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Electromechanical Drawing
Chapter 4 - Drawings: Show Me aPlan
Copyright © 2004 by Janna B. Gallaher
Drawings: The Language of EngineeringElectronic Fabrication Drawings (The 10Drawing Set)
Design DrawingsWorking Schematic DrawingConceptual DesignPC Board Design Layout DrawingPC Board Artwork & Fabrication DrawingsPC Assembly DrawingWiring (Interconnect) DiagramSheet Metal or Packaging DrawingFinal Packaging Drawing
Design Drawings
System (functional) diagramConceptual circuit designPackaging plan
Conceptual Design Sketch
These drawings represent the “top level” design of a system. They show the functionality of the product. Only thefunctions are shown and their relationships. These drawings represent the “form, fit, and function.”
System Diagram
Conceptual Electrical Design
Conceptual design contains all the electricalrequirements.
Note the sketches of thecomponent packagesand pin-outs.
Importantcalculationsshow designintent.
Working Schematic DrawingDrafted schematic with all detailsContains all of the electronic and electrical design informationon a circuitContains a representation of all parts and their values, theirinterconnection, and may contain test points or other waveformdescriptionsMost important document because it describes how a circuitworks
Working Schematic Drawing (continued)
Rules for Drafting SchematicsFlow should be from left to right, top to bottomLines should be evenly spaced apartLines between components should take the shortest path(but not diagonally)Connecting lines should have a minimum of crossovers andjogglesArrange long parallel lines in groupsAvoid 4 way tie points or 4 way junctionsPower supply lines should go up and ground lines should godownNegative voltages should be positioned below ground
Working Schematic Drawing (continued)
Poor Spacing Good Spacing
Good Emphasis
Three examples of how to handlejoggled,crossover and parallel lines.Note the difference in readabilitybetween the upper left diagram andthe other two.
Working Schematic Drawing (continued)Connection
Crossover, no connection
Connection
Connection of four lines
Crossover
No connection
Dot was forgotten
OutdatedMethod
Most PreferredMethod
A
B
C
D
Four methods ofdrawing junctions andcrossovers. Note thatmethod “C” is the mostpreferred.
Working Schematic Drawing (continued)
Component Designations
Notes
Component ReferenceDesignations are required for allcomponents. They aresequentially numbered startingat the upper left andproceeding left to right and topto bottom. Locate eachreference as close to thecomponent as possible andcentered around it.
Notes give specific instructions,clarify issues, or define generalspecifications on the drawing.
Typical component designations: C = capacitor, L = inductor, R = resistor, CR = diode, VR = zener diode, Q = bipolartransistor, U = integrated circuit, SW = switch, F = fuse
Working Schematic Drawing (continued)
Conceptual Design Sketch
Conceptual Design Sketch
Conceptual designs start out as sketches on whatever is handy (paper, napkin, table cloth, hand, etc.). Theycontain as much detail as possible about how the designer thinks it should look, operate, feel, and work. Usuallythese drawings are cluttered with thoughts and are usually sloppy and almost, but not quite, to scale. They willoften be significantly revised as the project progresses. Generally, the sketches that contain a lot of clutterednotes and details are the most successful at being implemented.
PC Board Design Layout Drawing
Printed Wiring Assembly drawingshows all components mounted onthe printed circuit board along withnotes clarifying assembly techniquesand general specifications.
Printed Circuit Board drawing definesall of the parameters andrequirements for the vendor tomanufacture the p.c. board.
PC Board Artwork
The artwork is used to make a photo-tool used inmanufacturing the printed circuit board. (Modern vendors usethe output of a p.c. design program to directly create “Gerber”files that plot directly on film to make the photo-tool.)
Wiring Diagram
The Wiring Diagram defines off-board componentinterconnections along with any connections to the printedwiring assemblies.
Sheet Metal or Packaging Drawing
Final Packaging Drawing
The packaging drawing defines how all of the assemblies and off-board components fit inside the enclosure.