FLASHING LED

This is a simple LED project for starters and one of the first LED project that I did .It will make the LED flashing at the rate I decide . I had lot of fun doing this one , every time I changed the value of resistor or capacitor , LED keep changing the time between flashing . Let’s build this thing.

Connection :-

1 . Connect pin 2 and pin 6 of 555 IC
2 . Connect pin 4 and Pin 8 of 555 IC
3 . Connect 47mF capacitor +ve ( longer leg ) to pin 2 and -ve to ground.
4 . Connect +ve (longer leg leg ) of LED to pin 3 and -ve to pin 1
5 . Now connect one of the 10k resistor between pin 8 and pin 7
6 . Now connect other 10k resistor between pin 7and pin 6
7. Finish the circuit with battery connection , +ve to pin 8 and -ve to pin 1

If you have problem in identifying the pins of 555 timer IC checkout my post on the 555 timer IC which helps to identify the pins and the function of each pins.

If your connection are correct LED Will be flashing . If you are haveing problem with circuit , leave a comment and I Will help you.

Components Required :-

1. Resistor – 10k x 2
2. Capacitor – 47mF
3. White LED
4. 555 IC
6. Wire
7. 9V battery

SIMPLE TRANSISTOR CIRCUIT

This is the simplest circuit you can make with a transistors. You can use any NPN transistors. Here I have used BC 547. In this  project the transistor is turned on via a finger.

Connect the LED, 220 ohm resistor and transistor as shown in the circuit. Touch the top point with two fingers of one hand and the lower point with fingers of the other hand and squeeze. As you press harder, the resistance of your finger decreases. This allows more current to flow into the base and the transistor turns on more and more. Your body has resistance and when a voltage is present, current will flow though your body (fingers). The transistor is amplifying the current through your fingers and this is enough to illuminate the LED.

If you have trouble in identifying the base, emitter, and collector check out my post on the BJT.

CONNECTION

1. Connect emitter (E) of the transistor to negative terminal of battery.
2. Resistor:- Connect the resistor between the collector (C) and negative of the LED
3. Now connect the positive terminal of both LED and battery.
4. Now connect the touch wire and if you touch those wire LED glow.

COMPONENTS REQUIRED :

1. BC 547 Transistor
2. 220R Resistor
3. LED
4. Battery

To make sure this is working simply press on the two wires and the LED will illuminate brighter and if not leave a comment and I will help you.

SIMPLE SECURITY

This is the simple security system that you can build for your own.You have already seen in movies , somebody cross the red laser line the alarm starts. You can build something like that for your own room.

Here I have placed a buzzer but you can also place a LED or other small project.

SETUP FOR THIS PROJECT :-

For setup your security all you have to do is, put a laser (I recommend laser) or a light source such as LED on one end of the door and place the LDR on other end in such a way that laser beam falls on LDR. This project work on the simple principle that, as someone enter your room the laser beam is cutoff. LDR detect this (absence of light) and trigger the buzzer.

CONNECTIONS :-

1. Place the LDR between base and emitter of transistor.
2. Connect a 10k resistor between base and +ve terminal of buzzer.
3. Connect -ve of buzzer to collector of transistor.
4. Now connect +ve of battery to +ve of buzzer and -ve of battery to emitter of transistor.

COMPONENTS  REQUIRED :-

1.BC547 transistor
2.10k resistor
3. LDR
4. Buzzer
5. Battery

CONNECTING LED PROPERLY

It’s important to connect a LED the correct way in a circuit because LED shows the output in many of the circuit that we are going to discuss. LED is simple to connect – once you know how.
I thought that it is important for starters to connect a LED in the proper way. This post is only to show how a LED can be connected to batteries without damaging it.

Let’s look into three example of connecting LED. I took these three example because all three situation can happen when you start your electronic journey.LED not glowing. LED gets damaged connecting to some batteries. Don’t know which resistor should be connected to which LED and to what battery. This all happened to me when I was 7-8 years old. I hope you don’t have any problem connecting LED after reading this post. Let’s get started.

Before connecting LED you must remember that LED must have a resistor to limit the current. It does not matter if the resistor is connected above or below the LED. The circuits are the SAME. If you have problem in identifying the positive and negative terminal of LED check out my Light Emitting Diode (LED) post

The LED in the first diagram (A) does not illuminate because a red LED requires 1.7v and the cell only supplies 1.5v.

The red LED in the second diagram (B) is damaged because it requires 1.7v and the two cells supply 3v.

To connect a red LED properly, resistor is needed to limit the current to about 25mA and also the voltage to 1.7v, as shown in the third diagram (C) as a result LED glow.

Here is little something for clearing you doubts about what if I change the value of the resistor, LED and battery. Here I have given some common LED and how to connect it to different voltages.

Red super bright (1.85V 20mA)
9V – 360R
7.5V – 280R
6V – 210R
4.5V – 130R
3V – 60R

Red bright (2.0V 10mA)
9V – 700R
7.5V – 550R
6V – 400R
4.5V – 250R
3V – 100R

Green standard (2.2V 10mA)
9V – 680R
7.5V – 530R
6V – 380R
4.5V – 230R
3V – 80R

Super blue (3.6V 20mA)
White cool (3.6V 20mA)
9V – 270R
7.5V – 190R
6V – 120R
4.5V – 40R

Orange standard (2.1V 10mA)
Yellow standard (2.1V 10mA)
9V – 690R
7.5V – 540R
6V – 390R
4.5V – 240R
3V – 90R

Blue high intensity (4.5V 20mA)
9V – 220R
7.5V – 150R
6V – 70R

Remember this voltage we apply (Vcc) must be greater than voltage drop of LED, this is the reason why some LED won’t work on 3V.

If you want to know more about LED check out my Light Emitting Diode (LED) post.
Feel free to comment.

THE 555 TIMER IC PINOUT

The 555  timer IC is an integrated circuit (chip) used in a variety of timer, pulse generation, and oscillator applications. The 555 can be used to provide time delays, as an oscillator, and as a flip-flop element. The primary purpose of the 555 timer is the generation of accurately timed single pulse or oscillatory pulse waveforms. The 555 has three main operating modes Monostable, Astable, and Bistable. Each mode represents a different type of circuit that has a particular output. I will make a post on the 555 main three operating modes later.

THE FUNCTION OF EACH PINS

Pin 1 Ground [GND] – Most negative supply connected to the device, normally this is common ground (0V).

Pin 2 Trigger [TRIG] – Detects 1/3 of rail voltage to make output HIGH.

Pin 3 Output [OUT] – The 555 timer output signal pin.

Pin 4 Reset [RES] – reset. Must be taken below 0.8v to reset the chip

Pin 5 Control [CON] – A voltage applied to this pin will vary the timing of the RC network

Pin 6 Threshold [THRESH] – Detects 2/3 of rail voltage to make output LOW only if pin 2 is HIGH

Pin 7 Discharge [DIS] – Goes LOW when pin 6 detects 2/3 rail voltage but pin 2 must be HIGH.

Pin 8 VCC [VCC] – Most positive supply connected to device, normally this is 5V, 10V or 15V.

555 IC PINOUT

To identify the Pin1, place the 555 on a flat surface such a way that the small circle is in the top left corner.Now identification of pins are easy. Now start from the top left corner (where the small circle is) first pin is pin1, next pin below is pin2, next pin below is pin3, next pin below is pin4, pin5 is on the bottom right corner, next pin above is pin6, next pin above is pin7, next pin above is pin8.

To identify the pins of IC start from the top left corner where the small circle is and the top first pin will be pin1 and start counting in the pins in anticlockwise direction pin 2, pin 3, pin 4….and stop at the first pin on the top right corner which in the case of 555 is pin 8.

Here I have marked the 8 pins on a 555 iC:-

For the easy understanding of the circuit we always draw the 555 as a building block, as shown below with the pins in the following locations. I have given functions of each pin next to it. So you can remember it easily. I hope you can understand it.

If you have doubt in identify the pins of 555 IC OR function of each pin, put it in the comments and I will help you to solve it.

TRANSISTOR

The transistor is the fundamental building block of modern electronic devices.A transistor is a semiconductor device used to amplify and switch electronic signals and electrical power. It is composed of semiconductor material with at least three terminals for connection to an external circuit. The vast majority of transistors are now produced in integrated circuits (often shortened to IC, microchips or simply chips) and along with other electronic components. A logic gate consists of up to about twenty transistors whereas an advanced microprocessor, can use as many as billions of transistors

SIMPLIFIED OPERATION

The essential usefulness of a transistor comes from its ability to use a small signal applied between one pair of its terminals to control a much larger signal at another pair of terminals. A transistor can control its output in proportion to the input signal; that is, it can act as an amplifier. Alternatively, the transistor can be used to turn current on or off in a circuit as an electrically controlled switch, where the amount of current is determined by other circuit elements.

TRANSISTOR AS A SWITCH

Transistors are commonly used as electronic switches, both for high-power applications such as switched-mode power supplies and for low-power applications such as logic gates.

In any switching circuit, values of input voltage would be chosen such that the output is either completely off, or completely on. The transistor is acting as a switch, and this type of operation is common in digital circuits where only “on” and “off” values are relevant.

TRANSISTOR AS AN AMPLIFIER

Various configurations of single transistor amplifier are possible, with some providing current gain, some voltage gain, and some both. From mobile phones to televisions, vast numbers of products include amplifiers for sound reproduction, radio transmission, and signal processing

The amplifier is designed so that a small change in current through the base of the transistor; (the transistor amplify the current) and produce large output

ADVANTAGES

The key advantages that have allowed transistors to replace their vacuum tube predecessors in most applications are

No power consumption by a cathode heater.
Small size and minimal weight, allowing the development of miniaturized electronic devices.
Low operating voltages compatible with batteries of only a few cells.
No warm-up period for cathode heaters required after power application.
Lower power dissipation and generally greater energy efficiency.
Higher reliability and greater physical ruggedness.
Extremely long life. Some transistorized devices have been in service for more than 50 years.
Insensitivity to mechanical shock and vibration, thus avoiding the problem of microphonics in audio applications.

LIMITATIONS

Silicon transistors can age and fail.
High-power, high-frequency operation, such as that used in over-the-air television broadcasting, is better achieved in vacuum tubes due to improved electron mobility in a vacuum.
Solid-state devices are more vulnerable to Electrostatic discharge in handling and operation
A vacuum tube momentarily overloaded will just get a little hotter; solid-state devices have less mass to absorb the heat due to overloads, in proportion to their rating
Sensitivity to radiation and cosmic rays. Vacuum tubes create a distortion, the so-called tube sound, that some people find to be more tolerable to the ear.

TYPES

Transistors are categorized by
1. Structure: BJT, JFET, IGFET (MOSFET), insulated-gate bipolar transistor.
2. Electrical polarity (positive and negative): n–p–n, p–n–p (BJTs); n-channel, p-channel (FETs)
3. Maximum power rating: low, medium, high
4. Maximum operating frequency: low, medium, high, radio (RF), microwave frequency
5. Application: switch, general purpose, audio, high voltage, super-beta, matched pair

BJT – NPN AND PNP TRANSISTORS

A bipolar junction transistor (BJT or bipolar transistor) is a type of transistor that relies on the contact of two types of semiconductor for its operation. BJTs can be used as amplifiers, switches, or in oscillators. BJTs can be found either as individual discrete components, or in large numbers as parts of integrated circuits.

Bipolar transistors are so named because their operation involves both electrons and holes. These two kinds of charge carriers are characteristic of the two kinds of doped semiconductor material
The BJT has three leads for connection which are called as emitter, collector, and base. Most of the BJT collector current is due to the flow of charges injected from a high-concentration emitter into the base where there are minority carriers that diffuse toward the collector, and so BJTs are classified as minority-carrier devices.

STRUCTURE

A BJT consists of three differently doped semiconductor regions, the emitter region, the base region and the collector region. These regions are, respectively, p type, n type and p type in a PNP transistor, and n type, p type and n type in an NPN transistor. Each semiconductor region is connected to a terminal, appropriately labeled: emitter (E), base (B) and collector (C). The base is physically located between the emitter and the collector and is made from lightly doped, high resistivity material

TYPES OF BJT

BJTs come in two types, known as PNP and NPN based on the doping types of the three main terminal regions. An NPN transistor comprises two semiconductor junctions that share a thin p-doped anode region, and a PNP transistor comprises two semiconductor junctions that share a thin n-doped cathode region.

NPN TRANSISTOR

NPN is one of the two types of bipolar transistors, consisting of a layer of P-doped semiconductor (the base, middle layer) between two N-doped layers. A small current entering the base is amplified to produce a large collector and emitter current. That is, when there is a positive potential difference measured from the emitter of an NPN transistor to its base (i.e., when the base is high relative to the emitter) as well as positive potential difference measured from the base to the collector, the transistor becomes active. In this “on” state, current flows between the collector and emitter of the transistor. Most of the current is carried by electrons moving from emitter to collector as minority carriers in the P-type base region. To allow for greater current and faster operation, most bipolar transistors used today are NPN because electron mobility is higher than hole mobility.

THE SYMBOL OF NPN BJT

.

PNP TRANSISTOR

The other type of BJT is the PNP, consisting of a layer of N-doped semiconductor between two layers of P-doped material. A small current leaving the base is amplified in the collector output. That is, a PNP transistor is “on” when its base is pulled low relative to the emitter.
The arrows in the NPN and PNP transistor symbols are on the emitter legs and point in the direction of the conventional current flow when the device is in forward active mode.

THE SYMBOL OF PNP BJT.

CONNECTING BJT

The bipolar junction transistor, unlike LED, capacitor or resistor, it have three legs called as emitter (E), base (B) and collector (C). This means that interchanging the collector and the emitter of the transistor may leave the circuit not working.

CONNECTING NPN BJT
                                                     
I have marked the  collector (C), base (B) and emitter (E) pins on a real NPN BJT and also on the symbol

CONNECTING PNP BJT

I have marked the  emitter (E), base (B) and collector (C) pins on a real PNP BJT and also on the symbol

LIGHT DEPENDENT RESISTOR (LDR)

A light dependent resistor (LDR) or photoresistor or photocell is a resistor whose resistance decreases with increasing incident light intensity. Below I have shown LDR in different size (small to big).

In other words, LDR is a resistor whose resistance can be adjusted by the amount of light falling on it.

A photoresistor is made of a high resistance semiconductor. If light falling on the device is of high enough frequency, photons absorbed by the semiconductor give bound electrons enough energy to jump into the conduction band. The resulting free electron conduct electricity, thereby lowering resistance.

APPLICATIONS

Photoresistors can be found when we need to control some device with the variation in light.
Photoresistors come in many types. Inexpensive cadmium sulphide cells can be found in many consumer items such as camera light meters, street lights, clock radios, alarm devices, outdoor clocks, solar street lamps and solar road studs, etc.

SYMBOL OF LDR

CONNECTING LDR

LDR is also a two-terminal electrical which can be connected either way, that means it have no positive and negative terminal.

CAPACITOR

A capacitor is a two-terminal electrical component used to store energy electro statically in an electric field. When there is a potential difference across the conductors, an electric field develops across the dielectric, causing positive charge to collect on one plate and negative charge on the other plate. Energy is stored in the electrostatic field. In order to maximize the charge that a capacitor can hold, the dielectric material needs to have as high a permittivity as possible, while also having as high a breakdown voltage as possible.

In other words the capacitors act as a local reserve for the DC power source, and bypass AC currents from the power. Different types of capacitor is shown below

WHAT IS CAPACITANCE?

Capacitance is the ratio of the electric charge on each conductor to the potential difference between them. The SI unit of capacitance is the farad, which is equal to one coulomb per volt. An ideal capacitor is wholly characterized by a constant capacitance C, defined as the ratio of charge ±Q on each conductor to the voltage V between them.

CAPACITOR TYPES

Capacitors are available commercially in many different forms. Values range from very low picofarad range (ceramic capacitors) to about 5 kF (super capacitors).

CAPACITOR MARKINGS

Most capacitors have numbers printed on their bodies to indicate their electrical characteristics. Larger capacitors like electrolytic ones usually display the actual capacitance together with the unit (for example, .22 μF / 63V).

READING VALUE OF A CERAMIC CAPACITOR

Due to the smaller sizes of ceramics capacitors, there will be only three numbers and a letter, where the numbers show the capacitance in pF

Let’s calculate the value of the ceramic capacitors shown below

Calculated as XY × 10^Z for the numbers XYZ and the letter indicates the tolerance.

A capacitor with the text 104K on its body has a capacitance of 10× 10⁴ pF = 100 nF

APPLICATIONS

Energy storage
A capacitor can store electric energy when disconnected from its charging circuit, so it can be used like a temporary battery.

Capacitors are commonly used in electronic devices to maintain power supply while batteries are being charged.

In car audio systems, large capacitors store energy for the use of amplifier on demand.
The capacitors act as a local reserve for the DC power source, and bypass AC currents from the power.

CONNECTING CAPACITOR

A capacitor is a two-terminal electrical component.

The ceramic capacitors can be connected either way, that means it have no positive and negative terminal. The symbol used for the ceramic capacitors in a circuit diagram is:-

The electrolytic capacitors have a positive terminal (longer leg) and negative terminal (shorter leg) like one I marked below

The symbol used for the electrolytic capacitors in a circuit diagram is:

HAZARDS AND SAFETY

Capacitors may retain a charge long after power is removed from a circuit; this charge can cause dangerous or even potentially fatal shocks or damage connected equipment. So handle higher value capacitor with care.

RESISTOR

WHAT IS A RESISTOR?

A resistor is an electrical component that limits or regulates the flow of electrical current in an electronic circuit and can be used to provide a specific voltage for an active device. The higher the   resistance of the resistor the smaller the current flows. A resistor look like this :-

HOW DOES RESISTOR REGULATE CURRENT?

If you connect a LED directly to a 9V battery, LED gets damaged and no longer works. But if you connect a resistor between the positive terminal of battery and LED, LED glows without damaging it. This shows us that the resistor regulate current flowing through it.

WHAT IS OHM (Ω)?

The ohm (Ω) is the SI unit of electrical resistance. An ohm is equivalent to a volt per ampere.

CONVERSION

1 mΩ = 10⁻³ Ω
1 kΩ = 10³ Ω
1 MΩ = 10⁶ Ω

SYMBOL FOR RESISTOR

Both symbols below are used to represent resistor in a circuit diagram. You can use any one of the two symbols.

CONNECTING RESISTOR

A resistor is a two-terminal electrical component like the one below

Resistor can be connected either way, that means it have no positive and negative terminal.

WHAT IS RESISTANCE?

The definition of resistance is based upon the Ohm’s law given by the German physicist Georg Simon Ohm. The Ohm’s Law states that the voltage [V] across a resistor is directly proportional to the current [I] flowing through it. Here, its resistance [R] is the constant of proportionality. Therefore,
                                    
                                 V = I * R