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LSU 06/04/2007Electronics 81 CAD Tools for Circuit Design Electronics Unit – Lecture 8 Schematic Diagram Drawing Etched Circuit Board Layout Circuit Simulation.

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Presentation on theme: "LSU 06/04/2007Electronics 81 CAD Tools for Circuit Design Electronics Unit – Lecture 8 Schematic Diagram Drawing Etched Circuit Board Layout Circuit Simulation."— Presentation transcript:

1 LSU 06/04/2007Electronics 81 CAD Tools for Circuit Design Electronics Unit – Lecture 8 Schematic Diagram Drawing Etched Circuit Board Layout Circuit Simulation

2 LSU 06/04/2007Electronics 82 Schematic Capture Many CAD packages available for design, simulation, and layout. Will use ExpressPCB suite for example Extensive library of standard components Custom components can be created Does not include a simulation function

3 LSU 06/04/2007Electronics 83 After startup, maximize the window, choose View menu, then Zoom To Fit Pick out a library component, for example a 555 timer chip. View Help screens as needed ExpressSCH Main screen Component selection tools User’s manual and Quick Start Guide

4 LSU 06/04/2007Electronics 84 Click on the desired component. A cursor will appear. Position the cursor and click, the symbol will be added to the drawing. Click again to duplicate the symbol. Choosing Components from Menu

5 LSU 06/04/2007Electronics 85 Click and drag to move the component around the drawing Use the Zoom tool to get a closer look. Placing Components Zoom tool

6 LSU 06/04/2007Electronics 86 Choose Component menu, then select Component and symbol manager Using the Component Manager Component menu

7 LSU 06/04/2007Electronics 87 Choose Component menu, then select Component and symbol manager. Select a component, then click Insert into schematic. Using the Component Manager

8 LSU 06/04/2007Electronics 88 Right click on a component, then open the Set component properties window. Part ID and value can be set, as well as other properties. Component Properties

9 LSU 06/04/2007Electronics 89 Note U1 has numbered pins, Q1 does not. Pin numbers may be hidden. Click on a pin to view the pin number. A closer look at components Pin number display

10 LSU 06/04/2007Electronics 810 Left click at the start and at each desired corner. Right click when done. Adding a Wire Connection Wire tool

11 LSU 06/04/2007Electronics 811 Library components include symbols for power sources and ground (common) connections. Power and Ground NOT a connection IS a connection

12 LSU 08/12/2004Electronics 812 Components are created as groups of: Rectangles Lines Arcs Pins Creating Custom Components

13 LSU 06/04/2007Electronics 813 Draw the component. Assign pin numbers and names. Select the component. Access the Component menu and choose Group to make component. Assign component properties, such a ID and type. Custom Components line arc rectangle pin

14 LSU 06/04/2007Electronics 814 Afterwards, choose Save custom component from Component menu Component Properties

15 LSU 06/04/2007Electronics 815 Connect the custom component into the circuit. If desired, use Component manager to add the component to your Favorites list Ready for Use

16 LSU 06/04/2007Electronics 816 Circuit Board Layout After drawing the circuit with ExpressSCH, use ExpressPCB to design a pattern for an etched circuit board. Schematic can be linked to the board layout to aid in placing components and routing interconnections. Correct pin numbering will be essential.

17 LSU 06/04/2007Electronics 817 Top Layer – an etched copper pattern Bottom Layer – an etched copper pattern Silk Screen – an inked pictorial pattern Top and bottom layers may include Traces – a copper path interconnecting two or more points Vias – a connection between the top and bottom layers, with a continuous plated copper path existing through the hole Pads – a point where a component lead will be connected most pads exist on both top and bottom layers and incorporate a through-hole, thus also serve as a via. Boards Have Three Layers

18 LSU 06/04/2007Electronics 818 layer selection place a pad or via place a component place a trace Component patterns are saved arrays of pads which must match the shape of a physical component. It usually includes a silkscreen outline of the component. Custom components can be created, just as in ExpressSCH.

19 LSU 06/04/2007Electronics 819 Pad inner diameter sets the size of the through-hole. Must be large enough to accept the wire lead of the component. Outer diameter controls how much solder-accepting surface is available. OD = 0.062” and ID = 0.029” is a common pad for small components Pad Characteristics

20 LSU 06/04/2007Electronics 820 Trace width determines the amount of current the trace can carry without excessive voltage drop or heating. See Design Tips under the ExpressPCB Help menu for suggested trace widths. Examples: a 0.025” trace can carry up to about 1 amp a 0.050 trace is good for up to about 2 amps Trace Characteristics

21 LSU 06/04/2007Electronics 821 Design a one transistor amplifier, with capacitively coupled input and output. A protection diode should be used to protect the transistor from reverse polarity. A Very Simple Design Example

22 LSU 06/04/2007Electronics 822 First Draw the Schematic Diagram After all components are named and labeled, select Check schematic for netlist errors from the File menu. Leave this window open, then open an ExpressPCB window.

23 LSU 06/04/2007Electronics 823 Now Place All Components Don’t worry about connecting them with traces yet. Name each component to match the name on the schematic. Select Link schematic to PCB from File menu.

24 LSU 06/04/2007Electronics 824 Connect Components Together Use the Highlight net connections tool to identify which pads should be joined with traces. Blue dots indicate points that should be connected, according to the linked schematic Highlight net connections tool

25 LSU 06/04/2007Electronics 825 Connect Components Together Re-arrange the components for the most efficient interconnects. Highlight net connections tool

26 LSU 06/04/2007Electronics 826 Connect Components Together Re-arrange the components for the most efficient interconnects. Then add the traces. Use the bottom side as much as possible. This example uses much too much space. It’s just an illustration. Highlight net connections tool

27 LSU 06/04/2007Electronics 827 Activity Design a simple power supply using a three terminal regulator integrated circuit. Draw the schematic. Lay out a circuit board.


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