Circuit Design

 The FM demodulator is done with the help of a circuit called Phase Locked Loop (PLL). A PLL should have basic functional blocks like Voltage Controlled Oscillator (VCO), Phase comparator, Low Pass Filter (LPF) and Source follower. In the demodulator circuit the VCO generates a frequency which matches the original carrier frequency and compares the phase of that with received FM wave using the Phase comparator. The output of the Phase comparator is filtered out using the LPF and is current amplified using a Source follower.The output of the source follower matches the original message signal. To implement all the above mentioned circuitry is a difficult task, but there are ICs available which has all these circuit blocks embedded in it. In this article the FM demodulation is done with the help of a PLL IC called HEF4046. 

This tutorial explains circuit designing using a 555timer to generate a frequency modulated wave. Along with 555 IC timers, the circuit is designed around a Wien Bridge Oscillator circuit and a clamping circuit. Out of many methods of frequency generation, this tutorial covers one of the simplest and most efficient circuits. From its generation to modulation, the wave suffers minimal distortion and hence, a near accurate output is generated. The circuit can be easily assembled on a breadboard and connectors can be clamped anywhere to get an output on CRO. The process is divided into three states, namely, sine wave generation; positive wave clamping; and wave modulation. The wave is generated using Wien Bridge oscillator, is clamped and then is modulated by 555 based timer circuit. There are several curious questions to this design, such as in what mode is the 555 timer made to work? How the Wien Bridge Oscillator circuit is designed?  Continue reading to reveal these answers and other interesting information about this circuit. 

The amplitude modulation is the simplest modulation technique among the wide verity of modulation techniques in use. In this technique the amplitude of a high frequency signal is varied corresponding to the variation in the amplitude of the low frequency modulating signal. The demodulation of an AM wave can be done with only few components and unlike most of the demodulation technique there is no synchronization required between the modulator and demodulator circuits. The message signal appears as an envelope over the amplitude of the carrier wave and the demodulator make use of this to extract the modulating signal from the carrier and hence the technique of AM modulation is called envelope detection.This article demonstrates how to generate an Amplitude Modulation (AM) and demodulate the same wave to get the original modulating wave. The AM wave is generated based on the circuits explained in article on AM modulation. 

The AM modulation is a kind of modulation technique which is in use since the very early days of wireless data transmission.  In a radio transmission system there is a relation between the ranges of frequencies which can be transmitted wirelessly with the length of the transmitting antenna. The relation is inversely proportional to one another, means as the frequency of the signal to be transmitted increases the length of the antenna can be reduced and as the frequency of the signal to be transmitted decreases the length of the transmitting antenna should be increased accordingly.Using an antenna of few meters the frequencies in the range of Mhz can be easily transmitted to a distance. The basic purpose of the wireless transmitting system in early days was to transmit the audio signals, but to transmit audio signals which fall in the range of few Khz an antenna of more than a kilometer height would have been required.  

Step: 5) Design circuit for each functional block In this step we will be designing the circuit for individual blocks. The circuits required are simple and very basic circuit known to all; hence it won’t be such a big task. We are not designing anything new, but modifying the well-known basic circuits to suit our…

Step: 8) Find reusable modules from the circuit diagram   Whenever we do hardware designing, the first rule is to make it in modules that can be reusable. The modules that we make for this particular project may come useful in another project and hence reduce the development time for that project. Even if a…

Step: 10) Assemble the modules and test the assembled unit We have built the reusable modules and we have a good idea from the circuit diagram about how their pins should be connected together. At this point we don’t have to worry about the internal circuits of the module and all we need to take…

The switch ‘SW’ is connected for testing in such a way that it can close and open the contact with the ground and PIN C of the BOARD_A. The PIN B should be connected with the PIN D so that the INDICATOR module can get positive voltage. Suppose when the power is applied and the…