Thursday, June 14, 2012

Stuff that dreams are made of

Look up biographies of any of the famous scientists or engineers and you will invariably have come across a common theme: their dads made sure that had access to an encyclopedia. Having interacted with many accomplished academicians, scientists and engineers myself, I find this to be the trend even to this modern day: if the environment is conducive, people carry their dreams from childhood to adulthood and try their best to realize it.

The dream imparts meaning to their lives, fuels them ahead and gives them something to believe it. And it is essential that you acquire this dream as early as possible in your life.

I became an electronics engineer because I wanted to. I am not yet an expert and only time will tell how good I become at my job. But I love the feeling that you get when you get to do the things that you always wanted to do.

I realized that one of the ways I can help kids achieve the same feeling later on in their lives is to help them acquire a dream. A dream in which they see themselves as becoming someone particular - taking up a particular role in the human society and excelling at it.

Its easy for kids whose family are well off, to gain access to such materials. But it is even more important for the lesser privileged ones to gain access to these materials and have and inspiring dream strong enough to steer them away from the evils of the society.

So I decided to buy lots and lots of encyclopedias and give it to my friend Anushri who has been a Tech for India fellow for over an year now.

We raided Landmark @ Infinity mall, versova and picked up encyclopedias on all kinds of topics - general science, technology, biology, wildlife and most importantly astronomy (every kid would want to be an astronaut!). We made sure that all of these had lots of photos and illustrations - it wouldn't matter if the kids haven't learnt to read yet, they can always look at the photos and be excited. Dorling Kindersley is one of the best publisher when it comes to illustrated encyclopedias (wiki | India | Catalog/UK Shop)

Return to innocence - we couldn't help but be mesmerized by the glossy illustrations ourselves

A suitcase full of encyclopedias.
(surprisingly inexpensive, the whole thing cost only 5800 INR)

Anushri with some of the books
Anushri maintains an awesome blog here. Looking forward to reading her posts in the coming months on how this experiment goes. I hope it achieves the desired results - for that we will have to wait for 20 years as the kids she is working with are currently in 2nd and 4th grade. 

I also gave her my old digital camera which she can give to her students turn by turn for 'show and tell' assignments - they take the camera home, shoot pictures of anything they like and come back the next day and tell a story about it as they flip through the photos on the digital projector.

Richard Feynman - one of the most awesome scientists of modern times - too had a set of Encyclopedia Britannica when he was a kid. In the following video he relates to how his father was instrumental in inculcating scientific curiosity in him.

Thursday, June 7, 2012

Why is the transistor BC547 so-named?

BC547 is a general purpose NPN Transistor (datasheet here) which us very popular among hobbyist and engineers alike. But why is it so named?

The naming or more specifically “numbering” of most transistors can follow any of the three systems:
1. Pro-Electron (European)
2. Joint Electron Device Engineering Council (JEDEC)
3. Japanese Industrial Standard (JIS)

BC547 is a name registered under the Pro-Electron numbering system.

The Pro Electron system is the European type designation and registration system for active components, such as electronic tubes and cathode ray tubes, semiconductors, liquid crystal displays, sensor devices, etc. providing concise and unambiguous type designations. The system provides integrity of the designations, and creates transparent and unique product identification, thus preventing confusion in the market place.
All Pro Electron type numbers consist of a prefix followed by a serial number. The prefix, generally two or three letters, clearly classifies the devices into categories with a sub-classification into classes, series or families. The next page summarizes the PRO ELECTRON numbering system. 
A few examples of devices registered under the Pro Electron system are:

BC557, BC857, BC847, CNY17-4, BFW11 & BPW34 are a few other devices registered under this system. Some of the Integrated Circuits registered under this numbering system are:

digital IC; PC family; operating temperature range -40 to +85 °C; serial number 1105; plastic leaded chip carrier.
digital IC; GM family; operating temperature range 0 to +70 °C; company number 74LS00A; ceramic DIL package.
analog IC; operating temperature range
non-standard; serial number 1000; plastic DIL package.

Transistor Variants:
  • BC547 : NPN Through hole (TO-92 Package)
  • BC557 : PNP Through hole (TO-92 Package) Complimentary to BC547

  • BC847 : NPN Surface Mount (SOT23 Package)
  • BC857 : PNP Surface Mount (SOT23 Package) Complimentary to BC847
BC847 and BC857 are SMD versions of BC547 and BC557

Lower breakdown voltage versions (ending in 8):
  • BC548 is a lower voltage version of BC547
  • BC558 is a lower voltage version of BC557

  • BC848 is a lower voltage version of BC847
  • BC858 is a lower voltage version of BC857
Higher breakdown voltage versions (ending in 6):
  • BC546 is a higher voltage version of BC547
  • BC556 is a higher voltage version of BC557

  • BC846 is a higher voltage version of BC847
  • BC856 is a higher voltage version of BC857

If you are an undergraduate engineering student studying in India and looking to build a project using any of these components, you can procure them from any of the electronic components retail shops that are there in Lamington Road, Mumbai. One of these is: Visha Electronics


Checkout this PDF (mirrors: link1 | link2 | link3) for a summary of the Pro-Electron numbering system.

The official booklet describing the complete Pro Electron System (15th edition 2008-01) can be obtained from:
Wikipedia article for Pro Electron is here.

About the other two numbering systems:

JEDEC System (wiki)
The other commonly used numbering system which one comes across is the JEDEC numbering system. 2N2222, 1N4007 and 4N35 are devices registered under this system. The device number consists of a digit, followed by the letter “N” and a serial number. The first digit is one less than the total count of useful electrical connections. Hence transistors (3 useful connections: Emitter, Collector, Base or Gate, Drain, Source) have ‘2’ as their first digit and Diodes (2 useful connections: Anode and Cathode) have ‘1’ as their first digit.
4N and 5N are reserved for opto-couplers. 
The serial number consists of two or more digits assigned consecutively, starting with number 21 for each class of device (1N and 2N are two different classes of devices).
If present, a suffix could indicate various things. For example, a 2N2222A is an enhanced version of a 2N2222. It has higher gain, frequency, and voltage ratings. Please check the device datasheet for its significance.

Instead of 2N and so forth, some manufacturers use their own system of designations. Some common prefixes are:
Motorola power, metal case
Motorola power, plastic case
Motorola low power, plastic case
Motorola HF, VHF and microwave transistor
RCA device
Texas Instruments (TI) power transistor, plastic case
TI planar power transistor
TI small signal transistor (plastic case)

The JEDEC Standard JESD370B “Designation System for Semiconductor Devices” is available at:

Japanese Industrial Standard
The JIS standard was based earlier on a standard JIS C 7012-1966 which has now been discontinued. In its place the standard EIAJ-ED-4001-1993 published by JEITA is now being used.

Some popular parts registered under this system are 2SA1187, 2SB646 (both are transistors). The part numbers under this system consist of a number followed by two alphabets and then a serial number. The system is summarized in the table below:

1st Number designates the type of device
 2 Letters
The following figures denote the device serial number
PNP HF transistor 
Serial number of component yields no indication of function or specification.
Since this is a serial number may provide insight into date.

A suffix after the serial number indicates that the type is approved for use by various Japanese organisations
Bipolar transistors
PNP AF transistor
FET devices
NPN HF transistor 

NPN AF transistor



Gunn devices 


P-channel FET/MOSFET 

N-channel FET/MOSFET




Signal diodes

Avalanche diodes


Zener diodes

Sunday, June 3, 2012

A simple thermopile

Here is a simple way of demonstrating seeback effect using common electronics lab materials:

  1. Cut out a square piece of single sided copper clad board
  2. Make vertical groves in it thereby separating the copper into isolated strips
  3. Take pieces of solder wire and solder each piece of solder wire on the non copper clad side of the PCB between the ends of two successive copper strip. (Look at the "Thermopile" Schematic here)
    If the solder wire you have are thin, you can twist two lengths together to increase the effective thickness like I have done.
  4. Dunk one end into pure ice cold water and heat the other end and observe the voltage across the ends of the circuit using a multimeter.