Power on reset

Power on reset is an essential requirement for sequential circuit based modules. We consider a simple example, consider a remote controlled tube light or fan system, the circuit of interest is shown in below image.

The IR Rx is a infrared Receiver which trigger the DFF and switch ON/OFF the fan depending previous state of the DFF. The circuit is practically laid down on the PCB and is working fine. However, when the power is turned on some time the fan ON and some time OFF. It has happened that when supply  line is goes off, and supply arrive later the fan can turn on automatically. The problem is the DFF can attain logic high or low state and was unpredictable. 

In order to solve the problem, we need power on reset. Here R and C in the circuit do the job.

Whenever power is turned ON, while charging the capacitor, there is a current passing through the resistor and hence voltage across the resistor. This voltage uphold the reset pin of the DFF. The by selecting proper R and C values we can meet the reset condition of the DFF.After charging the capacitor C completely, reset pin is  grounded as there is no current through resistor. 

Very simple!

Communication within 10cm!

Who will not laugh at me if I say "There is a system which communicate in the range less than 10cm..!" Do we need a system or device to communicate within 10cm? what a stupid idea...!?

Sorry, I am confident and don't mistaken me. I am talking about the communication within 10cm only. Oh...that is new wireless communication called NFC. 

Before talking about NFC, I will give an example. You go to a  city and looking for roadside candy for Rs.7. You have 500/-  and no change. You have to roam here and there to have change for 500/- or candywala needs to give change for you. I have experienced that both the ways are difficult.

You believe me, you have one more choice now.  "Just hold your mobile very near to candywala's mobile..and take candy in your hand..that's all".

Yes, that is possible in few years. The new wireless communication system called Near field communication(NFC) is developed for mobile and alike devices for secure transactions, business card exchange and may be for identity as well.

The NFC is not made for file sharing and huge data transfer protocol like wifi or bluetooth. Since the range is less than 10cm, inherently secure than other wireless technology. 

NFC is a extension of RFID. An RFID system operate in wide range of frequencies. However, an NFC system is standardized to 13.56MHz.Since many frequency bands are already allocated to different functions in different countries by FCC, only 13.56MHz is freely available band.It is also noted that this band of frequency is also good enough to meet VLSI design standards(lower the frequencies bulkier is the systems and higher the frequencies power will be high).

Recently released android mobile Nexus -S has NFC. The NFC usage is not yet grown enough to build trust in the society.Tech news sites have reported that 6 out 10 multimedia sets will have NFC by 2015. 

I will happily welcome you NFC..! 

Trainer is not a 'train' but a Teacher

"Teaching is the best way to learn". I too believe this statement. If we read the books,paper or INTERNET pages any subject is felt like so simple!!!. I believe that knowledge of a person is valuable if he practically makes a material out of it and able to transfer the same to the next people. In order to maintain richness of knowledge base industry every one needs to be trainer and trainee. I am good trainee and wanted to be a good trainer....i.e, BOTH.

I was to much enthusiast to become a trainer and I did many kind of testings at the beginning itself. The test cases which I did and aftermath of them are listed below:

1. I wanted every one to be on time to classes(punctuality).
2. The trainees need to be happy and comfortable.
3. The technical matter should be discussed in way that enthrall the class, however, the technicality of any concept should not be wrongly taught.
4. Do mistakes, but agree to mistakes rather than some one forces us to agree.
5. In technical discussions, no matter who/what/where/when talks, if something is wrong raise the doubt and question it for clarifications.
6. Have a good friendship with trainees.
7. Explain the subject with examples where everyone can understand the things well.
8. Be a free teacher, who is available all the time-in messages, chats, emails, class or lunch or dinner table.
   
9. If the class is not going in the directions as expected, entertain the trainees by asking their hobbies and presenting them(like singing..jokes...shayirees...)Come back to technical with relaxed mind.
10. Not to be strict on assignments, but convince the trainees about their responsibility.

However, I failed in some of the things-

• Some time, we need to stop questioning the people even if they are doing wrong as their ego may hurt and it may start bleeding.
• Very critical-never have friendship with trainees. We can not teach friends,but be friendly.
• Not to be available freely. There is no respect for things which comes free..!
• Technical classes, needs to be completely technical(for point-9), I did not understand, why people separate technical stuff from other stuffs?
• Assignment-we needs to be strict.

Any way, every day is a new learning assignment and I use past history for betterment of self and surroundings. I am confident for training once again with modifying wrongs things of past training.

I would like to take an opportunity here to thanks all the trainees, who have enjoyed my training and those who suffered because of my tests.

Noise about "NOISE" in circuits

Hello, who never heard of noise in integrated circuits(IC)..!...white noise,Gaussian noise, flicker noise, 1/f noise and so many different terminologies. I can talk about NOISE and make some noise and I agree that I don't know exactly about what are these dirty noise in my systems is. However, there are noise in systems which are internal to the system and some which are influenced by the external world like-another circuit besides it, environmental radiations etc.

I have a confusion -whether noise is positive or negative with respect to ground?

We operate circuits with positive supply(with respect to ground).NB:ground is decided by the battery and not by circuit). However, it is important to have proper ground and supply connection to a circuit.

If we operate a circuit (say CMOS inverter) with following topology(shown in image right side one),do we get any advantage over the noise performance?

No doubt, the input of for the new topology also be need to change with respect new reference.However, are we achieving any thing good here. It is one of  the thought in opposite to classical definition of reference and ground.

Let me know your views. Comment please.

Ubuntu:What is special about it?

Every engineer, whatever his/her branch of studies, will aware of computers.When there is a computer, there will be  windows OS. But now the situation is changing. People are moving towards free software/open source softwares. Ubuntu is one of such free OS and almost graphically look like windows.I can say good competitor for windows.  

All people are biased with windows and say linux is not user friendly. I believe that Ubuntu is exceptional with respect to user friendliness and with engineers view- it  is far.. far.. better than windows. 

What are the advantages of ubunut?

1. No virus(Every OS can be hacked, but it very less chance for linux OS systems).
2. Completely free.In 2010, Ubuntu has freely provided the OS cds. Now any one can download from here.(10.04 is good one. recently 11.04 stable version released).
3. One time installation; you will get all softwares-No separate installation for drivers, adobe reader,open office,audio players, video players, games,.....never ending list. If you need any software jut search in "Ubuntu Software Center".
4. Engineers have very good deals with Ubuntu. We can change the systems the way we wanted it to be.All kind of languages-Perl, C ...etc are inherently inbuilt. Also for circuit enthusiasts-PCB design, VLSI design, SPICE simulation tools are also available.
5. Recently computers are coming with higher memory hard disk and RAMs and hence no trouble with speed or OS size.

Demerits:

1. We all have background of windows and we refrain ourselves from looking an OS other than windows angle.
2. Installations of software is little bit tricky in linux- No simple click !
3. I suggest the beginners to talk about basics of linux with anybody who knows about linux.
4. For property devices - for mobile, ipod, mp3 players no drivers available in linux. This is the only one worry that will make us to keep a copy of windows in our systems.

Some facts about Ubuntu:

1. Brazil is completely linux-ised.
2. Kerala government school supports linux(Read here)
3. 100% on line supporting community.
4. Live CD boot-able options.
5. If your windows got "viral infection and died", then Ubuntu live CD is only way (As I know)to recover your data.

I welcome you all for Ubuntu OS.Ubuntu is made for human beings..!