School of Systems Engineering. ORCAD Tutorial by Eur Ing Dr.

SE2P6 Engineering Applications (Anemometer Project) Project Supervisor: Dr Simant Prakoonwit www.reading.ac.uk/~sis04sp

School of Systems Engineering.

ORCAD Tutorial by

Eur Ing Dr. Simon Sherratt. Electronic Engineering

SE2P6 Engineering Applications (Anemometer Project)

Academic Year 2007/08 Project Supervisor: Dr Simant Prakoonwit

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1.1 LIST OF FIGURES ..................................................................................................... 4 1.2 LIST OF SYMBOLS ................................................................................................... 4 1.3 COMMONLY USED SCHEMATIC ICONS ..................................................................... 5 1.4 DESCRIPTION OF YOUR SYSTEM .............................................................................. 6 1.5 DESCRIPTION OF PSPICE ......................................................................................... 6 1.6 DESCRIPTION OF THE TUTORIAL PROJECT ............................................................... 7

2 STARTING YOUR PROJECT................................................................................. 8

2.1 TYPES OF PROJECTS ................................................................................................ 8 2.2 CREATING YOUR TUTORIAL PROJECT ...................................................................... 9

3 SCHEMATIC ENTRY OF THE CLOCK............................................................. 11

3.1 ENTERING COMPONENTS INTO YOUR SCHEMATIC WORKSHEET.................... 11 3.2 ENTERING THE CLOCK CIRCUIT ............................................................................. 11 3.3 EDITING THE TITLE BOX........................................................................................ 14 3.4 CREATING A CROSS REFERENCE (XRF) ................................................................ 15 3.5 CREATING A BILL OF MATERIALS (BOM) ............................................................ 16

4 MIXED MODE SIMULATION OF THE CLOCK CIRCUIT VIA PSPICE.... 17

4.1 DEFINING SIMULATION PARAMETERS ................................................................... 17 4.2 INVOKING PSPICE ................................................................................................. 18

5 SCHEMATIC ENTRY OF THE COUNTER ....................................................... 19

5.1 ENTERING THE COUNTER ...................................................................................... 19

6 MIXED MODE SIMULATION OF THE WHOLE CIRCUIT........................... 22

7 EXPORTING TO PCB............................................................................................ 23

7.1 TO CONNECT A POWER CONNECTOR...................................................................... 23 7.2 PCB FOOTPRINTS.................................................................................................. 24 7.3 ENTERING PCB FOOTPRINTS................................................................................. 25 7.4 GENERATING A LAYOUT NETLIST................................................................. 25 7.5 INVOKING LAYOUT............................................................................................... 26 7.6 WHAT IF THE ECO UTILITY REPORTS ERRORS?..................................................... 27 7.7 POSITIONING COMPONENTS .................................................................................. 27 7.8 DEFINING WHICH LAYERS AND TRACK THICKNESS TO USE.................................... 28 7.9 STARTING THE AUTOROUTER................................................................................ 28 7.10 CREATING A COPPER POUR.................................................................................. 28

8 PRINTING................................................................................................................ 29

8.1 FINDING THE BOTTOM LAYER. ............................................................................. 29 8.2 PRINTING THE BOARD DESIGN............................................................................... 29

9 OPTIONAL ADDITIONAL TOUCHES............................................................... 29

9.1.1 Pad resizing .................................................................................................. 29 9.1.2 Adding text. ................................................................................................... 29

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9.1.3 Increasing the size of the white box (route box) in Layout. .......................... 30

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INTRODUCTION

The aim of this booklet is to take you through the process of schematic capture, mixed mode simulation and creating a printed circuit board layout. You will be taken through each stage step by step in tutorial fashion.

This booklet will serve as invaluable reference material for the upcoming EA1 (anemometer) project and your electronic projects throughout your course.

Firstly, this chapter describes the Computer Aided Design (CAD) tools available to you. It then describes the generic process of simulation using Spice and finally describes a demonstration project that will be the theme for this tutorial. This project contains both analogue and digital components.

This tutorial assumes that you are familiar with Microsoft Windows, for example manipulating windows, printing, load, save and the mouse operations.

1.1 LIST OF FIGURES

.......................................................................... Page 1. Clock circuit for the tutorial project ............................................................ 10 2. The clock and counter circuit ...................................................................... 20 3. Adding a 2-pin power connector to your design ......................................... 22 4. Screen dump of the PCB rats nest layout (inverted image) ........................ 25 5. Positions of components altered to help the autorouter .............................. 26

1.2 LIST OF SYMBOLS

Button icon Description

Place a part from the current library or to add libraries to your project

Click this button to select the selection facility

Click this to place a generic ground. Be careful, as there are lots of types of ground. The simulator needs ground 0. IC's expect GND

Click this to connect your components with wires

Click this to place a DC power point in your circuit

Click this to place no-connects on you circuit. This is good practice to tell the schematic that you know nothing should be connected here

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1.3 COMMONLY USED SCHEMATIC ICONS

Component Description

R1220K

A 220KΩ (220,000Ω) resistor labelled R1

C3100n

A 100nF (100*10-9 F) capacitor labelled C3

D1OSCILLATOR

A diode which has had its type field changed to OSCILLATOR and its label is D1

V15V

A 5volt DC supply source labeled V1

0

A ground point labeled 0 (node 0)

VCC

Symbol to tie the connected node to a node termed VCC. Its use is to save on lots of wires, in your design, which would connect back to the supply.

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1.4 DESCRIPTION OF YOUR SYSTEM

The Electronic Engineering Division has been using CAD tools from OrCAD for many years. You will be using OrCAD for Microsoft Windows. OrCAD is very costly and probably the most comprehensive set of EE CAD tools currently available for the PC. However, you will only be using some of the features as:

• Schematic Capture. This is used to enter, or draw, your circuit on the PC.

• Mixed mode simulation. This is used to simulate the behaviour of your circuit. Mixed mode means that the simulator can operate on a circuit with both analogue and digital parts, unlike just an analogue simulator or a digital simulator.

• Automatic netlist extraction. This is the process of describing your schematic drawing in a standard textual form. This description contains what devices you have, what connections you have made and the types of packages (or Printed Circuit Board (PCB) footprints) you are using.

• Layout. This is the process of using the netlist description to logically connect the actual pins and wires of your components onto a PCB.

These software tools are available by clicking on Start / Programs / Cadence PSD where you will be presented with a selection of tools available to launch. The individual tools are described in the relevant sections below.

This tutorial does not yet cover the VHDL, FPGA (Xilinx etc), PAL, GAL, CPLD and digital simulation tools that OrCAD contains.

1.5 DESCRIPTION OF PSPICE

In this experiment, you will become familiar with the process of electronic circuit simulation (in-circuit emulation) using a common tool termed PSpice, but first a word about Spice.

For many years, the industry standard package for circuit simulation has been Spice, which was invented in the 1960’s. Spice is capable of predicting the behaviour of an

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electrical and/or electronic circuit. The first Spice used paper tape to describe the circuit. However, nowadays Graphical User Interfaces (GUI) within CAD tools enable the user to draw the circuit using a computer drawing package. The drawing is then textually described and passed into the Spice package for simulation.

A Spice package written for the PC is termed PSpice and many companies offer various PSpice simulation packages. You will be using the PSpice tool within OrCAD. You will be using the schematic capture tool to enter your schematic (circuit drawing). When instructed to do so, the computer will invoke the automatic netlist extraction to create a numerical description of your drawing (termed a netlist). The netlist file and a user specified simulation parameter file will then be passed to PSpice for mixed mode simulation. Once you are happy that your circuit is working, then you commit the design to a PCB layout with a high degree of certainty that it will work.

1.6 DESCRIPTION OF THE TUTORIAL PROJECT

In this tutorial, you will be simulating and generating a PCB layout of a mixed mode circuit (i.e. a circuit with both analog and digital components). For this tutorial, the actual circuit does not matter. What is of importance is the process of capture, simulate and PCB design methods described in the tutorial.

In order not to distract from the learning process, the circuit chosen is very simple and should not take up too much of your time. The circuit is based on a 555 timer IC to form a clock. The clock signal is then passed to a 74 series 393 IC that contains 2 separate 4 bit counters. You will be using one of these counters to drive 4 LED's. The LED's will turn on describing the count sequence.

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2 STARTING YOUR PROJECT

You may start your project on any of the EE PC's that have access to the OrCAD

2.1 TYPES OF PROJECTS

There are 4 types of projects that OrCAD has to offer. These are:

• Analogue or mixed mode circuit design. This is the type of project of interest for this tutorial.

• PC board. You select this type of project if you want to target your project straight to a PCB design.

• Programmable logic project. You select this type of project if you want to target your project as a CPLD or FPGA design. The project will configure libraries based on the vendor (manufacturer) you choose to target.

• Schematic. You select this type of project if you want to create a project that is NOT specifically targeted for vendor specific devices or PCB.

The purpose of specifying your project is to tell OrCAD what libraries of components you will need. However, you may change your project and add libraries later in the project.

*** When you do the Anemometer project, you will be selecting the Schematic project.

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2.2 CREATING YOUR TUTORIAL PROJECT

Click on Start, Programs, Cadence PSD, Capture CIS.

If a license error is reported then the OrCAD Network FlexLm license server is unavailable. If this happens then contact a member of staff to restart the server.

Click on File, New, Project…, and then

− enter My tutorial in the name box (or what you would like to call it)

− Select Analog or Mixed-Signal Circuit wizard(or A/D depending on version)

− In the location box, i.e. where to save the project, Click Browse.

− Select the N; drive.

− Create an Orcad folder for present and future designs.

Then click on OK to create the project.

In the Create Pspice Project box that appears, click on Create a blank project.

You are now presented with 2 windows, a smaller project window which has your title, My tutorial.opj, showing the files, and a much larger, blank graphical worksheet (SCHEMATIC 1: PAGE 1) for laying out your circuit diagram.

Click anywhere on the Schematic worksheet to select it (the window title bar will go blue) and a set of buttons will appear on the far right hand side on the Capture window.

Click on the Place Part button .

The project will then require a set of libraries to be selected that contain electronic components. You need the following libraries. (add them by clicking the >>Add button):

− analog.olb

− source.olb

− anl_misc.olb

− 74ls.olb

− opto.olb

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As you don’t need some of the default libraries, remove the other libraries:

e.g.

− connector.olb

− system.olb

Once you have all the 5 required libraries in the 'Use these libraries' window we are ready. Don’t worry if you have a design and later decide that you need a component that is not in your selected library list, as you can add and remove libraries later.

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3 SCHEMATIC ENTRY OF THE CLOCK

In this section, you will be drawing just the clock part of your circuit using the capture tool.

3.1 ENTERING COMPONENTS INTO YOUR SCHEMATIC WORKSHEET

In line with common practice, you will be entering your circuit in 2 parts, firstly the clock oscillator and then the counter. You will enter the clock circuit, simulate it and then enter the counter part, which will be clocked by the clock circuit you previously entered.

3.2 ENTERING THE CLOCK CIRCUIT

The clock circuit diagram for you to enter is shown in figure 1.

0

U1555alt

1

2

3

4

5

6

7

8

GND

TRIGGER

OUTPUT

RESET

CONTROL

THRESHOLD

DISCHARGEVCC

R2220K

R1220K

C10.47u

C3100n

C210n R3

220

D1MLED81

V15V

Figure 1. Clock circuit for the tutorial project.

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To place a component, click anywhere on the Schematic worksheet to select it (the window title bar will go blue) and a set of buttons will appear on the far right hand side

on the Capture window. Click on the Place Part button .

To place a resistor: From the place part window, just select the Analog library (by clicking on it) and then scroll down the parts list window and select the R part. A resistor symbol should appear. Click OK and place the resistor on your worksheet, by clicking it. When it is placed, another component will automatically appear. You may either press the Esc key on the keyboard or click the right hand mouse button and select End mode.

To edit the resistor: You will need to rotate the resistor by selecting an area around the resistor (it goes pink) and clicking on Edit and Rotate.

To change the properties of the default resistor click on the Select button, . Double-click on the 1K property, just next to the resistor, to change the resistance value from 1K to 220K or 220 depending on which resistor you are entering and then click OK. The resistor should now have 220K next to it with label R1. In schematic terms, each component needs a label, but it does not matter what the label is (as long as all the labels are different). Therefore, you may have different component labels from those in figure 1. However, if you wish, you can edit them by double-clicking on a component (not the label), select the parts tab on the bottom of the property editor, edit the part reference box then close the window. You have the usual copy and paste facilities. However, this will place at least 2 components on the worksheet with the same label. You will need to alter the label number so as two components don’t share the same label.

To place a capacitor: Place a capacitor in the same fashion as the resistor, by selecting part C and changing its value from 1n to 10n, 100n or 0.47u depending on what capacitor you are entering.

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To place the 555 timer: Place the 555 timer IC onto the worksheet in the same fashion as above, but the 555 component is termed 555alt in the anl_misc library. Notice that the component is mirrored in figure 1, which may be done by selecting the component on the worksheet and then rt-click on it and Mirror Horizontally.

To place a voltage source: Place the DC voltage source in the same fashion as above, but the voltage source is termed VDC in the source library. Make sure you change the value from 0v to 5v when you have the battery on the worksheet. ( Click away form the component, then double-click over the 0V).

To place an LED: Place the LED in the same fashion as above, but the component is termed MLED81 in the opto library.

To place a Ground:

To place a ground symbol you click on the GND button, , select the source library, and select the 0 component. See the paragraph below:

A word about grounds: Important

PSpice expects to measure voltages from node 0. Therefore, it is common practice to refer to node 0 as 'ground'. This does not have to be the case and many ground symbols and terminologys exist. As we will see later, Integrated Circuits expect their ground to be node GND.

Moving components You may click on components, keep the mouse button down and drag components around the worksheet.

To connect up your with wires Unconnected components have a square box around the area where the wire is to

connect. To place a wire, click on the Place wire button, . You must place the wire into the connection box, rather than just on the symbol. For example:

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R3220

R3220

R3220

Unconnected resistor with boxes around the connection points.

Properly connected resistor.

Resistor with an incorrect wire connection. Here, the wire is not terminated at the end of the resistor and the wire has just ended over the resistor. In this case the wire is NOT connected to the resistor.

3.3 EDITING THE TITLE BOX

Go to the bottom right hand side of the schematic window where you will find a title box (you may need to scroll). Double-click on the word <title> and the property editor will appear. Enter your name in the title field and it will appear in the title box. You may now print (scaled to paper size) your schematic and it would be a good idea at this point to save.

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3.4 CREATING A CROSS REFERENCE (XRF)

Its often a good idea to have a list of components, their values and a note of where OrCAD is getting the simulation details for individual components. This is done by creating an XRF.

To do this, you must go to the project window. This can be done either by clicking on 'Window' and then select the window with your project name.opj (opj stands for OrCAD project) or by clicking on the .opj window itself.

Click on the .dsn file (this is your design file holding the schematic file), click on 'Tools' and then 'Cross Reference...'. The Cross Reference Parts window will appear.

As the default settings are adequate, just click on OK. OrCAD generates an .xrf file, which you may view by double-clicking on the outputs folder in the project window, and then double- clicking on the .xrf file.

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3.5 CREATING A BILL OF MATERIALS (BOM)

Underneath the Cross Reference option, there is a Bill of Materials option. Here, Capture will analyse your circuit and give a textual file that you might use for ordering components from a manufacturer. To create the BOM, select the window with your project name.opj. Click on the .dsn file, click on 'Tools' and then 'Bill of Materials...'. The BOM is also stored in the outputs folder of the project window as a .bom file.

You can view its contents by double-clicking on it.

Example BOM.

Bill Of Materials May 21,2002 16:37:35 Page1

Item Quantity Reference Part

______________________________________________

1 1 C1 0.47u

2 1 C2 10n

3 1 C3 100n

4 1 D1 MLED81

5 2 R1, R2 220K

6 1 R3 220

7 1 U1 555alt

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4 MIXED MODE SIMULATION OF THE CLOCK CIRCUIT VIA PSPICE

Before the PC simulates your project, you must tell the simulator what type of simulation to do. When you invoke PSpice, the netlist of your circuit will be automatically created and passed to PSpice along with your type-of-simulation information.

4.1 DEFINING SIMULATION PARAMETERS

Select the schematic window by clicking on it. Click on PSpice and then New Simulation Profile. Enter a name for your simulation parameters, e.g. “sim 1” (it doesn't matter), and then click on Create. Then:

Click on the analysis tab and

− Set analysis type to Time Domain (Transient)

− Run time 2 (meaning 2 seconds)

− Start saving data after 0 seconds

− Make sure that the box 'Skip the initial transient bias point calculation' has a tick in it

Click on the options tab and

− Click on the Category: Analog Simulation

− Make sure that the box 'Use GMIN stepping to improve convergence' has a tick in it

− Click on the Category: Gate-level Simulation

− Initialize all the flip flops to 0 *** important***

− Set the Default I/O level A/D interfaces to 2 *** important***

Click on OK to finish your definition of the type of simulation you want to perform.

PSpice now knows how you want to simulate your circuit but it does not know what voltages or currents you are interested in. To do this, click on PSpice, Markers, Voltage Level and place a marker on the output wire of the 555 (connects the 555 to the LED).

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Once the markers are attached to a wire then they should change colour, from black to grey.

Out of interest, also place a voltage marker on the wire to pin 6 of the 555. This is only for you to see the operation of the circuit.

4.2 INVOKING PSPICE

To simulate the circuit, click on PSpice, Run. Your schematic is automatically saved.

If all is well, the PSpice window will appear and you should see the simulation being calculated. A graph window will appear within the PSpice window (which you may maximize) and you should see the square wave output of the 555 timer of period 0.214 seconds (0.143 seconds for the mark and 0.071 seconds for the space). You should also see the charge/discharge curve of the capacitor.

If all is not well, then:

1. Check that you have done all of the above actions (particularly PSpice simulation parameters).

2. Check the circuit is wired correctly and the component values are correct.

3. Try to interpret the error reports.

4. If you are in a class, contact the demonstrator. If not, ask for help from the staff in the lab, or help from your colleagues. It’s a good skill to be able to fault find!

Experiment with your simulation ! Change the capacitor value, re-simulate and you should see that the output frequency changes.

Once you are happy with the simulation procedure, change your circuit back to how it was in figure 1, re-simulate to check its OK and then proceed to the next section.

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5 SCHEMATIC ENTRY OF THE COUNTER

The second part of this tutorial is a digital counter, the 393 chip from the TTL family. This chip actually has 2 separate counters in the same package and each counter is 4 bits. We will use the 555 square wave output to clock the 393, such that for each positive edge (or rising edge) of the square wave clock input, the 393 counts up 1 state.

The output of the 393 will drive 4 LED’s to indicate the count state.

5.1 ENTERING THE COUNTER

On the schematic worksheet, click on the Place Parts button, click Libraries, and pick the 74ls library. Select the 74ls393 and place it on the sheet as per figure 2.

As stated, there are 2 counters per 393 chip. To bring up the second counter, place another 393 (as per figure 2), double-click on the second chip and change:

− Its part reference to the same as the first 393 you entered, e.g. U2B.

− Its Designator to part B (click on the designator window and pull down part B).

− Close the Property Editor window.

You should have the same U number for each chip and a part A and B on the worksheet.

OrCAD does not default to showing the power pins on integrated circuits (as do some packages). If you double-click on part A, scroll along horizontally on the Property Editor window and place a tick in the ‘Power Pins Visible’ box and close the Property Editor window. You now are presented with the power pins of the chip.

Important Notice that the power pins do not have a box to connect wires to. The power pins are just for show! OrCAD gives names to the power pins of your chips. If chips share the same name for their power pins then OrCAD will know they must be connected.

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All you have to do is place a power point in your worksheet for each power pin label and connect it to the proper voltage. In the 74 series case, all 5v power pins are termed VCC, while all ground power pins are termed GND. So we have to put a power symbol in our worksheet termed VCC and connect it to 5V. Place a ground symbol onto the other end of the 5v supply and label this symbol GND. Therefore, our circuit has 1 ground, but it is labeled both GND and 0.

Placing the VCC power point

To place a power point, click on the Place Power button, , select the CAPSYM library, and select the VCC symbol. Enter the symbol onto the worksheet just above the battery and connect it. Thus all VCC power pins on the IC's will be connected to this point, i.e. 5V.

Placing the GND power point

To place a ground symbol you click on the GND button, , select the source library, and select the 0 component (as before). Enter the symbol onto the worksheet next to the 0 ground symbol as per figure 2. Double-click on the 0 next to the new ground symbol and change its name from 0 to GND. Thus all GND power pins will be connected to this point, i.e. 0V. Important If you don’t put VCC and GND power connection points, then the PCB layout tool won’t know where to connect the power pins for IC's.

Placing the LEDs Enter 4 LEDs and resistors to the output of the 393 part A, in the same fashion as in section 3.

Wiring the circuit Connect the circuit as per figure 2, not forgetting that the unused counter (393 part B) should also be connected. The output of the unused counter may be connected to no-connect points, which specify that you know that the output is no-connect,rather than you have forgotten to connect that part of the circuit.

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The no-connect may be found by clicking on the Place no-connect button,

, and placing a no-connect onto the outputs of the unused 393. After correctly wiring your circuit, no pins should be unconnected, i.e. have a thin square box next to them.

0 GND

VCC

R1220K

R2220K

U1555alt

1

2

3

4

5

6

7

8

GND

TRIGGER

OUTPUT

RESET

CONTROL

THRESHOLD

DISCHARGEVCC

C210n

C3100n

C10.47u

R3220

D2BIT 0

D3BIT 0

D4BIT 0

R6220

R5220

D5BIT 0

R4220

U2A

74HC393

714

1 3456

2G

ND VC

CA QAQBQCQDC

LR

D1MLED81

U2B

74HC393

13 111098

12

A QAQBQCQDC

LR

R7220

J1

CON2

12

V15V

Figure 2. The clock and counter circuit

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6 MIXED MODE SIMULATION OF THE WHOLE CIRCUIT

You have already specified how you want the circuit to be simulated. By adding the counter, the circuit should still be simulated in the same fashion.

Now all that is needed, is to place a voltage marker on the QA output (pin 3) of the counter, (if you wish, you may remove the marker on pin 6 of the 555 IC). Run the simulation as before, and you should see that the output on QA is running at half the rate of the counter.

You may place voltage markers on QB, QC and QD to see the count sequence. Is this simulation what you expect, remember the binary count sequence?

Check that the period of the QD is correct (16 clock pulses wide).

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7 EXPORTING TO PCB

You have now entered the schematic and tested (simulated) to check the circuit operates as you expect. We do, however, need to add a connector to the schematic so that you can connect power supply wires to the PCB.

7.1 TO CONNECT A POWER CONNECTOR

The battery symbol is just a voltage source to simulate the circuit. We need a connector on the schematic to connect power to the PCB (power may be supplied by a battery or power supply unit).

Click on the place part button and you will see that no connector library exists. We

need to add a library by, clicking on add library, go up a directory level (use the ), double-click on Connector. In the Part window, select CON2. Place CON2 part onto your schematic, mirror horizontally, and connect in parallel with the battery as per figure 3.

This will place the appropriate ‘pads’ to solder some wires to on the PCB.

0 GND

VCC

C3100n

J1

CON2

12 V1

5V

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Figure 3. Adding a 2-pin power connector to your design

CON2 does not have a PSpice library associated with it, so your simulation will still run and not have been changed.

7.2 PCB FOOTPRINTS

Each component has a physical size and needs to be soldered onto to the PCB. A PCB footprint defines the space and placing of the pins of the component onto the PCB. There are 2 standards, footprints for metric packages (i.e. millimeters) and footprints for imperial units (i.e. inches). We are using imperial.

The footprints we will be using are: JUMPER100 JUMPER200 AX/.500X.125/.034 RAD/CK05 CYL/D.200/LS.100/.031 (NOTE NOT ….../0.031) DIP.100/8/W.300/L.400 DIP.100/14/W.300/L.800

LED footprint 2 pins spaced 0.1 inches apart power connector 2 pins spaced 0.2 inches apart all resistors 2 pins spaced 0.5 inches apart for horizontal mounting 10nF and the 100nF capacitors 2 pins spaced 0.2 inches apart for vertical mounting 0.47uF capacitor 2 pins spaced 0.2 inches apart for vertical mounting and the package is cylindrical in shape. The leads are 31 thou in diameter. Standard 8 pin Dual Inline Package (DIP). Pins 0.1 inch apart, width 0.3 inches and length 0.4 inches. Used for the for the 555 IC Standard 14 pin Dual Inline Package (DIP). Pins 0.1 inch apart, width 0.3 inches and length 0.8 inches. Used for the for the 74ls393 IC

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7.3 ENTERING PCB FOOTPRINTS

Obviously, before you design your PCB, you need to know the type of packages you will be using.

To tell OrCAD Capture what footprint each package has, double-click on each component in turn, bringing up the Property editor window. In the PCB Footprint, type in the footprint you require.

For this project use the footprints defined on the previous page. Some symbols already have the footprint entered. Make sure you enter the whole footprint description (including the decimal places).

Just to check, why not re-simulate your circuit. It should still work, as all you have done is to enter some more data in fields associated with components that are not examined by PSpice.

7.4 GENERATING A LAYOUT NETLIST

A Layout netlist is required to convert from the schematic into a form that the Layout tool (PCB package) can understand. This has the same format as the netlist generated for PSpice, but this has the footprint information as well.

Go to the project window and click on the project file (it has the project name and .DSN after it). Click on Tools, Create Netlist, then

Select the Layout tab, Make sure the Run ECO to Layout box is ticked. (Engineering Change Order) Select user properties are in inches Click OK.

Capture will then compile a binary netlist file (.MNL) describing your circuit for import into the Layout tool.

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7.5 INVOKING LAYOUT

Click on Start, Programs, Cadence PSD, Layout Plus.

In the layout tool, Click on:

− File, New,

− To open the Default template for the pcb’s size and shape, click in the “Look in” box.

− Follow the path; Win2K(c:)/Cadence/PSD_14.2/Tools/Layout_plus/data/default.tch. *** When you do the Anemometer project, you will be selecting the ANEMOMETER.TPL file. This has been done for you to simplify the layout.

− The Load Netlist Source window opens.

− Browse to find N:\ Orcad \ project name.mnl (the netlist you created earlier) and then click on the project name.mnl file and Open it.

− Just click on save to save your board’s layout, (even though it’s blank to start with) to your project directory with the name project name.max.

The Automatic ECO utility will start examining your netlist. It may take a few seconds to a minute. If there are no errors then the ECO utility should finish and leave you with your PCB layout looking something like figure 4. If ECO reports errors, go to the next section.

Figure 4. Screen dump of the PCB rat’s nest layout (inverted image)

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As can be seen from figure 4, all your components are laid out onto the PCB worksheet with what is termed rat’s nest wiring. These wires are not physical, but rather logical connections that the Layout tool knows about and will have to connect. You can also see the PCB footprints and individual pads (circular and rectangular locations that components will be soldered to).

7.6 WHAT IF THE ECO UTILITY REPORTS ERRORS?

The only errors that normally exist are that you have not entered a footprint for each component on the Capture schematic or that you have entered the footprint text incorrectly. Close Layout and go back to Capture. Make the changes, then run Layout again. Alternatively, a footprint library has not been loaded. In which case, use the Add Library button and search in c:\Program files\ Layout\library for the .llb file, which may contain the required footprint.

7.7 POSITIONING COMPONENTS

Move the Vert + Horiz scroll bars so that the components mostly fit into the Route box (white frame). Click on each component and drag it to where you want it to be, for example see figure 5. Try to place the components to minimize the rat’s nest, (the number of wires that cross). To do this you may also rotate the components when selected (use the 'R' key).

Click on the component. It goes purple. Roll it with the mouse rather than drag.

Figure 5. Positions of components altered to help the autorouter.

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7.8 DEFINING WHICH LAYERS AND TRACK THICKNESS TO USE

Click on View, Database Spreadsheets… and then Layers. Individually select the GND, POWER and all inner layers to “unused” routing by double-clicking on the Layer type field for each layer and selecting unused routing. (You may also select a block using the mouse like you do in Excel !) Set the Top layer to a Jumper layer (i.e. manual links you would put in) and the Bottom layer to Routing. This tells the autorouter to only use the bottom PCB layer. In a double-sided board design, both the Top and Bottom layers are set to Routing. Close the layers spreadsheet.

Track Thickness.

Click on View, Data Spreadsheets… and then Nets. Here, you can change the thickness of the tracks that will be laid down to make the connections. In order to make a good PCB using the University facilities, a minimum of 20 (20 thousandths of a inch) for each track, 30 or 40 is better. You may make the power wires (node 0 and VCC) a little bit thicker, 50, if you wish. You may select all or a block of the nets in the min con max field with the mouse, right click on the mouse and select properties…, enter 30 for the Min, Conn and Max and boxes, click OK and all the tracks change. Close the Nets spreadsheet.

7.9 STARTING THE AUTOROUTER

Click on Auto, Autoroute and then board. After routing, all sweeps should be completed. If not, then the autorouter can't place a track. If this is the case then click on Auto, Unroute, board and move the components apart. Having thicker tracks may prevent the process from completing, if so go back to 20 thou’.

You should be able to do a design with only routing on the bottom layer (i.e. a single sided board). To check that all routes have been placed, click on View, Data Spreadsheets… and then Statistics. The % routed should be 100%.

7.10 CREATING A COPPER POUR

Click on the “Obstacle Tool” icon. Move your pointer over to one corner of your board and right click on the mouse. Select “New” from the pop-up menu. Move your mouse around to each corner of the board (left click on each corner). This should draw a box around your board. When you have finished drawing the box, right click again and select “properties” from the pop-up menu. The “Edit Obstacle” box should appear. Select the following option in the “Edit Obstacle” box:

Obstacle type: Copper Pour Obstacle Layer: Bottom Clearance: 0.03 Net: 0

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Then press OK. Now right click again and select “End Command”. Orcad should now grow your track to fill the available space. 8 PRINTING 8.1 FINDING THE BOTTOM LAYER.

Printing will print a “top view” of the PCB, including the text for all the component names and details.

However, we want just the tracking to be laid down in copper when the board is manufactured. Any other marks may short tracks together. Go to Options, Post Processing Settings. Click on *.BOT, the rest of the line will highlight, now rt click, choose Preview. Close the Post Process box. This should reveal the tracking in blue. Bear in mind, what you see is a top view of the bottom layer. Notice that to help with orientation, pin one of any IC is marked with a square pad.

8.2 PRINTING THE BOARD DESIGN The final print, for manufacturing here, needs to be done on tracing paper.

Click on File, Print/Plot, put a tick in box for “Keep Drill Holes Open”, then print.

NOW back-up your work !

9 OPTIONAL ADDITIONAL TOUCHES 9.1.1 Pad resizing

Pads are generally too small and will be drilled away. To increase a pad size … File, library manager, click on library TM-Axial. In footprint box, click on AX/RC05. Up comes the picture of the footprint. Left click on the pad (it goes dark). Right click on it, click Properties = edit pad Click drop-down box in Padstack name. Select 120R100. OK. Place the pad. Create a new library to save it in, and then it’s easily transportable. Save As AX/RC05 plus your initials, e.g. AX/RC05BLAH. Close

9.1.2 Adding text. You may wish to identify your board such that it shows on the copper layer, alongside the tracking.

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Click on Tools menu, then Text, New…, which opens the Text Edit box. Type in your Text String (perhaps your initials ?). Put a tick in the Mirrored box. This will make a top view, looking down onto the board, back to front, but when viewed from underneath will read as normal. Select the Layer as Bottom, OK The text string is now rolling with the cursor. Click to place it. To move it, click on it again. 9.1.3 Increasing the size of the white box (route box) in Layout.

The maximum size is 500x500 units, (5 inches).

Click on Options, Route strategy, Route sweeps. Double-click Win/Comp/Man and specify route box. Change the X,Y to 500.

Edited ND Sept. 03

Edited SAS Aug 04

Edited RSS Sept 06

Edited SP Sept 07

School of Systems Engineering. ORCAD Tutorial by Eur Ing Dr.

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Transcript of School of Systems Engineering. ORCAD Tutorial by Eur Ing Dr.