This lab is due 5:30PM Tuesday November 2, 2010 at 115 Hackerman Hall

Transcription

1 M.E Lab 7: Printed Circuit Board Design Louis L. Whitcomb Department of Mechanical Engineering G.W.C. Whiting School of Engineering The Johns Hopkins University This lab is due 5:30PM Tuesday November 2, 2010 at 115 Hackerman Hall Reading: Your lecture notes. Get-started guide for ExpressSCH available at the course web site. Get-started guide for ExpressPCB available at the course web site. Design tips guide for ExpressPCB available at the course web site. Spec sheets for the following components: 1. ULN2803A Darlington array, 18-Pin DIP, Digi-Key Part ND Pin IC Socket, Mill-Max Part # Ohm or 470 Phm Resistor Network, 10-Pin SIP. 470 Ohm part is Bourns Part #4610X LF, Digi-Key Part 4610X-1-471LF-ND Series 0.1 inch header connectors, 3M Part # pin F-F ribbon cable Digi-Key Part A9BBG-1008F-ND uf Electrolytic capacitor, Panasonic Part #ECA-1CHG Green LED, Panasonic Part #LN31GCPH. 8. Red LED, Panasonic Part #LN21WPH. 9. Resistors from lab supply bench (see drawer labels for part numbers) Pin screw terminal connector, Phoenix part # Banana Jack, Pomona part #3267, Digi-Key Part # ND. 12. Phillips-Head Machine Screw, zinc plated steel, #4-40 3/8 (#4 diameter, 40 threads per inch pitch, 3/8 inch shaft length), Building Fasteners Part #PMS PH. 13. Lock washer, internal tooth, zinc plated steel, #4 (#4 diameter), Building Fasteners Part #INT LWZ Hex Standoff, zinc plated brass, 4-40 x 3/8 (4-40 internal thread, ¾ inch length), Keystone Part #1656A. Use your web browser to obtain the specification sheets for components not available on the course web site. Most will be available Apparatus: Components listed above. Micrometers for measuring component dimensions. Spec sheets for the components listed above. ExpressSCH and ExpressPCB CAD programs are installed on the lab PCs and are available for download here: Custom components files installed on the lab PCs and available in a single zip file at the course web site. This laboratory Louis L. Whitcomb Page 1 of 6

2 In this lab you will design a printed circuit board for the step motor controller circuit of the previous laboratory. We will select one student design for fabrication. In a later lab you will build and test this PCB. Your circuit should control and have status LED s for one step motor. If you want some more experience, add support for a second step motor. You will first use the ExpressSCH CAD programs for circuit schematic design and then use the ExpressPCB CAD program for printed circuit board layout. These programs are installed on the lab s PCs. Also installed on these PCs are several custom components which you may find useful for your design. Custom components for ExpressSCH are located in this directory Win XP/2K: My Documents\ExpressPCB\SchComponents_Custom Win Vista/7: Libraries\Documents\ExpressPCB\SchComponents_Custom with the following file names: 1. ULN2803.s 2. Connector_10_Pin.s 3. Connector_05-Pin.s Pin RSIP.s Custom components for ExpressPCB are located in this directory Win XP/2K: My Documents\ExpressPCB\PCBComponents_Custom Win Vista/7: Libraries\Documents\ExpressPCB\PCBComponents_Custom with the following file names: 1. 2-Pin_Screw_Terminal_Connector.p 2. 5-Pin_Screw_Terminal_Connector.p Pin_Screw_Terminal_Connector.p 4. 5-Pin_Ribbon_Connector.p Pin_Ribbon_Connector.p o A zip file of custom components is available on the course web site. You can install them on your PC if you want to work on this design at home. o Use the laboratory session to work on your circuit board design, measure component dimensions, and get help from the instructor and TAs. o In lab, you may work independently or with up to one partner. o If you work with a partner, you can jointly work on your schematic and PCB design, and each hand in a hardcopy and electronic copy of a single design. o Use your web browser to obtain the specification sheets for components not available on the course web site. Most will be available o Save a copy of the PDFs of each spec sheet for your future reference. Page 2 of 6

3 o Review the data sheets for the components you will use for this circuit board design. PCB design requires that you know the mechanical dimensions of the components and their pins as well as their electrical specifications. Data sheets for many of the components are available on the course web site. Components and micrometers are available in the lab for you to measure actual component dimensions. o Create a bill-of-materials spreadsheet of data for the entire parts list of your design. For each component, your spreadsheet should contain at least the following data: Part name (e.g. UN2803) Part designation (e.g. U1) Manufacturer Manufacturer Part Number Vendor Vendor Part Number Part Quantity Unit cost Total cost this part Your spreadsheet should assume a production volume of 100 units, and compute the total cost and unit cost at this production volume. o o o Use the ExpressSCH program to design a circuit schematic for your step motor control circtuit, which you prototyped in the previous laboratory. Note the following points: The schematic, defines the electrical circuit but does not define the actual physical layout of the circuit. IC Pin positions in a schematic are generally not in agreement with the actual physical layout. Use the snap to grid function to facilitate an organized schematic, but remember that a schematic is NOT a mechanical drawing. All external connections to the board are made through external connectors with labels like J1, J2, and J3. The drawing uses symbols for +5V and ground connections. Identical symbols indicate a common electrical connection between the signal symbols. Omitting the actual wiring for symbol signals simplifies the schematic drawing. When your design is complete, use the FILE > Check schematic for netlist errors function to check for errors such as unconnected pins and wires. Each component should have a designation: J1, J2, etc. for connectors and jumpers. U1, U2, etc. for ICs C1, C2, etc for capacitors R1, R2, etc. for resistors RN1, RN2 etc for resistor networks Use your circuit diagram from your step motor lab while designing the circuit schematic. Use ExpressPCB to lay out a circuit board for your circuit. Page 3 of 6

4 You may choose any board size. In general, smaller boards are less expensive. If the design is too small, however, it may be difficult to assemble. Use FILE > Link schematic to PCB to link your PCB design to your circuit schematic. This enables the PCB program to show you which pins need to be connected. Use a two-layer board design. Generally try to use one layer for horizontal circuit traces, and the other layer for vertical traces. You can connect traces on opposite sides with through-holes. Components connect to the board with plated through-holes. You, the designer, must determine the appropriate diameter and spacing for these holes by consulting the component spec sheets and/or measuring the components with a micrometer. Make a new custom PCB component for each of the two through-holes which will accept the banana clip sockets. The component should be comprised of (a) a through-plated hole with ID of inch and OD of inch, designated as pin #1 in the object properties and (b) a label such as GND or +12V. Select these two items, group them together as a new custom component, and give the component a name such as J3 or J4 corresponding to the component label in your schematic. Don t crowd components too close together. Do place capacitors near the respective ICs or connectors Use the snap to grid function to facilitate an organized layout. Remember that the PCB layout IS a mechanical drawing. All features have dimensions and tolerances. The fabrication method we ill use is likely to be two layer, with no silkscreen layer (i.e. the yellow silkscreen layer showing in your layout will not be reproduced in the actual board. Use the top metal layer for any labeling, but be sure not to short out any signal lines with your labels! Be sure to label the board with your secret code, date, and version number. What to hand in: 1) Lab Report: Your lab write-up should contain the following items: a) A standard lab cover sheet. b) A brief written description of how you designed this circuit. This should be a brief stepby-step account of the process, written with sufficient detail that another student could use the description to replicate the process. You should write this up independently from your partner. c) A color printout of your circuit schematic. d) A color printout of your PCB layout. e) A spreadsheet bill of materials spreadsheet for your design, as noted previously, computing total cost and unit cost for a quantity of 100 units. You and your partner can work independently OR collaborate to complete the circuit schematic, the PCB layout, and the bill of material. Page 4 of 6

5 It is OK (provided that you both contributed substantially to the work) for you each hand in the same circuit schematic, the PCB layout, and the bill of material. It is also OK for you to each do independent designs. 2) You and your partner should one copy of your final schematic and PCB files to Put the following words in the subject line: Subject: Lab #7 Files from Student <your code> and <your partner s code> for example: Subject: Lab #7 Files from Student 123 and 145 If you and your partner prefer to do independent designs, then you can each send independent files. Remember to note your and your lab partner s secret code on your lab report. Note your lab station on your lab report. Typed or hand-written lab reports are OK. Messy or ambiguous reports are not ok! Please clean up your workstation to perfection when you are done. Page 5 of 6

6 Cover Sheet for Lab #7: Printed Circuit Board Design Use this cover sheet for your lab writeup. My Secret Code: My Lab Station: My Partner s Secret Code: Lab Station Clean! TA s Signature & Date: Your TA will sign here after you have finished your lab, cleaned up your lab station to perfection, and shown your lab station to your TA. Page 6 of 6