ECE 477 Digital Systems Senior Design Project Spring 2006 s2

ECE 477 Digital Systems Senior Design Project Spring 2006

Homework 6: Printed Circuit Board Layout Design Due: Friday, February 24, at NOON

Team Code Name: ____We Ate 9______Group No. __7___

Team Member Completing This Homework: ___Saad Sami______

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 10% of the team member’s individual grade.

Evaluation:

Component/Criterion Score Multiplier Points Introduction & Layout Considerations 0 1 2 3 4 5 6 7 8 9 10 X 3 Documentation for PCB Layout Design 0 1 2 3 4 5 6 7 8 9 10 X 5 List of References 0 1 2 3 4 5 6 7 8 9 10 X 1 Technical Writing Style 0 1 2 3 4 5 6 7 8 9 10 X 1 TOTAL

Comments:

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______ECE 477 Digital Systems Senior Design Project Spring 2006

1.0 Introduction

The No Glove No Love Project is a HID (Human Interface Device) designed to replace the wireless mouse. Worn around the wrist and the hand, the glove redefines how users interact with a computer. Typical mouse movements are obtained from the user through pressure sensors and accelerometers. Accelerometers on the wrist provide accurate tilt and movement measurements, and pressure sensors, placed on the underside of the fingers, emulate standard mouse buttons. Data from these components is captured at timed intervals, and sources of noise are reduced so as not to affect measurements. Once captured, the data is sent wirelessly to a base station through a 2.4 GHz transceiver module. Upon receiving the data, the base station encodes it into the standard Windows mouse protocol and delivers it to the PC through a low- speed USB interface.

2.0 PCB Layout Design Considerations Electronic circuits are always subject to noise. Noise can alter digital and analog signals within a circuit and thereby give invalid or distorted results. It is an unavoidable consequence, and through proper PCB design, it can be greatly reduced. Layout considerations for the No Glove No Love Project are structured around reducing EMI (Electro Magnetic Interference) and other forms of noise. The considerations are broken down amongst the two main components: the base station and the glove. The following paragraphs discuss packaging constraints, EMI reduction, trace size, and sectioning of the PCB as they relate to the base station and the glove. Design of the No Glove No Love project is dictated by its comfort to the user, therefore its size is very important. The PCB for the glove is around 4 by 2.5 inches and must fit on the wrist of the user. This size constraint limits the flexibility of the design. Routing of traces and placement of parts are crucial and are arranged to save on size. Surface mount parts are utilized for major components to further reduce on size and a battery connector allows for the battery compartment to be placed off of the PCB. General PCB design rule states that nothing is more important to circuit design than a solid and complete power system [1]. Many layout considerations revolve around the power system of the glove and the base station. As mentioned in [1] there are three types of signal grounding: single point, multipoint, and hybrid. [1] recommends single-point grounding for frequencies below 1 MHz, however, the glove and the base station will utilize multipoint grounding due to

-2- ECE 477 Digital Systems Senior Design Project Spring 2006 their higher frequencies of operation. Grounding on the base station is located near the USB Ground connector. On the glove the grounding connects to the negative terminal of the batteries. This serves as the primary ground for the entire circuit. As suggested by [1], the power and ground lines have wide traces and run parallel to each other. A copper pour is also introduced on both PCBs for shielding from the 2.4 GHz wireless transceiver modules. Stability of signals is an obvious concern. Through the use of power decoupling this issue is addressed. Capacitors are placed at the power and ground terminals of the ICs and they increase stability on the power and ground rails by filtering out noise. They are placed as close to the IC as possible as suggested by [1]. Bypass capacitors are also placed near the IC’s to provide instantaneous current on signal transitions. These capacitor placement schemes were utilized in both the glove and the base station. Sectioning of the PCB is also crucial in reducing EMI. The glove has seven A/D channels that are being utilized. To prevent interference and for proper placement, the digital and the analog components of the design are separated. The multipoint grounding scheme as described earlier allows for separation in these components’ ground returns [2]. On the glove, the inputs from the pressure sensors, the bend sensors, and the accelerometers are placed as close as possible to the microcontroller to reduce interference. A ground pour is also placed within the vicinity for further noise reduction. In addition the RF modules on both PCBs are placed away from the other components on the board and as suggested by the manufacturer, they are placed as far as possible from the ground plane on the PCB [3]. On the base station, the header for the module rests on the opposite end of the USB connector. On the glove, the RF module header is placed at the unconnected end of the battery module on the PCB. Ground and power traces are routed away from these modules so as not to affect their signals. On the base station, proper placement of the microcontroller’s clock circuitry is also of concern. Clock circuitry is usually the biggest generator of wide-band noise [1]. The circuit is placed as close to the MCU as possible so as not to generate interference. For similar reasons it is also located away from the wireless transceiver module. Due to the many modules used in the base station and the glove, header pins are added around the PCBs. Two eight pin headers are placed on the sides of the board to accommodate the accelerometer breakout boards. At the front of the board, three two-pin headers interface with the pressure sensors and the bend sensors. As mentioned earlier, the RF module is

-3- ECE 477 Digital Systems Senior Design Project Spring 2006 interfaced at the bottom of the board on the glove and opposing the USB connector on the base station. It uses a seven pin header. These additional I/O pins are subject to noise interference. The accelerometer breakout boards have onboard filters for their analog acceleration outputs. The bend sensors and the pressure sensors are basically potentiometers and as a design decision additional filtering was not added. As all signals are routed on traces, proper trace size and orientation can lead to further EMI reduction. The traces on the glove and base station are kept at the default 12-mil size. Power and ground traces are increased in width to handle the demands of the circuit. For ease of routing, power and ground traces from the regulator output and the USB interface are decreased in width to sizes between 25 and 40 mils. To decrease transmission reflections [2], traces which change direction turn at 135 degrees instead of 90 degrees.

3.0 Summary

Proper planning is the key to success in any project or design. By reflecting on the aforementioned considerations, problems in PCB design can be caught and addressed before the layout begins. The project and its’ main components, the base station and the glove, are no exception. This document discussed many PCB guidelines as they pertain to the No Glove No Love Project. Issues such as sectioning components

Be sure to read Motorola Application Note AN1259 (posted on course web site) before you begin your PCB layout.

-4- ECE 477 Digital Systems Senior Design Project Spring 2006

List of References

[1] Freescale. (2006) “Noise Reduction Techniques for Microcontroller-based Systems” http://www.freescale.com/webapp/sps/utils/SingleFaq.jsp?FAQ-2759.xml

[2] Freescale. (2006) “System Design and Layout Techniques for Noise Reduction in MCU- Based Systems” http://www.freescale.com/files/microcontrollers/doc/app_note/AN1259.pdf?srch=1

[3] Personal E-Mail. E-Mail from SparkFun employee on RF-MiRF suggestions. http://shay.ecn.purdue.edu/~477grp7/documents/RF-MiRF_Assistance.html

IMPORTANT: Use standard IEEE format for references, and CITE ALL REFERENCES listed in the body of your report. Provide “live” links to all data sheets utilized.

Appendix A: PCB Layout – Top & Bottom Copper

Figure A.1 – Top Copper Layer of Glove PCB

Figure A.2 – Bottom Copper Layer of Glove PCB

Figure A.3 – Top Copper Layer of Base Station PCB

Figure A.4 – Bottom Copper Layer of Base Station PCB

Appendix B: Routing Statistics Report

************************************************ * * * STATISTICS REPORT * * * * N:\BACKUP\GFINAL\SCHEMATIC\GLOVE_COPPER.MAX * * Fri Feb 24 09:49:23 2006 * * * ************************************************

STATISTIC ENABLED TOTAL ------Board Area 8.8 8.8 Equivalent IC's 9.7 9.7 Sq. inches per IC 0.92 0.92 # of pins 145 145 Layers 4 28 Design Rule Errors 0 0 Time Used 13:18 13:18

% Placed 100.00% 100.00% Placed 34 34 Off board 0 0 Unplaced 0 0 Clustered 0 0

Routed 95 95 % Routed 100.00% 100.00% Unrouted 0 0 % Unrouted 0.00% 0.00% Partials 0 0 % Partials 0.00% 0.00%

Vias 25 25 Test Points 0 0 Vias per Conn 0.26 0.26 Segments 432 432

Connections 95 95 Nets 32 32 Components 34 34 Footprints 67 67 Padstacks 42 42 Obstacles 171 171

Theoretical Dist 61.1 61.1 Routed Dist 63.3 63.3 Unrouted Dist 0.3 0.3

Document B.1 – Routing Statistics Report for Glove PCB

****************************************** * * * STATISTICS REPORT * * * * N:\BACKUP\BFINAL\BASEFINAL_COPPER.MAX * * Fri Feb 24 09:00:49 2006 * * * ******************************************

STATISTIC ENABLED TOTAL ------Board Area 5.4 5.4 Equivalent IC's 5.9 5.9 Sq. inches per IC 0.90 0.90 # of pins 89 89 Layers 4 28 Design Rule Errors 0 0 Time Used 8:35 8:35

% Placed 100.00% 100.00% Placed 17 17 Off board 0 0 Unplaced 0 0 Clustered 0 0

Routed 57 57 % Routed 100.00% 100.00% Unrouted 0 0 % Unrouted 0.00% 0.00% Partials 0 0 % Partials 0.00% 0.00%

Vias 24 24 Test Points 0 0 Vias per Conn 0.42 0.42 Segments 286 286

Connections 57 57 Nets 18 18 Components 17 17 Footprints 49 49 Padstacks 47 47 Obstacles 107 107

Theoretical Dist 30.6 30.6 Routed Dist 30.0 30.0 Unrouted Dist 1.0 1.0

Document B.2 – Routing Statistics Report for Base Station PCB