Helping Hand

HELPING HAND INTRODUCTION: Welcome to this new edition which is an extension to your favorite magazine Techno Te(a)ch. This edition will now cover some practical difficulties which are faced in the projects that are released lately. So hope this method of providing some very practical tips will help you to accomplish the works with in a short span of time and also maintaining the ‘standards’as well. Alright, now let’s go to this month’s tips and errata! BREAD BOARD: The bread board is a very basic instrument that is used to test a circuit which is at hand. It is very important because connections can be easily made and repaired in no time. The bread board has some basic ‘rules’to make its working smooth else, it will turn out to be an ultimate time consumer (not to mention patience). If u closely observe, the bread board has three main sections. The first section is the power rail. The power rail is located on the extreme ends of the bread board, thus, two such rails can be found per board. The usage of this rail can be used to supply different voltages to different parts of a same circuit. For example, an amplifier sometimes requires four sets of power supply. That is both positive and negative (+15V and -15V to +21V and -21V). If this is over your head then read the following paragraph carefully. The power rail is such interconnected that all the cells (that is what the small sockets to insert wires are called) are one single line connected. There will be a break in the rail indicating that the rail connection is broken. Thus, there are two sets are rail per row .The rails have 4 sections (totally) in a bread board. If your purpose is not using more than two power ratings then a rail can be connected by simple wire thus making the entire rail as one single connection. Now use this to supply the bread board from the rectifier circuit which was published in the previous editions. Connect in such a manner that the top rail carries the positive supply (+5V) and the bottom rail carries (GND). Do the similar modifications to the bottom rail. Never use the cells to power your circuits. It will confuse you at later stages when the circuit grows. Always use the power rails to supply power. You can follow the same procedure for the rail on bottom of the bread board. The second section is the normal connection system. It is seen that the bread board has columns and columns of cells. Each column is interconnected; it can be used as a single interconnected wire. Totally 5 cells form a column. Use it wisely to avoid misconnections. Never use too much wires it can confuse you. Instead use the component leads to establish connections. Not only it gives a very good look, also it enhances the working of the circuits (it’s called response. Ever heard of external disturbance or noise?). The third basic is the IC connection. There is a mid line that divides the board into two halves. Use it to fix the IC on either side of the board staying along the axis of the mid line. Then the IC can be powered from the rail and connections can now be made.

WIRING: SKILL OR CHALLENGE? It really depends what is your age in wiring. The length of wire stripping, the length of the wire both changes the connection pattern. There is also a method in stripping the wire. Being a single stranded wire it’s quite easy to strip it. If it’s a multi stranded wire then the job becomes tedious. Better get some practice and improve your accuracy, depth of cutting, length required, and many more. The cutting device is called a wire stripper. It has two handles and a very sharp cutting edge. There is also a small gap in the cutting edge. Place the wire in the small gap. Use your fore finger to limit the depth. To use it put the fore finger between the two handles and apply force slowly. The spring will resist your force try to push the handle and feel the depth using the fore finger. Now the sheath is cut. In order to slice it, without releasing the grip slide it out. The length should be optimum to insert in the cell. And the core should not be damaged by the cutting tool else the wire may be struck in the cell unable to remove forever. It can be justified that the wiring is both skill and challenge. Use your skill to face the challenge. ERRATA! This month’s decade circuit is posing some problems. In the clock circuit using IC NE555 please apply the following changes: connect a 1000 microfarad, 16V electrolyte capacitor. Remember the capacitor has polarity so connect the positive side to pin 2 and ground side to pin 1 which is already grounded (the ground in the capacitor is indicated with a very thick line on its wall). Instead of using 1K resistance between pins 7 and 2 use 10K resistance. In order to vary the clock frequency manually use 100K preset instead of the 1meg preset. Also use a 1k resistor in series with the preset to limit current flow. For the preset short the lower and the middle arm to use it wiper mode. (See circuit below). If you still encounter problems, then change the capacitor to a 3.3 microfarad, 16V electrolyte capacitor (same connection pattern as above), R2 to 3.9K and preset to 10K and retain 1K resistance. Also connect a 0.01microfarad capacitor of ceramic disk type (no polarity) between pin 5 and pin 1 (that is ground GND). The LEDs in the decade counter will glow randomly if the clock input is absent. So check the clock circuit for its speed. If there is any problem hindering your work please do report about that on our email id [email protected] or post a comment on www.eee0610.blogspot.com . all the beset for your projects!

1000µ, 16V

0.01µ