4.3.1 Preparing and Interpreting Technical Drawing

Information Sheet 4.3.1 Draw and identify correctly electrical / electronic schematic One of the features of a quality electronic diagram is its appearance with simplicity and design and easy to understand layout., To do that, you have to observe the following rules in laying out electronic diagrams. Rules in drawing electrical schematic diagram:

1. The position of a symbol in a diagram does not affect its meaning. 2. The weight of a line used in drawing a symbol does not affect its meaning. . ! given symbol may be drawn in any si"e that is suitable for use in any  particular diagram. #owever, when a symbol is enlarged or reduced in si"e, it should be drawn in proportion to the rest of the drawing. $. %f necessary for contrast, some symbols may ba drawn smaller or larger than the other symbols in the diagram. #owever for simplicity, it is recommended that not more than 2 different si"es of symbols should be used in in the drawing. &. ! connecting line should be brought to a symbol either vertically or hori"ontally,  but a connecting line brought to a symbol at an angle has no significant meaning unless otherwise noted. '. The arrowhead of a symbol may be open or closed unless noted. (. The standard symbol for terminal )o* may be added to any symbol. +ut when this is done, the terminal symbol should not be considered a part of the symbol itself. Figure 1

Symbols used to represent various components in an electronicelectrical diagram:

 ote- hen more than one symbol of a specific type of component appears on a diagram, the letter/s is/are followed by numbers that identify the components. This combination of  letters and numbers is referred to as eference Designation.

Figure !

"ethods of Indicating Reference #esignations and $omponent %alues:

Figure 3

&umerical %alues of $omponents:

1. !ll resistors are e0pressed in ohm )* unless noted. actor 3nit 5 15 arad  15 6illi ' 15 6icro 8 15  ano 12 15 9ico

4ymbol  m 7 n p

Figure 4

2. !ll capacitors are e0pressed in microfarads )7* unless noted. arad : the unit of capacitance. %t is named after 6ichael araday. The farad measures how much electric charge is accumulated on the capacitor. actor 3nit 4ymbol 5 15 arad   15 6illi m ' 15 6icro 7 8 15  ano n 12 15 9ico p Figure '

Suffi( )etters 4uffi0 letters are used to identify separate parts of a unit upon a diagram when such components appear as single.

Figure *

)ine +hic,ness - ;ine conversion is used in drawing electrical/electronic diagrams

Figure 

$onnecting )ines < lines connecting symbols and other parts of on a diagram should be drawn vertically or hori"ontally. !s a general rule, no more than  lines should be drawn to any point on a circuit diagram. This procedure reduces the possibility of line crowding that could ma=e the interpretation of a diagram more difficult to interpret.

ecommended

!void if possible

Figure /

#ashed )ines  < )<<<<* are used on schematic and other types of diagrams to show a mechanical lin=ages between components or parts of components.

Figure 0

)ayout < The layout or form of a diagram should show the main features prominently. The parts of diagram should be carefully spaced to provide an even balance between  blan= spaces and lines. >nough blan= space should be left in the areas near symbols to avoid crowding any necessary notes or reference information.

Figure 1

Schematic #iagram of an 2udio 2mplifier

+as, Sheet 4.3.1 #irections: 3sing the electronic template, redraw the schematic diagram of a si0
arts )ist:

1 < '

?

22@

( < 12

?

8@

1

?

155@

1$

?

2.2@

1&

?

'.A@

1'

?

'A@

1(

?

1@

B1 < B'

?

157 / 1'C

B( < BA

?

$A7 / 1'C

1

?

24B8$&

&ame: 

#ate:   

5rade )evel: 

Score:   

6valuation2ssessment +est I - #irections: 2nswer the following 7uestions. 8rite the letter of the correct answer. 1. %f the Eree= letter omega )* appears in a schematic diagram, the component value  being represented is a. Bapacitor c. Transformer    b. Transistor d. esistor 

2. The labels of a capacitor B1! and B1+ in diagram are e0amples of a. Designated letters c. 4ubscript letters  b. 4uffi0 letters d. Boefficient letters . These types of lines ares used in schematic diagrams to show mechanical lin=ages  between components. a. Dashed lines c. Thic= lines  b. 6edium lines d. Thin lines $. One of these is OT given in a schematic diagram a. iring specifications c. !ctual appearance of components  b. 9oint to point resistance values d. Operating instructions &. The symbols on a schematic diagram are arranges so that the diagram can be FreadG in this manner. a. Top to bottom c. ight to left  b. +ottom to top d. ;eft to ight Test %% < Bomplete the table by identifying the symbols that represent the following components in a schematic diagram. $omponents $lass #esignated )etters

1. esistor  2. Diode . Transformer  $. Bapacitor  &. Transistor 

+est III - "atch the electronic and electrical symbols in column a with the corresponding descriptions in columns 9. 8rite the letter of your answer on the space provided before each number.

Bolumn !

Bolumn +

 HHHHHHHHHH 1.

!. Bapacitor 

 HHHHHHHHHH 2.

+. Transistor 

 HHHHHHHHHH .

B. Transformer 

 HHHHHHHHHH $.

D. use >. esistor 

 HHHHHHHHHH &.

. Diode

2nswer ey: +est I 1. !. 3. 4. '.

d b a c d

+est II 1. R  !. # 3. + 4. $ '. ; +est III 1. 6 !. F 3. 2 4. 9 '. $

Information Sheet 4.3.!

%dentify correct drawingI select and use equipment according to Job requirements

To produce a quality and mar=etable electronic diagram, you have to follow the >lectronic Drafting 4tandards which is the process of illustrating various =inds of circuits and wiring systems. 6ost symbols that we will encounter in laying out electronic diagrams are accepted as standard but in some cases, some manufacturers modify symbols and practices to suit a particular industry policy while others use their own symbols to represent unique or  special component and devices.

Schematic Symbols of 6lectronic $omponents

Figure 1

6lectronic +emplates

Figure !

#rawing Instruments and +heir
1. #rawing 9oard < ! smooth board usually rectangular in shape provided with  perfectly straight edge which is used as a wor=ing edge on which the T<4quare is moved while ma=ing drawings.

2. +-S7uare < it consists of two parts namely the stoc= and the blade Joined together at right angles to each other by means of screws. The stoc= is made to slide along the wor=ing edge and the blade moves on the drawing board. The wor=ing edge of a T< 4quare is used to draw parallel lines, vertical lines or inclined lines at 5 or '5 degrees.

. Set S7uares < 4et 4quares are generally made from plastic material. They are triangular in shape with one corner, a triangle. ! pair of set squares )5 o<'5o* and $&o. They are used to draw lines at 5o, '5o and $&o vertical or hori"ontal.

$. rotractor < 9rotractors are used to mar= or measure angles between 5 and 1A5o. They are semicircular in shape and are made of plastic. 9rotractors with circular shape are capable of mar=ing and measuring 5 to '5o, also available in the mar=et.

&. #rawing encils  < The accuracy and appearance of a drawing depends on the quality of pencil used to ma=e drawing.The grade of a pencil lead is mar=ed on the pencil. #+ denotes medium grade. %ncrease in hardness is shown by the value put in front of # such as 2#, # etc. 4ofter pencils are mar=ed as 2+, + and $+ and etc. ! pencil mar=ed + is softer than 2+ and pencil mar=ed $+ is softer than + and so on.The beginning of a

drawing may be mar=ed with # or 2#. or lettering and dimensioning, # or #+ pencils are used.

'. $ompass  < ! compass is used for drawing circles and arcs of circles. The compass has two legs hinged at one end. One of the legs has pointed needle fitted at the lower end whereas the other end has provision for inserting pencil lead.

(. #rawing ins and $lips < These are used to fi0 the drawing sheet on the drawing  board.

A. 6lectronic +emplates < these include symbols for electronic and electrical designs that can be traced using a drawing pencil.

+as, Sheet 4.3.! #irections:  3sing the different drawing instruments, draw the schematic diagram of a 5
Schematic #iagram of a 3-watt 2udio 2mplifier

&ame:  5rade )evel: 

#ate:    Score:   

6valuation2ssessment #irections - Draw at least & drawing instruments, describe and give their functions. Drawing %nstrument Description 3se 1. 2. . $. &.