10 Stage LED Sequencer

10 Stage LED Sequencer

LED Chaser



  • IC1- CD4017
  • IC2- NE555
  • C1 – 1μ
  • C2- 0.01 μ
  • R1 – 470 Ω
  • R2 – 100 KΩ
  • R3- 100 Ω
  • LED1-10 – RED LED
  • 9volt DC power supply.
















For power supply you can use 9 volt battery or can design separate power supply using step down transformer and 1N4007 diodes.

Variable DC Power Supply using LM317

Below is the circuit for variable dc power supply


R1- 240 Ω

R2- 5K VR

R2 can be replaced by fixed value resistor for fixed power supply. Following formula can be used to calculate output voltage.


Output voltage should be2 voltage greater than input.

Parts for current setup

  •  D1, D2 – 1N4001
  • C1-0.1 μ
  • C2 – 10 μ 50v
  • voltage regulator – LM317

20 Watt Inverter

This circuit will drive a 40 watt fluorescent or two 20-watt tubes in series. The transformer is wound on a ferrite rod 10mm dia and 8cm long. The wire diameters is 0.61mm wire for the primary and 0.28mm wire for the secondary and feedback winding.

The circuit will take approx. 1.5amp on 12v, making it more efficient than running the tubes from the mains. A normal fluorescent takes 20 watts for the tube and about 15 watts for the ballast.


Note: Do not remove the tube when the circuit is operating as the spikes produced by the transformer will damage the transistor.

Parts list

  • Transistor – BC338 and TIP 3055
  • Resistance – 47 K, 47 R, 180 R, 2R2
  • Variable Resistance – 100k
  • Capacitors – 100u 16v, 100n
  • On/Off Switch
  •  1 ferrite rod 10mm in 8mm long
  • 30 m winding wire .28mm dia
  • 4 m winding wire .61mm dia
  • 2* 20 watt tube or 1* 40 watt tube
  • 12 v DC power supply




















LED Basics

Today LED has become an integral part of consumer electronics.

LED TV, LED Display, LED Lights and so on. These are becoming very popular because of there low power consumption.

What is LED?
LED stands for Light emitting diode.

A light emitting diode is essentially a PN junction semiconductor diode that emits a monochromatic(single) colour light when operated in a forward biased direction.

For detail in technical evolution refer the following url


Early LEDs were only bright enough to be used as indicators, or in the displays of early calculators and digital watches. More recently they have been starting to appear in higher brightness applications.

LED Basics – Characteristics voltage drop

When a LED is connected around the correct way in a circuit it develops a voltage across

it called the CHARACTERISTIC VOLTAGE DROP. A LED must be supplied with a voltage that is higher than its “CHARACTERISTIC VOLTAGE”  via a resistor – called a VOLTAGE DROPPING RESISTOR or CURRENT LIMITING RESISTOR

How LED works?

LED and resistor are placed in series and connected to a voltage.As the voltage rises from 0v, nothing happens until the voltage reaches about 1.7v. At this voltage a red LED just starts to glow. As the voltage increases, the voltage across the LED remains at 1.7v but the current through the LED increases and it gets brighter. As the current increases to 5mA, 10mA, 15mA, 20mA the brightness will increase and at 25mA, it will be a maximum.

This is just a simple example as each LED has a different CHARACTERISTIC VOLTAGE DROP and a different maximum current.

In the diagram below we see a LED on a 3v supply, 9v supply and 12v supply. The current-limiting resistors are different and the first circuit takes 6mA, the second takes 15mA and the third takes 31mA. But the voltage across the red LED is the same in all cases.

LED Basics – Head Voltage

As the supply-voltage increases, the voltage across the LED will be constant at 1.7v (for a red LED) and the excess voltage will be dropped across the resistor. The supply can be any voltage from 2v to 12 or more. The resistor will drop 0.3v to 10.3v. This is called HEAD VOLTAGE.

The voltage dropped across this resistor, combined with the current, constitutes wasted energy and should be kept to a minimum.




Most supplies are derived from batteries and the voltage will drop as the cells are used.

Here is an example of a problem:
Supply voltage: 12v
7 red LEDs in series = 11.9v
Dropper resistor = 0.1v
As soon as the supply drops to 11.8v, no LEDs will be illuminated.

Example 2:
Supply voltage 12v
5 green LEDs in series @ 2.1v = 10.5v
Dropper resistor = 1.5v
The battery voltage can drop to 10.5v
Suppose the current @ 12v = 25mA.
As the voltage drops, the current will drop.
At 11.5v, the current will be 17mA
At 11v, the current will be 9mA
At 10.5v, the current will be zero

Many batteries drop 1v and still have over 80% of their energy remaining. That’s why you should design your circuit to have a large HEAD VOLTAGE.

Some Basic circuits using LED

1. Polarity Tester


2. Continuity Tester


3. USB Reading Lamp



Basic Power supply circuits Part 1

To understand power supply circuits, we need to understand rectifiers.

A rectifier converts AC or alternating current to DC direct current. Rectifiers are used in Power supply circuits which we will discuss in detail.

The process of converting AC to DC is called Rectification.

Half wave rectification.

It requires only single diode. Only positive cycle of the current is passed through the diode i.e only half of the AC wave is passed and hence the name half wave.

Half wave rectifier

Full Wave rectification

It requires 2 diodes or 4 diodes. In this both positive and negative AC cycle is passed through the diode alternatively.

Full wave rectifier

Bridge Rectifier

Bridge rectifier also produces same output as full wave rectifier.

Bridge rectifier

The four diodes D1-D4 are arranged in series pair with only 2 diodes conducting current during each positive half cycle.
During the positive half cycle of the supply, diode D1 and D2 conduct in series while diodes D3 and D4 are reverse biased.


During the negative half cycle of the supply, diode D3 and D4 conduct while D1 and D2 are reverse biased.


In the next article I will show how to use rectifiers to build DC power supply circuits.

Basic Electronics – 2

Passive Components


To oppose the flow of electrons ( current). The symbols are shown below.

Resistance is measured in units called “Ohm”. 1000 ohms is shown as 1k ohm (103 ohm) and 1000 k ohm is shown as M.ohms (106ohm).

Resistors can be broadly of two types.

• Fixed Resistors and Variable Resistors.

Fixed Resistors:

Carbon Film (5%, 10% tolerance) and Metal Film Resistors (1%,2% tolerances) and wire wound

resistors. A fixed resistor is one for which the value of its resistance is specified and cannot be varied in general.

Resistance Value

The resistance value is displayed using the color code ( the colored bars/the colored stripes), because the average resistor is too small to have the value printed on it with numbers. The resistance value is a discrete value.

For example, the values [1], [2.2], [4.7] and [10] are used in a typical situation.

Types of Resistance


This is the most general purpose, cheap resistor. Usually the tolerance of the resistance value is ±5%. Power ratings of 1/8W, 1/4W and 1/2W are frequently used. The disadvantage of using carbon film resistors is that they tend to be electrically noisy.


Metal film resistors are used when a higher tolerance (more accurate value) is needed. Nichrome(Ni-Cr) is generally used for the material of resistor. They are much more accurate in value than carbon

film resistors. They have about ±0.05% tolerance.


There is another type of resistor called the wire wound resistor. A wire wound resistor is made of metal

resistance wire, and because of this, they can be manufactured to precise values. Also, high-wattage resistors can be made by using a thick wire material. Wire wound resistors cannot be used for high-frequency circuits.

Ceramic Resistor

Another type of resistor is the Ceramic resistor. These are wire wound resistors in a ceramic case, strengthened with a special cement. They have very high power ratings, from 1 or 2 watts to dozens of watts. These resistors can become extremely hot when used for high power applications, and this must be taken into account when designing the circuit.


It is made with many resistors of the same value, all in one package. One side of each resistor is connected with one side of all the other resistors inside. One example of its use would be to control the current in a circuit powering many light emitting diodes (LEDs). The face value of the resistance is printed.


The 4S indicates that the package contains 4 independent resistors that are not wired together inside. The housing has eight leads instead of nine.


There are two general ways in which variable resistors are used. One is the variable resistor whose value is easily changed, like the volume adjustment of Radio. The other is semi-fixed resistor that is not meant to be adjusted by anyone but a technician. It is used to adjust the operating condition of the circuit by the technician.

Semi-fixed resistors are used to compensate for the inaccuracies of the resistors, and to fine-tune a circuit. The rotation angle of the variable resistor is usually about 300 degrees. Some variable resistors must be turned many times( multi-turn Pot) to use the whole range of resistance they offer.

This allows for very precise adjustments of their value. These are called “Potentiometers” or “Trimmer Potentiometers” or “presets”.


Some components can change resistance value by changes in the amount of light falling on them. One type is the Cadmium Sulfide Photocell. It is a kind of resistor, whose value depends on the amount of light falling on it. When in darkness its resistance if very large and as more and more light falls on it its resistance becomes smaller and smaller.

There are many types of these devices. They vary according to light sensitivity, size,  resistance value etc.


They are thermally sensitive resistor. The resistance value of the thermistor changes according to temperature. They are used as a temperature sensor. There are generally two types of thermistors, with Negative Temperature Coefficient(NTC) Positive Temperature Coefficient(PTC). The resistance of NTC thermistors decreases on heating while that of PTC thermistors increases.


For example, to power a 3V circuit using a 12V supply, using only a resistor, then we need to calculate the power rating of the resistor as well as the resistance value. The current consumed by the 5V circuit needs to be known.

Assume the current consumed is 250 mA (milliamps) in the above example. That means 9V (=12-3 V) must be dropped with the resistor. The resistance value of the resistor becomes 9V / 0.25A = 36(ohm).

The consumption of electric power for this resistor becomes 0.25A x 0.25A x 36ohm = 2.25W. Thus the selection of resistors depends on two factors namely tolerance and electric power ratings.


Important and useful law.The current(I) flowing through a conductor is proportional to the voltage (V) applied across its ends. This can be written in algebraic form as V ∝ I Or V = IR where R is the proportionality constant. R is called Resistance and is measured in ‘Ohms’ ( Ω ).

Usually resistors are also specified in circuits in kilo Ohms(kΩ) and Mega Ohms(MΩ). The other useful relationships are V = RI, and R=V/I.

Basic Electronics – 1


Electronic component can be divided into 2 types: Active and Passive components

Resistors and Capacitors etc. are known as passive components because they can only attenuate the electrical voltage and signals and cannot amplify.

Devices like transistors and operational amplifier(op Amps)can amplify or increase the amplitude and energy associated with the signals and so are termed as Active components.

Apart from components and circuits we must also have familiarity with some of the essential electronic measuring instruments like multimeter, regulated power supplies, function generators and oscilloscopes etc.

Basic electronics - Part 1