Homework 6: Printed Circuit Board Layout Design Narrative Due: Friday, February 22, at NOON

Transcription

1 Homework 6: Printed Circuit Board Layout Design Narrative Due: Friday, February 22, at NOON Team Code Name: RoboRubik Group No. _11 Team Member Completing This Homework: Erik Carron Address of Team Member: purdue.edu NOTE: This is the third in a series of four design component homework assignments, each of which is to be completed by one team member. The completed homework will count for 20% of the individual component of the team member s grade. The body of the report should be 3-5 pages, not including this cover sheet, references, attachments or appendices. Evaluation: SCORE DESCRIPTION Excellent among the best papers submitted for this assignment. Very few 10 corrections needed for version submitted in Final Report. Very good all requirements aptly met. Minor additions/corrections needed for 9 version submitted in Final Report. Good all requirements considered and addressed. Several noteworthy 8 additions/corrections needed for version submitted in Final Report. Average all requirements basically met, but some revisions in content should 7 be made for the version submitted in the Final Report. Marginal all requirements met at a nominal level. Significant revisions in 6 content should be made for the version submitted in the Final Report. Below the passing threshold major revisions required to meet report * requirements at a nominal level. Revise and resubmit. * Resubmissions are due within one week of the date of return, and will be awarded a score of 6 provided all report requirements have been met at a nominal level. Comments:

2 1.0 Introduction Our design project in the RoboRubik, a digital Rubik s Cube that uses LEDs to represent colored blocks unlike a normal Rubik s Cube that uses a mechanical system and colored stickers. There are 7 total PCBs in the RoboRubik, the main board and 6 side boards. Each face of the cube will have a PCB containing a pushbutton and 8 LEDs to represent the multicolored blocks of a normal Rubik s Cube. The main board in the middle contains the brains of the RoboRubik. PCB Layout Design Considerations Overall The size of the cube is our main constraint. The main board contains the heart of the design. It contains the microcontroller, the WiPort[2], the power circuitry, and the headers to the other boards. The side PCBs contain the Optek LEDs[3], the Allgero LED drivers[4], and the NKK pushbuttons[6]. The layout of the side PCB is important because it interfaces with the external enclosure of the RoboRubik. There is a pushbutton in the center of each board that will sit in a cutout in the enclosure and the 8 LEDs of each board needs to be in the correct location to represent the square blocks of a normal Rubik s Cube. Since all of our components are small and simple, we do not have to worry about too much current going through our traces. There are no analog signals to work with either in our project. The WiPort is the only thing that has analog and RF signals, but that is all self-contained in its own package. The only challenge the WiPort gave us was the footprint. It is a little difficult to work with because it is in a metal enclosure and the 40 pins are located on the bottom. The Integration guide was very helpful. 2.0 PCB Layout Design Considerations Microcontroller The microcontroller we are using is the MC9S12H128 [1] in the 48 pin package. This package is just like the one from our ECE362 demo kit. Since this microcontroller is so common, it was easy to determine the layout for it. The documentation is also very helpful. We used a basic oscillator circuit with 2 capacitors and a resistor. We kept this circuit as close as possible to the microcontroller. The other circuit needed was the power supply bypass capacitor circuit. We located this under the microcontroller on the apposite side of the PCB to keep it close to the clock pins. These were the only major considerations for our microcontroller. -1-

3 3.0 PCB Layout Design Considerations - Power Supply Our power supply circuit is very simple. Since we are going to power it with battery of 6 to 9 volts, we only needed to step down the voltage. We decided to use just a Fairchild LDO[5] regulator to take in the power voltage and drop it down to 3.3 V, the voltage all of our components run on. This circuit is located in the corner of the main PCB and does not require too large of traces. 4.0 Summary Overall our PCBs are very strait forward. The main consideration is keeping them as small as possible. The PCBs are unique because we are going to have 7 of them. There are 6 for the sides and a main one in the middle. The side layout is important because it interfaces to the user through a pushbutton and LEDs. The main board is also important because it contains the main components and is what will most likely limit the size of our cube. -2-

4 List of References [1] MC9S12C Family User Guide [Online document], [cited 2008 Feb 22], Available HTTP: MFA25%20-%20Freescale.pdf [2] Lantronix WiPort Integration Guide [Online document], [cited 2008 Feb 22], Available HTTP: [3] Optek OVSRRGBCC3 Datasheet [Online document], [cited 2008 Feb 22] Available HTTP: [4] Allegro A6279 Datasheet [Online document], [cited 2008 Feb 22] Available HTTP: [5] Fairchild KA378R33 Datasheet [Online document], [cited 2008 Feb 22] Available HTTP: [6] NKK Series CB3 Pushbutton Datasheet [Online document], [cited 2008 Feb 22] Available HTTP: -3-

5 Appendix A: Project Packaging Illustrations Figure 1 Main Board Schematic -4-

6 Figure 2 Side Board Schematic -5-

7 Figure 3 WiPort Interface Schematic -6-

8 Figure 4 Main PCB Layout (incomplete) -7-

9 Figure 5 Side PCB layout (incomplete) -8-