When we speak of electronics,our talk could span a wide area.Starting from the most primitive vacuum tubes(transistor tubes) or even back to the conduction or motion of electrons and could possibly end with the most sophisticating circuits which are now embedded in a single chip or a bunch of them again embedded inside another one.But it will be always supportive to stick to the more basic concepts, which helped us to build the most demanding ones as we see today. From my observations, I realized that so many people who begin to think about electronics, will somehow start their hobby projects with integrated circuits or more commonly nowadays , with assembled modules like arduino board, Bluetooth modules,RF modules etc...
Due to this tendency , they are lacking the true FUN and THRILL of electronics.So here, I will try to convey my ideas which would help the readers to encourage themselves to look at electronics in a more wide perspective.
We would speak about the two LEGENDARY and REVOLUTIONARY basic components of electronics :
THE RESISTORS and THE TRANSISTORS.These descriptions are not purely based on formulas or theories which we usually do in our classes on paper,instead we will try to link those with some tricky facts in practical approach,which I believe ,will surely amaze our friends.
Lets start to explore the fun essence of electronics........
Step 1: The RESISTORS
Resistor is one of the famous components among the hobby guys.Everybody would be familiar with resistors.As it is clear from its name itself,resistors are those components which will resist the current flow through them.As it resist the current flow and also its resistance value being constant , the voltage across the will be provided by the equation V=IR which is our marvelous ohm's law.All these are well clear concepts.
Now time for some tricky analysis....just for fun
We have a 9 volt radio battery and a 3 ohm resistor.When we connect this resistor across the battery as shown in the figure , surely we get a current flow as depicted.what amount of current will flow?
Yes , no doubts , from our own ohm's law the answer will be I=V/R=9/3=3 ampere.
What????3 ampere current from a radio battery at 9 volt????No,its not possible.
In reality, the battery is only capable of providing a small amount of current at 9 volt.Say it will give a 100 milli amps of current at 9 volt.From ohms law the resistor must be of 90 ohms at least to balance the flow.Any resistance below it would reduce the voltage across the battery and increase the current so as to balance the ohms law.So when we connect a 3 ohm resistor , the voltage across the battery would drop down to V=0.1*3=0.3 volt(where 0.1 is the 100 milli amps i.e.,the max current of the battery).So ,literally we are short circuiting the battery which will completely discharge it soon and make it useless.
So , we must think beyond mere equations.COMMON-SENSE WORKS!!!
Step 2: Resistors for Shunt Measurements
Resistors can be used to measure the amount of current flowing through a load, if we have no ammeter.
consider a circuit as shown above.The load is connected to a 9 volt battery.If the load is a low power device , lets assume the current flowing through it to be 100 milli ampere(or 0.1 ampere).Now to know the exact amount of current flowing through it we could use a resistor.As shown in the figure , when a 1 ohm resistor is connected in series to the load ,the by measuring the voltage drop across the 1 ohm resistor we could get the exact value of the current from ohms law.That is the current will be I=V/R,here R=1 ohm.So I=V.Thus , the voltage across the resistor will provide the current flowing through the circuit.One thing to be remembered is that , when we connect the resistor in series , there is a voltage drop across the resistor.The value of the resistor is so determined that the drop is not so high to affect the normal operation of the load. That's why we must have a vague idea of range of current which would be drawn by the load,which we can acquire though practice and common sense.
Also we could use this series resistor as a fuse.That is, if a 1 ohm resistor is of power rating 1 watt ,then it means that the maximum amount of current which could flow through it will be 1 ampere(from the equation of power(W) W=I*I*R).Thus if the load is of 1 ampere maximum current capacity this resistor will act as a fuse and if any current more than 1 ampere enters the circuit the resistor will blow up and become an open circuit , thus protecting the load from over current damages.
Step 3: The TRANSISTORS
Transistors are super heroes in electronics.I love transistors very much.They are the main revolutionary component which revolutionized the entire electronics field.Every electronics lover must achieve a strong friendship with the transistors.They are capable of making a very long list of variety electronic functions.
To start with ,every one would be familiar with the definition that ''Transistor means transfer resistance".This is the amazing capability of transistors.They can transfer the resistance in the output section(commonly collector-emitter line)when we change the current in the input section(commonly base-emitter line).
Basically there are two types of transistors : npn transistors and pnp transistors as shown in the figure.
These transistors associated with various valued resistors will form numerous logic circuits , which even form the firm back bone of our modern days processor chip's interior designing.
Step 4: Npn Transistors
It is generally taught roughly that , npn transistor get ON by giving a positive potential(voltage) at the base.Yes, it's true.But in a more wide perspective we could describe it as follows .
When we make the base of the transistor at a 0.7 volt higher potential(voltage) with respect to the emitter of the transistor ,then the transistor will be in the ON state and current flow through collector-emitter path to ground.
The above point helps me a lot to solve almost all the commonly found transistor logic circuits.This is depicted in the above figure.The polarity and the current flow path will ensure much more friendliness to our transistor.
When we provide this 0.7 volt high at the base, this results in a flow of current from base to emitter and is called the base current(Ib).This current multiplied with the current gain will provide the collector current flowing.
The working is as follows:
When we first set a 0.7 at base then the transistor is ON and current begins to flow through the load.If some how the voltage across the base and emitter is increased the to compensate that the transistor will make less base current to flow thus keeping the voltage at 0.7 itself,but in contrast the collector current also decreases and the current flowing through the load decreases ,in effect the voltage across the load also decreases.This shows that when the voltage at the base is increased the voltage across the load would decease and thus this reveals the inverting nature of transistor switching.
Similarly if the voltage decreases(but above 0.7) then the current would increase at base and thus in turn increase at the collector and through the load thus increasing the voltage across the load.Thus a decreasing in the base will lead to increased voltage at the output,which also reveals the inverting nature on transistor switching.
In short the striving of the base to keep its 0.7 voltage difference is utilized by us in under the name Amplification.
Step 5: Pnp Transistor
Like npn transistor ,the pnp transistor is also commonly said that ,by giving a negative to the base the transistor will be ON.
In another way, when we make the base voltage 0.7 volt below or lesser than the emitter voltage ,then current flows through the emitter collector line and load is fed with current.This is illustrated in the figure.
The pnp transistor is used to switch positive voltage to the load and npn transistors are used to switch ground to the load.
As in the case of npn ,when we increase the difference between emitter and base, the base junction will strive to keep up the 0.7 volt difference by changing the amount of current through it.
Thus by adjusting the amount of current through it in accordance with the variation in voltage the transistor could regulate the balance between input and output ,which makes them very special in applications.
Step 6: Conclusion
All the above ideas are very basic and are known to many of my friends.But I believe that it would be helpful for at-least one person in the field of electronics.I am always attracted to these kind of very basic ideas ,which help me to solve and reverse engineer a number of circuits,through which i believe we could gain a lot of experience and fun.
I wish all my friends good wishes.Thank you.