How Mosquito Racket Works......%....

Hello everyone!! In this section we’ll be seeing different circuits and their applications. Has anyone seen this ?

No it’s not a tennis racket! It’s a mosquito racket. This is what happens in it: it has got an inner grid and an outer grid. These two terminals are from a voltage doubler – where the voltage has been doubled and tripled to such a level that the voltage is in thousands of volts. Now along comes an unassuming mosquito which gets caught in between the terminals. The circuit is completed and a very large voltage is applied to the mosquito which causes it to explode.

To see a quick demo of what we mean click here

There is rechargeable battery in it which stores DC charge when the. This DC is converted to an ACsignal using an inverter and that is given to a voltage multiplier which produces a high voltage. This very high voltage is given to the two terminals of the grids.

As the name suggests this circuit converts AC electrical power from a lower voltage to a higher DC voltage, typically using a network of capacitors and diodes. In principle it’s a rectifier. We can see that from the presence of the diodes.

The input is a sinusoidal AC signal. During the positive half-cycle, diode D0 conducts, D1 is cut off. The capacitor C0 will charge to the peak rectified voltage. During negative half-cycle, the diode D0 is cut off and D1 will be forward biased. Diode D1 is a short and D0 is open. So take it as a loop as shown below.

So at the point marked A the voltage will be the sum of the negative peak (Vm)and the voltage across the capacitor with the sign as shown. This is 2 times Vm Similarly C2 will be charged to 2Vm in negative half-cycle. Since diode D1 is short then, the voltage at A will charge the capacitor C1. The voltages will be as shown:

Vmeter1 will read 2Vm and Vmeter0 will read Vm plus 2Vm which is 3Vm. Thus this can be repeated with consecutive stages. Voltages taken at the top of transformer winding as shown will give odd multiple voltages and voltages taken from the bottom transformer winding will give even voltage multiples. Confused? Okay. Add another stage i.e. capacitor and diode,then think what should happen.

Friends’,analyzing a circuit is not very tough. First know what the inputs are – in thiscase a simple sinusoidal ac signal. That is half the job done. Then see how the behavior is for that particular input. If you can break down the input into further steps it’s much better. Understanding the behavior of the various components will help you further follow up the working. Well I guess it may allsound a bit weird, but we’ll be seeing more of this in the coming weeks with more interesting circuits and electronics fun. Meanwhile why don’t you tryrigging up this circuit and running it?  The capacitors are 1 nF. And an input more than 2V is better as the diode has to be forward-biased.

Let’s look at some places where this circuit is used. Voltage doublers are used in switched mode power supplies. Some power supplies require 120 V as well as 240V. So an SPDT switch will be used to select either of the voltages. Voltage tripplers are used to create high voltages in CRTs, printers and photocopiers. Note that even though very high voltage is to be generated, the individual components need not withstand the entire voltage range.

7 segment display

We have been working a lot here. And have come up with some more cool components. 

7 segment display

 It’s a simple counter display that displays the values counted from 0 to 9. This has many interesting applications. One such application is as a token display in banks and hospitals which will display which token is present at the counter and a simple push of a button the next number is displayed.

For this circuit a 7447 IC is essential. This IC is a decoder which converts the BCD input to its corresponding seven-segment code. This code is used to light up the corresponding LEDs in the display so that the BCD number is displayed in decimal. The input of the decoder is given by a simple MOD 10 counter (in real life such ICs like 7490 are used for BCD counting and yes, we’ll be adding it soon too).

It’s that simple. The counter counts from 0 to 9 and the corresponding number is displayed.

Understanding Multiplexing on Wireline Telephone Systems

Communication is a vital part of our lives. From Marconi’s first transatlantic transmission to the advent of satellite communication, intercontinental cables and optical fiber communication it has overridden our lives. Communication is either digital or analog and uses many techniques.

The most essential resource in communication is the channel via which communication takes place. Take a telephone network. The channel – let us assume wired connections – will be at a scarcity, that is, for a single channel there will be many users vying for it. In digital communication the analog data will be converted to digital bits and that should be transmitted. Let’s take an example for a 24-channel system, having a sampling rate of 8000 samples per second, 8 bits per sample, and a pulse width of approximately 0.625 µs. This means that the sampling interval is 1/8000 = 0.000125 s = 125 µs, and the period required for each pulse group is 8 x 0.625 = 5 µs. For each of the 8000 samples, 5 µs would be taken up by the pulse group (series of bits) and the remaining 120 µs would be made up of nothing. Thus to make use of the channel efficiently time division multiplexing is used.

What is time division multiplexing? It is a system where different groups of bits from different transmitters are sequenced one after the other in time and transmitted. Similarly the correct receiver is synchronized such that it receives the correct data. So in the above example then in one sample of 125 µs, 24 different bit samples can be transmitted each of 5 µs duration and the 25th bit sample for synchronization. To say in simpler terms, say 3 people want to use the same channel to communicate with 3 other people. They can share the channel on a time-shared basis. So the first two people will be talking till a certain time T1 and then till time T2 the next pair will use the channel for communication and so on.

Look at the circuit. It consists of a multiplexer (MUX) at the transmitting side and a demultiplexer (DEMUX) at the receiving side. A multiplexer is a switch which routes the input to one of its many outputs which is chosen depending on the binary number at its ‘select’ lines. The DEMUX works in the reverse manner to the MUX. Note that to show the synchronization the same pulse train has been given to the select lines – at the transmitter and receiver. In real life a sync bit will be sent along with the data bits which will instruct the multiplexer as to which receiver the particular data stream is to be transmitted. In synchronous multiplexing, the order of shifting of inputs in the common channel is also synchronized with that of the channels in the demultiplexer. Say as in the example, 5 µs for the bit stream means that the timing at the DEMUX such that the outputs will be shifted after every 5 µs.

For input you can give the bit stream of your choice and see whether the data from first input is received at the corresponding output and so on. The bit period in the circuit we are discussing is 1 ns. So for each nanosecond the communication shifts between channels and thus 8 lines are virtually active in the single channel. Since the time range we are speaking in is in microseconds and nanoseconds the shifting will be very fast and all the 8 lines that are in communication will not be aware of the change.

Note: The communication although digital will be modulated as PCM (Pulse Code Modulation) as there is no way a bit can be directly sent. The PCM waves will be sent via cable after modulation – done after multiplexing – and at the receiver it is demodulated back and demultiplexed in to the various channels, and at each channel the digital data is converted back to analog (like voice, for example) for the receiver.

Radio : How it's work !!!!!!

You must have seen the radio that your grandfather loved listening to as you grew up.  I bet you loved turning the tuner knobs either way when no one was around!

You always wanted to know what the letters “AM” and “FM” meant. Today lets try to decode one of them. But before that, lets try and understand – What is modulation? Modulation is the process of changing a characteristic of a carrier wave with respect to a modulating wave. This modulating wave is otherwise known as the message signal which has the information to be transmitted. For example in amplitude modulation (AM), the amplitude of the carrier signal is varied in accordance with the modulating signal.

Amplitude modulation, more popularly known in its abbreviated form as “AM”, is a method of communication used mostly in the form of radio waves.  Amplitude modulation was originally engineered for use with the electric telephone (modern-day telephone) to add audio to a receiver connected to a telephone transmitter. In 1906 conducted an audio exhibition using amplitude modulation to broadcast audio signals using radio waves. From the exhibition in 1906 to modern day radio broadcasting, AM is still being used, referred to as the “AM Band”.

Another way is FM (Frequency Modulation). While FM offers greater clarity for audio, and the higher frequencies that FM use offer a wider bandwidth, allowing for more information to be transmitted, one application where FM and digital are not suitable are Aviation communication, which to this day still use AM analogue. This is because weaker signals can be heard over stronger, closer ones with AM, allowing for emergency transmissions to have more chance of being heard over other traffic. Also, AM uses a narrower bandwidth than FM, allowing more users in a smaller space. This is important for the lower frequencies of Radio, where space is at a premium.

The next question is why do we have to modulate any signal? The alternative to modulating a wave and transmitting it is to send the wave as it is un-modulated. The first obstacle in doing that is the receiving the information. For efficient radiation and reception the transmitting and receiving antennas would have to have lengths comparable to a quarter-wavelength of the frequency used. In other words the shorter the wavelength (higher the frequency) the shorter the antenna need be. As a result of modulation, the low frequency message signal is ‘carried’ by a wave with a higher frequency.

The transmitted messages in AM radio are mainly music and voice in the audible range of 20 – 20 kHz. Due to this all the signals from all the AM stations will be mixed up in a very small band of frequencies. It would be difficult to separate the required message signals at the receiver unless they are converted to different frequencies of the electromagnetic spectrum. At the receiver a tuned circuit will be present to extract the required frequency for demodulation.

Let us see a circuit in which the given carrier is modulated depending on the modulating signal.

The BJT must be biased properly to get a correct output. The carrier is connected to the base and this is amplified by the BJT and flows in the collector, but again the current is restricted by the opposing flow from the modulating wave connected to the emitter. As a result the output amplitude is varied according to the opposing modulating voltage.

One thing should be maintained in the AM circuit. That is that the message signal voltage (Vm) should be less than the carrier voltage (Vc). This relationship is known as the modulation index (Vm/Vc) and it should be between 0 and 1. When it is more than 1, or if the Vm is more than Vc, then distortion occurs. Let’s see the output of the above circuit – the modulated wave. 

Verify the frequency of the signal to be equal to the carrier frequency. Also note that the envelope of the modulating wave varies with reference to the carrier wave. So the amplitude of the modulating wave should be less than the carrier signal amplitude else the wave distorts. If the wave is distorted then a portion of the trough in the modulating wave will be clipped. As a result information is lost. You can see it practically by varying the amplitudes in our simulation and see the effects.

The expression for the modulation index is given as m= Vm/Vc = (Vmax – Vmin)/(Vmax + Vmin). Vm = (Vmax – Vmin)/2 and Vc = (Vmax + Vmin)/2. Refer the diagram given below.

The frequency spectrum would give the frequency components in the AM modulated wave. The frequency spectrum cannot be plotted like the frequency response. But you can reads more information about it from here:

Some useful video links are this and this.

The Main Difference between Active and Passive Components --> (Very Easy Explanation with Examples)

The Main Difference between Active and Passive Components

Active and Passive Commonest (Very Easy Explanation with Examples)

Active Components:
Those devices or components which required external source to their operation is called Active Components. 
For Example: Diode, Transistors, SCR etc…

Explanation and Example: As we know that Diode is an Active Components. So it is required an External Source to its operation. 
Because,  If we connect a Diode in a Circuit and then connect this circuit to the Supply voltage., then Diode will not conduct the current Until the supply voltage reach to 0.3(In case of Germanium) or 0.7V(In case of Silicon).

--------------------------------------------------------------------------------------------------------------------------------- 

Passive Components:

Those devices or components which do not required external source to their operation is called Passive Components. 
For Example: Resistor, Capacitor, Inductor etc…

Explanation and Example: Passive Components do not require external source to their operation. 
Like a Diode, Resistor does not require 0.3 0r 0.7 V. I.e., when we connect a resistor to the supply voltage, it starts work automatically without using a specific voltage. If you understood the above statement about active Components, then you will easily get this example.

In other words:

Active Components:
Those devices or components which produce energy in the form of Voltage or Current are called as Active Components
For Example: Diodes Transistors SCR etc…

Passive Components:
Those devices or components which store or maintain Energy in the form of Voltage or Current are known as Passive Components
For Example:  Resistor, Capacitor, Inductor etc…

In very Simple words;
Active Components: Energy Donor
Passive Components: Energy Acceptor
Also Passive Components are in linear and Active Components are in non linear category.

Paperduino: How to Print a Paper Arduino

New and easy way to print PCB



Paperduino: How to Print a Paper Arduino