|
AT /
Step 4: Using EAGLE to create a printed circuit board (PCB) layout from the schematicby Don Rhine Go back to the TEAMS EAGLE Home Page or to the 16.100 Intro to ECE EAGLE Home Page IntroductionWe'll go through this PCB layout exercise together in class on November 18th (you don't need to do anything beforehand, but you may try it on your own first, if you like). However, your EAGLE Mint Tin Amp schematic layout is due on November 18th!! If you would like to try the PCB layout process on your own, here are instructions for you to follow...please read each step carefully! If you missed a few points on the first part of the project, we are giving you an opportunity to demonstrate your knowledge and earn some bonus/extra credit. Here is a video of the EAGLE PCB layout process demonstrating the steps below How to create the printed circuit board using your schematic:1. Correct your schematic, if necessary... a. Review the Mint Tin Amp solution. Read the important notes in red!
b. Make sure you've added +9V, -9V, and PE (ground) symbols from the supply2 library (see notes in red from my solution).
c. Make sure you add the "Mint Tin Outline" and "9V_Battery_Outline" project boxes to your schematic (highligthed in yellow in revised parts list.
d. Carefully review your schematic to make sure it is complete and correct before moving on to the PCB layout steps below! In Particular, make sure all of the wire connections are correct using the show tool.
Be careful that your schematic is correct! I have reviewed a couple diagrams for students and have found many unconnected joints (they looked connected on the schematic, but were not). Try moving the components in the schematic--if connected, the wires should move with the components! Also, use the show tool!
2. On the top tool bar click on the Board/Schematic button. Eagle will ask if you want to create a new schematic—click yes. Maximize the window.  The parts on your PCB layout screen should look exactly like those shown to the right, although your parts may be in a slightly different order. For example, you should have ONE 8 pin DIP chip (the OPA2132PA amplifiers), ONE dual potentiometer that looks EXACTLY like the one below, etc. If they don't look the same, you chose the wrong part (go back to the schematic, delete the incorrect part, and add the correct one).
Note: Always use the Board/Schematic button to switch between the schematic view (a logical abstraction of the physical device) and the board view (a CAD representation of the physical layout of the printed circuit board). DO NOT use the MS Windows tabs on the bottom of the screen to flip between the windows--although I have never had a problem, I have heard that using the windows tabs can cause problems.
4. Let's assume that we will use a single-sided PCB (a layer of copper on only the bottom side of the fiberglass or composite board). EAGLE Light allows you to design single or double-sided boards, but in industry you will see boards with many layers "sandwiched" together as shown in the diagrams below (the diagrams came from this great site: http://www.ami.ac.uk/courses/ami4809_pcd/. The full version of EAGLE allows you to access these other layers for more complex projects. Take a moment to use the Identify ( I) tool to understand the concept of layers (you may also want to click into the View – Display/Hide Layers to see which layers you are seeing, and the physical meaning of those layers. A few important ones:
5. Move the components (individually or in groups) into the white rectangle (remember that you can rotate as well by clicking your right mouse button). This rectangle's physical size (try printing and measuring it) is 100 mm by 80 mm and represents the outer dimensions of your PCB (Layer 20). I recommend you start your layout within these large dimensions to get the circuit routing "neatly," then see if you can compress the design into a smaller area. This is an iterative process! Keep the components spread out a bit at first. If you try to move a component to an area outside of the 100 mm x 80 mm dimension rectangle (layer 20), an error will pop up and will bounce the component back into the 100 X 80 space. If you place components too close to the edge of the rectangle, you will constrain the routing of the copper wires. Note that you can use the Dimension layer (Layer 20) to create any PCB shape and constrain the routing in that particular shape (as shown in the Christmas tree PCB above). There are many other layers you can explore on your own that can give you more control over the design of a more complex PCB. 6. Use some logic as you place the components! It is helpful to place the components in the same relative location as you did on your neat circuit schematic. Keep in mind that you are make a device for a person to use, so some components needs to be place in locations easy for the user to access. Although your view of the board is in two dimensions, you need to think in 3D! 7. Use the Rats Nest tool often to "straighten out" the yellow unrouted wires before you run the auto router in the next step. Running the Rats Nest tool redraws wires to their closest possible connecting point. You may be able to see a better place for a component after you run the Rats Nest. 8. Use the auto router tool to turn your yellow wires (unrouted logical connections) into copper wires on the PCB (either red or blue wires for copper on the top and bottom of the board, respectively).
9. After routing is finished, see if any yellow (unrouted) connections remain (you will see 100% routed at bottom of screen if all wires were routed, and you will see no remaining yellow wires). If not 100% routed, use the Ripup tool or type ripup; then enter in the command line. Rearrange components in a logical manner, then try rerouting. 10. Repeat steps 6 - 9 to until you get a neat, compact design. You may want to try using the smash tool to reorganize component labels and value on your final design. 11. Finally, Use the Text tool to add your name, date, and a project title to your PCB. If you like, you could use the change tool to change the layer to Layer 16 and "write your name in copper." Go back to the TEAMS EAGLE Home Page or to the 16.100 Intro to ECE EAGLE Home Page |
