Components are still available

One of my readers is always concerned about the availability of some components used in my circuits. Even though new makes are releasing continuously, the old makes are still in the market. Indian electronics market is rich in new as well as old components and the old one cannot be considered as obsolete. Substitutes are also easily available. We cannot argue if the component is not available in one country since the availability and use varies in different regions. A wise designer can easily substitute a component if the make shown in the circuit is not available.

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Electronics circuit design is an intelligent act which requires theory as well as experimentation. Too much theory will always confuse because theoretical calculations and actual working of the circuit varies since most of the components are not 100% accurate in working. So experimentation is better than over dependence on the calculator. For example if we select 1K current dropping resistor through ohms law calculation, in practical use it will be 900 ohms or 1100 ohms. Theoretically there will be 0.7 volt drop in the base emitter junction of a transistor and 1.8 volt drop across the LED. Practically it can vary. For example if you measure the forward voltage of 10 LEDs purchased from the same pack, the forward voltage of the LEDs may vary from 1.5 volts to 2 volts. This is the real situation. Similarly, a leaky capacitor will not charge completely. This will upset the total calculation. Without blaming the design, the wise decision is to change the component or replacing the value. A person always stick on too much theory cannot do this but an experimenter can solve the problem within seconds. Experience and practical knowledge can do lot of helps in this matter. That is the intelligence in circuit construction. I am not depending on too much theory but considering only the average values of resistors and capacitors since + or – 1 % change will not affect the performance of the circuit if it is not a sensitive one. Only after constructing the prototype, it is possible to see the difference in the theoretical calculations and the working of the circuit. Following are the images of the so called obsolete components which are still available in most places.

2N2222 Transistor

2N 3055 High power transistor

Zener diodes are now available down to 1.2 volt rating

100 Ohms to 10K Thermister is easily available

This 7 Segment display requires only 3 volt and 10 mA current

AC 187 transistor is still in the market.It is also coded as Bel 187

BS 170 Mosfet

BT 169 SCR performs well

SK/CK 100 PNP transistor is still existing.It is also coded as BEL 100

IC 7555 is the low volt CMOS version of IC 555 widely used in circuits. It works down to 3 volts

This buzzer works in 3 volts

Unlike common high watt LED, this LED requires only 40 mA current

This is the new version LED that requires only 1 volt.It will burn out in 2 volts. It requires only 10 mA current

SL 100. This medium power NPN transistor is still in shops.It is also coded as CL 100 or BEL 100

UM 3481. Multi tone ROM IC is available in most places. Ideal for Door bell

UM 3561 Siren generator works in 3 volt lithium cell


2 thoughts on “Components are still available

  1. D.Mohankumar 8 Mar 2012 / 6:19 pm

    Hello Vhhp
    Thanks for your great encouragement. In this digital world, the concept of virtual class room and virtual learning is increasing. Any body can share the knowledge through net so that the needy persons can utilize the information.Now a days, students learn more from various sources than the contact learning from the class room.I have more than 200 students all over the world and I am spending more than 3 hours per day to clear theirs doubts.I think, spreading the knowledge is better than keeping it in the mind.

  2. vhhp 8 Mar 2012 / 7:36 am

    Dear all,
    Every one should remember that they are different from others and so as the areas they live in. Change in life style changes the market. I am greatful to Sri. D. Mohan Kumar for his service in educating the students of biology, electricity and electronics. I do not know about foreign countries, but India needs people like this GURU. I know how difficult it is to find an instructor of electronics in India. My sincere regards to this master.
    ..V. Hari Hara Prasad
    25-666-1-a Vasantapet, Proddatur- Kadapa District- A.P. India Pin: 516360

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