Showing posts with label Electronics. Show all posts
Showing posts with label Electronics. Show all posts
Friday, March 1, 2013
Causal and Non-Causal Systems Better Explained
18 comments:
Labels:
Electronics,
Explanations,
Mathematics
You must have come across causal and non-causal systems at some point in your Engineering life. Most of us might have simply studied that Causal systems are those systems which respond only to present and past inputs whereas Non-Causal systems can also respond to future inputs. That is correct but there is a lot more to explore about it. In this article we shall discuss the fundamental ideas and philosophies involved in this concept. I am not explaining the mathematics of causal systems here as they are readily found in any related text book and also on the Internet. You may refer to your text books any other source if you do not know what it is. Let us explore more on this. Causality
What is a causal system?
A system is said to be causal if the output of the system depends only on past or present values of the inputs but not on future values of the inputs.
Understanding a Causal System
The term "causal" is derived from the word cause. The cause is anything that gives rise to an action, phenomenon or condition (according to English dictionary). By the meaning of cause, we can understand that cause is nothing but an input. So it is understood that a causal system is the one which responds to a cause. The cause is the input of the system and the response is the output of the system. That means, if a system produces an output only because of events (causes or inputs or excitations) that have happened in the past or happening now, such systems are called as causal systems. Causal systems are also called non-anticipative systems.
Most (almost all) of the systems that we see in our daily life are all causal systems. Your mobile phone is a causal system because it rings only for the current call but it cannot ring for a call that may happen tomorrow. Examples are too many for causal systems because most of the systems that exist and that we see in our daily life fall into this category. Even we humans are causal systems. Our present actions (outputs) depend on the events (inputs) that have happened to us in the past and the events that are happening now but we cannot respond to events which will happen tomorrow. We may sometimes respond to events that we expect them to happen in future. But we can never respond to events that have happened in the future. Also, our expectation of the future is based on our past and present experiences. So, we are not that powerful enough to cross the borderline of causality.
The concept of causality is as old as human civilisation. Many philosophies and theologies mention about the causal nature of humans and the universe. The karma siddantam discussed in the Santana Dharma (Indian philosophy) is one such theology. Alright, we shall restrict ourselves to our domain and stick to the topic.
Causal systems are classified as having memory and memory less systems. Causal systems which can respond to causes in the past are all memory having causal systems. This is because, a system can remember causes in the past only if it has memory. Else, they are memory less systems.
What is a Non-Causal System?
A system whose present response depends on future values of the inputs is called as a non-causal system. There are two types of non causal systems namely, acausal and anti-causal.
Acausal systems are those whose present response depends on future values as well as past and present values of the input.
Anti-causal systems are those systems whose present output depends only on the future values of the input or excitation but not on the past and present values.
Whenever we use the term non-causal, it implicitly means acausal in our discussion unless otherwise mentioned.
Now comes the interesting part of the discussion.
Understanding Non-Causality
In the earlier section of causality, we have mentioned that almost all the physical systems that exist are causal in nature. A non-causal system gives an output to the inputs given to the system at some time in the future. It sounds crazy right? It is really hard to imagine any physical system that responds to future inputs. It seems something godly in nature which cannot be perceived easily. This is why non-causal systems usually do not exist physically in nature. They are not natural systems and are considered as virtual in most cases.
When there is no physical system that is non-causal in nature, then why do we classify systems as causal and non-causal when they do not have any physical significance?
Although non-causal systems hardly exist in nature, they can be made possible in virtual environments where we can define our own time axis (not the actual physical time).
Mathematical Possibility of Non-Causal Systems
 |
| Non-Causal system |
Let me define a system mathematically as w(t) = x(t+3). It turns to be a non-causal system. For example, take t=1sec. The system response will be
w(1)=x(1+3)
=> w(1)=x(4)
We can see that the system which we have defined gives the output of 4th second at the 1st second itself. Wonderful! As we have the right to write mathematical equations however we like irrespective of its physical existence, we can also make Non-Causal systems a mathematical reality.
Physical Possibility Of Non-Causal Systems
Alright, we have now understood that non-causal systems can be made possible on paper. But, can we make it really possible in our real world?
The answer is YES! There is a possibility.
Non-causal systems are possible when the system has recorded input and output data.
Let me illustrate it with an example. Let us consider you as a system. Now you are watching a live cricket match. You are now a causal system because your feelings and emotions depend only on what happened in the past and what is happening at present.
However, if you record it and watch the same cricket match later, you will know what will happen after some time in the match (because data of the match is already recorded in your mind). Now, your feelings and emotions concerning the match not only depends on the past and present events in the match but also depends on the future events of the match because you already know what happens. So, if we consider you as a system, the recorded cricket match as an input and your feelings as output and the time axis is fixed with respect to the recorded data as in the above example, then you are a NON-CAUSAL SYSTEM! Hurray!
From the above illustration we can conclude that non-causal systems can be made possible when the system has knowledge of recorded values of input and output values and the time axis is taken in reference to the recorded data.
People and books usually say that all physically realizable systems are causal in nature and non-causal systems do not exist naturally. That is true, this means that no system can be non-causal when it has no data about the future. So, to make a non-causal system possible, we have to provide future data to the system. As it is not really possible to do that naturally, we have to shift the time axis to the recorded data which is advance than the real time axis as we have done in the illustration above.
Final Thoughts about Causality
Causality or non-causality is not just a mathematical representation but has quite deeper physical interpretations. Also, non-causality of a system is possible in some way or the other. That is why it is still present in the literature and we still speak of it.
Friday, October 19, 2012
Substitute Earphones for Microphone in Emergency
2 comments:
Labels:
Computers,
Electronics,
Hacks,
Tips
 |
| Earphone as Microphone |
Most of us these days have microphones (mike) available for our desktop computers and it is usually integrated by default for most laptops. But what if we do not have a mike readily available when it is needed badly? It is true that all of us are hackers intuitively. Whenever we do not have something that we need, we try to make use of other available things to get our work done. We shall do the same here.
Tuesday, July 24, 2012
Automatic Room Light Controller With Single Door Bi-Directional Visitor Counter
66 comments:
Labels:
Electronics,
Home Automation,
Projects
Automatic Room Light Controller with Single Door Bidirectional Visitor Counter is a reliable
circuit that takes over the task of counting number of persons/ visitors in the
room passing through a single door and also turns ON the room light when there
is at-least one person in the room and turns OFF when the room is empty. The
total number of persons inside the room is displayed on seven segment display. We can use any other appliance like fan or anything else instead of the light.
Watch this video to get an overview of this circuit.
Sunday, June 17, 2012
Shadow Counter Circuit
9 comments:
Labels:
Electronics,
Projects
 |
| Block Diagram of Shadow Counter |
Shadow counter is a circuit which can count the number of shadows incident on it. Shadow counting is the main principle of many devices like currency note counting machines, visitor counters, many security systems , etc.
In this article i will teach you how to design a shadow counter circuit.
I have made this circuit based on Shadow Alarm by D.Mohan Kumar published in Electronics For You- January, 2006.
The block diagram of shadow counter is shown above. The intensity of light is sensed by the Light sensor. I have used a Light Dependent Resistor (LDR) as light sensor.
The comparator circuit is designed such a way that its output changes from HIGH to LOW when the shadow occurs. The output of the comparator triggers the monostable multivibrator which in-turn triggers the counter circuit. I have used µA741 Op-Amp as a comparator.
The counter circuit stores the number of shadows occurred in the past and increments the count by 1 unit when triggered. The output of the counter is given to a display using a display driver. I have used a common cathode seven segment display in my circuit.
The monostable multivibrator is used to avoid false triggering. For example, when a shadow is falling for a quite long time (a few seconds), then due to the partial shadows that may occur due to the same object, the comparator gets triggered multiple times for the same object. This increments the count many times for the shadow of only one object. Using a monostable multivibrator in between as I have done eliminates or at-least reduces that problem. I have used a 555 timer as a monostable multivibrator.
You can see the video of Shadow counter here:
The circuit is quite easy to implement. So, I encourage you to do it yourself. This circuit is basically aimed at hobbyists and is also suitable as a college project (mini project) for Electronic Engineering students.
However, I have also done the entire circuit on board along with complete documentation and presentation (PPT) of shadow counter. If you are interested in getting the circuit along with the documentation and presentation, you can contact me by clicking here.
Saturday, May 5, 2012
Combinatorial Digital Circuit Logic Determining Device
19 comments:
Labels:
Electronics,
Projects
 |
| Block Diagram Of Combinatorial Digital Logic Determining Device |
Here is my new electronics circuit for you. This is a brief description/ abstract for the project. Combinatorial digital circuit logic determining device is a circuit which determines the logic of any given combinatorial digital circuit. This is a very helpful tool to know the functionality of an unknown digital circuit. The device has probes which are plugged to the inputs and outputs of the digital circuit under test. This device then determines and displays the functionality of the circuit under test in the form of a boolean equation.
The circuit has number of probes equal to the number of inputs and outputs of the circuit under test. I have implemented it for two inputs and one output. Although, you can make slight modification of the code to make it work for as many inputs and outputs you want.
Wednesday, April 25, 2012
Automatic Water Level Controller With Error Indicator Alarm
10 comments:
Labels:
Electronics,
Projects
 |
| Block Diagram |
Sunday, November 20, 2011
Arduino For Beginners: Introduction and Related Articles
No comments:
Labels:
Electronics
Saturday, October 1, 2011
Simulate Your Digital Circuits With Logisim
No comments:
Labels:
Electronics,
Software
Logisim is a free and open-source tool for designing and simulating your digital logic circuits, featuring a simple-to-learn interface, hierarchical circuits, wire bundles, and a large component library. As a Java application, it can run on many platforms.
Saturday, May 14, 2011
Datasheets Of Frequently Used ICs And Other Electronic Components Download
No comments:
Labels:
Electronics
This collection of datasheets are the most frequently used especially in hobby projects and other academic projects like mini-project, major project for graduation grade students.
Monday, April 11, 2011
Digital Signal Processing by J.S.Chitode - Technical Publications
4 comments:
Labels:
B-Tech,
Books,
Electronics
Monday, April 4, 2011
Microprocessors and Interfacing Textbook by A.P.Godse and D.A.Godse
No comments:
Labels:
B-Tech,
Electronics
Microprocessors and Interfacing- first edition authored by A.P.Godse and D.A.Godse.
Saturday, April 2, 2011
Basics Of Electronics Tutorial
2 comments:
Labels:
Electronics
In this post, I would like to share a set of tutorials covering the basics of electronics in brief using few animations appropriately.
Friday, March 4, 2011
Microsoft Macro Assembler (Masm) x86 with Enhanced Features
13 comments:
Labels:
Electronics
In my earlier posts i have posted MASM software as it is from Microsoft without any significant changes. But, people are finding it a bit difficult to use. So I have made a suit for the original MASM software to make it easy to install and easy to use.
Monday, February 28, 2011
Electronics For You Projects Download
81 comments:
Labels:
Electronics
For your convenience, I have put all the circuits (in PDF) from "Electronics For You (EFY)" into a single bundle for easy downloading. There are about 300 circuits in this package.
Sunday, January 23, 2011
Microsoft Macro Assembler (MASM) x86 Download
3 comments:
Labels:
Computers,
Electronics
Download MASM software Version6 (used in MPI Lab).
Saturday, December 11, 2010
8086 Microprocessor Instruction Set
5 comments:
Labels:
B-Tech,
Computers,
Electronics,
JNTU
This is the Instruction set of Intel- 8086 Microprocessor.
Here, the instructions are classified and grouped into categories to make it easy to understand and to remember.
Subscribe to:
Posts (Atom)
