Saturday, July 26, 2008

Best book for Electronics circuits

Everyone who is joining first year in BE/B.Tech degree program under Anna university affiliated colleges will have a common syllabus. And also the first year has been made non semester by Anna University. Only during the second year the students will be entering into their department. It is from the second year you will start learning your core subjects. For me being a ECE student my core subject was electronics circuit 1 and 2, I had a lot of interest in learning it but unfortunately my staff was not good which slowed me up in my core field. The best book for electronics circuits is 'Electronic Devices and Circuit Theory' by Robert L.Boylestad and Louis Nashelsky. It covers all the information about BJT, FET, CMOS, SCR, rectifiers and lots more. The book may seem to be too big but it's the best book in electronics. You can gain much knowledge from this book instead of getting a Bhakshi and mugging it up which is not going to be useful to you in anyway. If you have read this book please leave a comment about it.

Monday, July 21, 2008

Digital Logic Families

Information about digital logic families is the commonly asked question in many entrance exams for embedded training course. The most popular digital logic families are transistor-transistor logic (TTL), emitter-coupled logic (ECL), metal-oxide semiconductor (MOS) and complementary metal-oxide semiconductor. Now let us see about the features of each of these families.

  • The TTL is a logic family that has been in operation for a long time and is considered as standard. They consume more power than an equivalent CMOS device but consume less power when compared to ECL.
  • The ECL logic family has an advantage in systems requiring high speed operations. The ECL gates use differential amplifier configuration at the input state. They usually operate with negative power supplies.
  • The MOS is suitable for circuits that need high component density.
  • The CMOS is preferable in systems requiring low power consumption and they are used for VLSI design.

Saturday, July 19, 2008

Know about the various levels of Integration

There are four levels of integration in Digital ICs. You can find these details asked as viva questions in digital electronics lab. The categorization is based on the circuit complexity as measured by the number of gates in a single package. The various levels of integration are small, medium, large or very large scale integration.
  • The Small Scale Integration devices contain several independent gates in a single package. The number of gates in SSI is usually lesser than 10.
  • The Medium Scale Integration devices have about 10 to 1000 gates in a single package. They are used to perform specific elementary digital operations. They include decoders, adders and multiplexers.
  • The Large Scale Integration devices have thousands of gates in a single package. They include processors, memory chips and programmable logic devices.
  • The Very Large Scale Integration devices have hundred of thousands of gates within single package. They include large memory arrays and complex microcomputer chips.
Just leave a comment if you know additional details about the levels of integration which will be useful for the readers.

Tuesday, July 15, 2008

Know the difference between LATCHES and FLIPFLOPS

Most of you would have learned Digital Electronics in your third semester. You may have heard about these memory elements which are used for storing binary information. The latches are nothing but most basic types of flip-flops. But the latches are level sensitive whereas flip-flops are edge sensitive. This is the basic difference between the two. Thus the change of state in a latch will occur even for an active high input (dc level) i.e., the latch will respond to the change in state when the clock pulse is still in logic1 which will lead to undesirable situation. The change of state in a flip-flop occurs only when their is a change in the clock input. Since the state of a memory element must change only there is a change in control input (ac level) we use flip-flops as storage elements in digital circuits instead of latches. I hope that you can know understand the basic difference between latches and flip-flops. The below image shows the clock response in latches and flip-flops. If you know any other differences then please post a comment so that others may know about latches and flip-flops.

Saturday, July 12, 2008

My first blow

It’s true that “Failure is the stepping stone to success”. I have realized it practically when, I first started to build my electronic circuit ‘LED flasher’. I took the circuit from EFY magazine when I was in my 4th semester. It's a simple circuit using LM317 along with some resistors, capacitors, diode and LED. The output was to switch the LED ON and OFF for an interval of 15 seconds. The reason I took the ‘LED flasher’ circuit from EFY was because I was able to identify all the circuit components. After getting the required components from Ritchie street I started giving the circuit connection in my breadboard. After completing my circuit connection I checked the circuit through my multimeter and there was no problem with it. I was excited to switch ON my power supply to check my circuit, and it was time to obtain the fruit for my hard work. When I turned ON my power supply I heard the bursting sound from the circuit, it was the capacitor!! And my LED turned BLACK after glowing brightly. I was just shocked with the result of my connection trying to find out what went wrong. Then I found that I was wrong in connecting the pins of LM317. It was my first blow in my path towards electronics. A little caution could have made me attain the fruit of my hard work. But the incident was helpful to me when I started up with my other circuits. The incident made me to be more cautious when I was building other circuits. I believe that this failure has made me to succeed in my project.

Hope you would have you own blow while starting any process(in any field). Leave a comment regarding your first blow so that others can learn much from you.

Thursday, July 10, 2008

Introduction to digital circuits

Digital Circuits fall under two basic categories they are, Combinational and Sequential. The Combinational circuits are those which has no storage elements and the output of the combinational circuits depends only on the present input. The Sequential circuits on the other hand, has storage elements and their output depends on external inputs and the values in the storage elements. The sequential circuits can be further classified into Synchronous and Non synchronous.

A synchronous sequential circuit is a system whose behavior can be defined from the knowledge of its signals at discrete instants of time(clock pulses). The behavior of an asynchronous sequential circuit depends upon the input signals at any instant of time and the order in which the inputs change.

Monday, July 7, 2008

Reed Switch (sensor 1)


The reed switch is an electrical switch operated by an applied magnetic field. It consists of a pair of contacts on ferrous metal reeds in a hermetically sealed glass envelope. The contacts may be normally open, closing when a magnetic field is present, or normally closed and opening when a magnetic field is applied.
When a magnetic force is generated parallel to the reed switch, the reeds become flux carriers in the magnetic circuit. The overlapping ends of the reed become opposite magnetic poles, which attract each other. If the magnetic force between the poles is strong enough to overcome the restoring force of the reeds, the reeds will be drawn together. In our project laser based tracking system we used the reed switch for mouse click operation. Note : please be careful while bending the Reed Blade, don' t bend it near the Glass capsule, if you do so it will break. Leave about a 1cm gap and bend the Reed Blade.

Saturday, July 5, 2008

Light Dependent Resistor (sensor 2)


A LDR or photoresistor is an electronic component whose resistance decreases with the increasing incident light intensity. It can also be referred to as a photoconductor. It 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 (and its hole partner) conduct electricity, thereby lowering resistance. In short as light falls on it the resistance of LDR will decrease from normal conditions. Can be used as Night switch alarm, in counter circuit with laser beam to calculate the person entering into the door etc. LDR's of various sizes and shapes is shown below.

Wednesday, July 2, 2008

Power supply circuit

Designing a power supply circuit is one of the basic steps in any projects which you are about to start. Now let us see a +5 volt regulated power supply circuit, which i have used for my project. The circuit diagram is shown below.

The circuit includes a step down transformer and a full wave rectifier followed by a +5 volt regulator. The step down transformer steps down the ac voltage from 230 volts to 12 volt ac. After that it is passed through a full wave rectifier where we obtain an unregulated dc supply of 12 volt. The dc supply is regulated by passing through the regulator 7805. The capacitors are used to avoid ripples in the incoming voltage. The photo below shows my +5volt power supply circuit.

Note that i have included a RED LED to indicate whether the power supply is ON or OFF. I have provided a Heat sink to 7805 inorder to withdraw maximum amount of current from it. Without Heat sink we can draw current only upto 150mA.