Author Archives: D.Mohankumar

About D.Mohankumar

D. Mohan Kumar M.Sc., M.Phil, is an Associate Professor from Trivandrum, Kerala, India. He has been guiding Post Graduate students in Animal Science research for the last 25 years in several premier institutions in Kerala, India. He is an avid electronics enthusiast and has been designing circuits for the past 20 years. In this period he has supported many electronics/electrical engineering students in their final year projects. He is a regular contributor to Electronics For You magazine which is South Asia’s largest circulating electronics magazine published from New Delhi. He is also contributing articles in http://www.elprocus.com and http://www.engineersgarage.com/

LCD TV Protector. Design Note 25


SIMAGEometimes you need a simple circuit to protect the Electronic gadgets like LCD TV from voltage fluctuations. Normal domestic power supply is 230 volts at 50Hz in most countries. But this voltage may not remain steady and may go as high as 250 volts or as low as 180 volts. Complaints in the distribution transformer, operation of heavy current appliances like flour mill, welding machine etc in the nearby places can cause severe voltage fluctuations in the lines. A good stabilizer with Buck / Boost facility can solve the problem, but still it is interesting to make this circuit and it costs less than Rs.100.It cut off the power supply to the gadget connected when the voltage increases above 230 volts and decreases below 200 volts.
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Understanding Symbols. Design Note 24


COMPONENTSAn Electronics Hobbyist needs to know the symbols of the electronic components in the Circuit diagram. Before starting the construction of a circuit, it is necessary to study the circuit diagram first. It has a number of symbols with the values marked. There are different symbols for representing the components. So it is necessary to study the symbols generally appearing in circuits.
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Understanding Capacitors. Design Note 23


TANTALUM As you know, Capacitors are inevitable parts of an electronic circuit, without which the circuit design is incomplete. Different types of capacitors are used in electronic circuits; each performs a function in the circuit. But basically, all the capacitors act as energy storing and transferring devices. Let us discuss the capacitor types, identification methods and functions.
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Audio Amplifier. Design Note 22


TDA2002As a Hobbyist, you need simple amplifier circuits to make audio projects. Here explains the design of two Simple Amplifier circuits using IC BEL 1895 and TDA 2002.
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SCR Latching Circuit. Design Note 21


SCR Silicon Controlled Rectifier ( SCR) is a semiconductor device used in switching applications. Unlike Transistors, SCR latches once triggered and remain on even if the triggering voltage at the gate is removed. The device can be switched off by removing the Anode current through a Push- to- off switch or by disconnecting the power supply.
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Make a Joule Thief. Design Note 20


Joul-Thief-CircuitJoule thief circuit is a self oscillating voltage booster circuit that gives high volt from low volt, say 3 volt from 1.5 volt. So by exploiting this property, we can light a 3 volt LED using 1.5 volt pen cell or charge a mobile phone from 3 volt solar cell or two 3 volt pen cells. It is called as “Joule thief” because it is stealing energy or joules from the battery. Let us design the Joule thief circuit.

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Infrared Alarm System. Design Note. 19


IR-LED-PairThis design note explains how to design an invisible alarm system easily. Infrared Transmitter ( Tx) and Receiver ( Rx) LED pair is easily available which can be used for making this alarm system. Infrared transmitter LED emits infrared rays in the wavelength around 950 nm. This LED is a high current device that can handle more than 100 mA current. The IR receiver LED is a kind of Photodiode that generates a Photo current when it receives IR rays. So the IR LED pair is ideal to make an alarm system that operates both day and night.
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