled Resistors is given as,

1/Rs= 1/R1+1/R2+1/R3

These analyses of series and parallel connections of Resistors will go a long way in helping us to understand working principles of some sensors like thermistor, LDR and others.

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