Electromechanical Drawing
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Electromechanical Drawing Chapter 4 - Drawings: Show Me a Plan Copyright © 2004 by Janna B. Gallaher Drawings: The Language of Engineering Electronic Fabrication Drawings (The 10 Drawing Set) Design Drawings Working Schematic Drawing Conceptual Design PC Board Design Layout Drawing PC Board Artwork & Fabrication Drawings PC Assembly Drawing Wiring (Interconnect) Diagram Sheet Metal or Packaging Drawing Final Packaging Drawing Design Drawings System (functional) diagram Conceptual circuit design Packaging plan Conceptual Design Sketch System Diagram These drawings represent the “top level” design of a system. They show the functionality of the product. Only the functions are shown and their relationships. These drawings represent the “form, fit, and function.” Conceptual Electrical Design Important calculations show design intent. Note the sketches of the component packages and pin-outs. Conceptual design contains all the electrical requirements. Working Schematic Drawing Drafted schematic with all details Contains all of the electronic and electrical design information on a circuit Contains a representation of all parts and their values, their interconnection, and may contain test points or other waveform descriptions Most important document because it describes how a circuit works Working Schematic Drawing (continued) Rules for Drafting Schematics Flow should be from left to right, top to bottom Lines should be evenly spaced apart Lines between components should take the shortest path (but not diagonally) Connecting lines should have a minimum of crossovers and joggles Arrange long parallel lines in groups Avoid 4 way tie points or 4 way junctions Power supply lines should go up and ground lines should go down Negative voltages should be positioned below ground Working Schematic Drawing (continued) Poor Spacing Good Spacing Three examples of how to handle joggled,crossover and parallel lines. Note the difference in readability between the upper left diagram and the other two. Good Emphasis Working Schematic Drawing (continued) Connection Crossover, no connection Outdated Method A Connection B Connection of four lines Crossover Most Preferred Method Four methods of drawing junctions and crossovers. Note that method “C” is the most preferred. C No connection D Dot was forgotten Working Schematic Drawing (continued) Notes Notes give specific instructions, clarify issues, or define general specifications on the drawing. Component Designations Component Reference Designations are required for all components. They are sequentially numbered starting at the upper left and proceeding left to right and top to bottom. Locate each reference as close to the component as possible and centered around it. Typical component designations: C = capacitor, L = inductor, R = resistor, CR = diode, VR = zener diode, Q = bipolar transistor, 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.). They contain as much detail as possible about how the designer thinks it should look, operate, feel, and work. Usually these drawings are cluttered with thoughts and are usually sloppy and almost, but not quite, to scale. They will often be significantly revised as the project progresses. Generally, the sketches that contain a lot of cluttered notes and details are the most successful at being implemented. PC Board Design Layout Drawing Printed Wiring Assembly drawing shows all components mounted on the printed circuit board along with notes clarifying assembly techniques and general specifications. Printed Circuit Board drawing defines all of the parameters and requirements for the vendor to manufacture the p.c. board. PC Board Artwork The artwork is used to make a photo-tool used in manufacturing the printed circuit board. (Modern vendors use the 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 component interconnections along with any connections to the printed wiring assemblies. Sheet Metal or Packaging Drawing Final Packaging Drawing The packaging drawing defines how all of the assemblies and offboard components fit inside the enclosure.
