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Design News, March 2013

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Design Hardware & Software Designer. Once on the page, enter what power is available at the source, the project requirements, and the designer will do the rest. Like any application in this category, WEBENCH will output a circuit completely designed to meet the needs. Of course, this is ultimately designed to sell chips and make profit for whomever; it will solve the job's power demands near instantaneously. Once created, the power supply "SPICE" model can be imported into Multisim. After adding this, a complete design is almost done without the need to design a circuit on one's own. Showing an auto routed circuit in Eagle CAD. I loaded one of the examples from the Eagle CAD example project pages. Two clicks of the mouse took me from schematic to PCB layout. Technically this could be printed and should work. It is a car battery monitor with LM3914 and HP HDSP4832 led bar graph. (Source: CadSoftUSA Eagle CAD) Electrical Design & Simulation Electrical design is not a mystical art form. It is similar to LEGOs, plug in the right components and the system will work, in theory. Software circuit design has advanced to a very high level of design, near drag-and-drop. Take National Instruments' (NI) Multisim. There is a model for almost every electrical component out there. Load in the parts, link them together, and create the circuit. Designing in Multisim is like building in real life but under ideal conditions. I will admit, designing a circuit takes a bit more knowledge to start than drawing in CAD. I will start out by saying, if this comes up a lot on the job, studying up on electronics is a must. Get some books on electrical design and an electrical engineer's handbook and also watch video tutorials. The "electrical wheel" has been invented many times and even in different ways. There is more than one way to switch for an LED, for example. A quick Internet search will show how many people handled certain problems. After someone's solution is searched, take the found circuit and reconstruct the model in Multisim. Then adjust the circuit to fit the job's requirements, if it doesn't. After a few of these "copy paste" circuits have been run through, building unique ones will be easy. The novice can now make circuits. For the more learned designer, Multisim is a perfect way to rapidly test the circuit. I suggest that a circuit be designed over and over digitally, before ever attempting an actual build. Since Multisim can simulate the circuit's operation in any time scale, seeing how it is all operating is a breeze. Some chip manufacturers have Web-based design tools that can construct all manners of circuits. One to focus on, and is the life's blood of any design, is a power supply design tools. Take Texas Instruments' WEBENCH Power PCB Layout Circuit design is finished after a successful simulation in Multisim or just using a manufacturer's examples or application notes. A physical board needs to be created and tested. Laying out a Printed Circuit Board (PCB) is not an intimidating, impossible option for the novice. Software is there to make the build as easy as possible. Like Multisim, and other circuit simulation tools, PCB design software often comes packing almost every single electrical component that has a SPICE model. The industry standard, OrCAD is worth a trial. However, for this section I picked CADSoft's Eagle CAD, a free PCB program. As the name indicates, designing a circuit is just like drawing parts in a CAD-like interface. In fact, it will look quite similar to Multisim or even SolidWorks. This should make for an easy transition from circuit concept to PCB. Lucky for those adopting Eagle CAD today, the tutorials are abundant. Everyone from affiliate sites to hacking communities has put together video series that can handhold an engineer to their first PCB in minutes. A YouTube search for "eagle cad" should do the trick. After one tutorial, drawing a simple schematic will be a hurdle pushed to the side. The tutorials will quickly advance to the PCB layout side of Eagle CAD since this is ultimately what the applications is meant to do for the user. One click will move from the circuit design to the PCB layout. Component placement on the PCB will have an effect of operation. Don't worry; simple circuits have a tendency to work no matter how the parts are placed. However, they may not work optimally. For the ambitious, take a look at the datasheets for the various components. Manufacturers will offer, in detail, the guidelines for PCB placement. Microcontrollers often have a few strict rules. The suggestions will often say a capacitor or an oscillation crystal can be no further than "x" from the processor leads. Different license levels of Eagle CAD will offer automatic features, like laying out the electrical traces between component leads. However, like CAD, simply drawing lines from the component pins to their matching end-points will complete traces, almost like connecting the dots. Design News | march 2013 | www.d esign n ews.com –60–

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