Month: February 2008

Building Printed Circuit Boards at home

I have seen several tutorials on the Internet for making professional looking PCBs at home. In fact, I attempted making a few last year with limited success. However, I managed to perfect the technique yesterday. The procedure I used is described in this tutorial.

I made some minor changes to materials and made a few perfect PCBs.  First of all, the quality of bare copper clad sheet is very important. There are two type of copper clad sheets available here (in Trivandrum):- Paper phenolic and Glass epoxy. Never use paper phenolic type for this technique.  The copper layer detaches itself from the paper phenolic substrate when you apply heat.

Secondly, clean the surface of the glass epoxy board using Brasso.  Brasso is available in hardware/stationary shops. Put 5ml Brasso on the copper clad sheet and rub it with cotton waste. The oxide coating on the board will be completely removed and its surface will become shiny. The paper I used is called “art paper” , as per the local store keepers nomenclature. A2 size sheet cost around Rs.5.

I printed the mirrored layout on a HP1020 printer at 600dpi. The iron was set at the maximum temperature range and heated for some 5 minutes. Then I fitted the printout on the copper clad and applied the iron for another 3 minutes ( until the paper turned slightly brownish) .  The board was them socked in water and I could peel of the paper. The pattern was perfectly transferred to the board.

I have observed the following while developing the procedure.

a) Cleanliness of the board is very very important. Give extra care to it if you ever attempt  making PCB at home.

b) Transfer the image as soon as possible after printing.

c) Keep the temperature of the iron maximum.

d) ( In Trivandrum, you should attempt it only after 2. AM in the morning.  Your power supply voltage will be 230v around that time.  Normally, I get 160 -190v during day time. So this condition applies to Trivandrum only 😀 😀 )

The art of Long Distance FM DXing

I will describe my experiences in receiving long distance FM here.

For receiving long distance FM (or FM Dxing) the first thing you need is a good radio. Good receivers are hard to find nowadays. If you can find a Phillips of Sony radio you are half way through. (I think Phillips no longer markets radios in India). There are several cheap Chinese radios available in the market. They are ok for a casual Dxer. Some radios today can automatically scan the FM band for stations. I don’t recommend them.

Next step is to build an antenna. There are several possibilities for this . Some of them are dipole. folded dipole or even a quad.

First let us see how to construct a simple dipole. The FM band is from88MHz to 108Mhz. We will design a dipole tuned at the centre of the FM band.( ie 98Mhz)

The formula for calucualting dipole length is =468/Frequency in Mhz.

I n our case the length works out to be 4.78 feet.

diple
Get hold of 2 pieces of copper wire.( If you cannot find, buy two pieces of 1/2inch aluminum rod or welding rod. As a ham I use welding rods for all my VHF antennas) . Fix them on a PVC pipe ( Use your ingenuity for fixing them. ) the Dipole antenna has an impedance of approximately 75 ohms. You can buy sufficient length of coaxial cable for connecting your dipole to the radio.

Fix the dipole at a good height. Keep it horizontal ( FM uses horizontal polarization ). The other end of the coaxial cable must be connected to the radio. Most of the modern radios use a telescopic areal. Fold it to the minimum position and fix the inner wire of the coaxial cable to th telescopic areal .The outer braid may be connected to the negative terminal of the battery.

Some of the older TVs used to have rabbit ear antenna. ( a small detachable dipole whit adjustable length) If you can locate one , it can be directly used as a dipole.

Your mileage may vary depending on your location,atmospheric conditions etc

I have seen folded dipoles and rectangular loops suitable for FM reception in some of the electronics shops in Trivandrum. They are mainly used here to receive Suriyan FM broadcasting from Tirunelveli. I don’t know whether they are still available.

Academic Projects

Kenney Jacob has written an article on academic projects here.

Most of his observations are true. Being a faculty member, I have seen this kind of activities in several institutions around Trivandrum. Just take a look at the local classifieds section of The Hindhu. You will see several ads promising students with things like real time linux embedded linux.etc.

I have joined my college very recently and I was asked to do evaluation of a few final year projects last month. Most of the projects were ready made stuff bought from some of these training companies.

Our department has a minor project in the sixth semester. Present sixth semester started in December 2007. I have insisted that all sixth semester projects must be done in the college lab itself. I don’t care if the minor project is really minor. But , I need some kind of contribution from every one in the project.

Consequently, some of them have take very simple projects. But, I will see to it that they design the circuit, simulate it , write the code if any and finally solder it themselves on home made PCBs.

Here is the advice I gave to some of my own students. Your project must be simple enough. I don’t expect any one to invent a new gadget or technology overnight. If you are daring, I dont mind you doing so. I suggest you to take up projects in emerging technologies. Make sure that you grasp at least the basics of your chosen topic ( at least by the end of the project). Do the project in a professional manner. Keep everything documented. If possible, start a home page/blog for your project and publish the report on internet.

You must work towards the completion of projects in the stipulated time. I don’t expect all projects to be completed as expected. There may the technical and practical hitches. Well, that doesn’t matter if you have done your home work and made a through study of your chosen area.

Most of the time you will get around 2 months for a projects. In between, most of you will get some kind of placement which will probably end your interest in academic activities. If you don’t complete a project due to your lack of interest , I can find it out quickly and I wont tolerate.

After this sermon, some of the guys in my college has made some progress. 😀

Here is another sentiment prevailing in student community:- most of the HR managers in companies like Infosys , or Satyam are not really concerned about what their engineers study at college. They just check, whether the guy can talk decent English and do basic arithmetic. Then why should I bother to study bla bla bla when my dad can buy it for me. After all he has bought me a seat in Engineering College.

FM war in Trivandrum

We , radio freaks in Trivandrum, had only one FM station till last week. Suddenly the FM band is abuzz with whole lot of activity. Today , I could tune the following stations.

Frequency Station
101.9 Ananthapuri FM
98.3 Radio Mirchi
94.3 Club FM
93.4 SFM
92.7 Big FM
( Frequency updated on 29th May 2008 , Big Thanks to Roy for pointing out the mistake).
The stations come with crystal clear stereo. I have been listening to them for the past 2 days. The program content is same in all the new stations.
I used to do a lot of FM dxing in the past. We can access lot of FM channels if you can put an external antenna. I have received kannur FM station and several SriLankan stations on my Philips Radio. I am writing a separate article on FM dxing .