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Embedded Systems

Jan 12, 2016

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Embedded Systems. University of Belgrade School of Electrical Engineering Department of Computer Science. Authors: Gvozden Marinkovic [email protected] Nikola Milanovic [email protected] Goran Timotic [email protected] Ivan Sokic [email protected] Prof. Dr. Veljko Milutinovic [email protected] - PowerPoint PPT Presentation

  • Embedded SystemsUniversity of BelgradeSchool of Electrical EngineeringDepartment of Computer ScienceAuthors:Gvozden Marinkovic [email protected] Milanovic [email protected] Timotic [email protected] Sokic [email protected] Dr. Veljko Milutinovic [email protected]

  • IntroductionDesignComponentsMicrocontrollersCommunicationExamplesARMsPIC MCUs

  • DesignSpecificationCircuit DesignPrinted Circuit Board LayoutFirmwarePilot RunProductionAirBorn ElectronicsSource

  • Electronic Design FlowchartAirBorn ElectronicsSource

  • Specification Starts as collection of ideas that describe a device or productSpecifications go through two phasesfirst phase they describe the product as desired: must-have, bells and whistles featuressecond phase they describe the product as required: describes the product as it is required to be producedAirBorn ElectronicsSource

  • Specifying New DesignGive your project a nameKeep project name short, it saves timeDescribe your project (Opening Statement)Keep the first description shortFirst sentence should summarize the whole function of the projectDescribe or name equipment, devices or interfacesDescribe your projects marketDescribe the market need your product fulfillsEstimate the production volumeAirBorn ElectronicsSource

  • Specification:Technical IngredientsA Specification reads like a list of project features, describing the unit, and will usually include:InputsControlsOutputsIndicatorsFunctions Modes of operation Power SupplyCommunicationsProtectionFail safes and replaceable partsConnector typesPhysical format and size

    AirBorn ElectronicsSource

  • Circuit DesignMaps out the electronics and connections in the most readily readable formThe designer needs to do background work:research specifications of componentsresearch interaction between components (especially timing and loading) research physical packagesresearch arrangement of connector pinoutsThe finished circuit diagram is the main document for the design

    Part 1AirBorn ElectronicsSource

  • Circuit DesignCircuit diagram is a strict documentA circuit diagram must reflect the actual construction of the printed circuit board which is made from itPrinted circuit board CAD and Schematic CAD are tied together through a Net-checkThe circuit diagram references each part on the PCB with a designator and pin numbers for each connectionPart 2AirBorn ElectronicsSource

  • Printed Circuit Board LayoutConnections on the PCB should be identical to the circuit diagramCircuit diagram is arranged to be readablePCB layout is arranged to be functionalPCB layout can be performed:manually (using CAD)in combination with an AutorouterAirBorn ElectronicsSource

  • Methods of PCB constructionConventional Rigid PCB of thickness 1.6mmWire-leaded components mounted on only one side of the PCBAll the leads through holes, soldered and clipped.Easier to debug and repair than Surface mountPart 1AirBorn ElectronicsSource

  • Methods of PCB constructionSurface Mount Technology (SMT) devices (SMD) PCB with tag-leaded components soldered flush to PCB padsHoles are still needed on the PCB, not where the component leads are attachedGenerally smaller than conventionalGenerally more suited to automated assembly than conventionalPart 2AirBorn ElectronicsSource

  • Methods of PCB constructionSurface mount and conventional mix Most boards are a mix of surface mount and conventional componentsDisadvantages because the two technologies require different methods of insertion and solderingPart 3AirBorn ElectronicsSource

  • Methods of PCB constructionDouble sided LaminateTracks on both sides, normally with PTH holes connecting circuitry on the two sides togetherDouble sided component AssemblyMounting components on both sides of the PCBNormally only surface mount circuitry would be mounted on both sides of a PCB

    Part 4AirBorn ElectronicsSource

  • Methods of PCB constructionMulti-layerPCB Laminate manufactured with more than two layers of copper tracks, by using a sandwich constructionCost of the laminate reflects the number of layersUsed toroute complicated circuitrydistribute the power supply more effectivelyPart 5AirBorn ElectronicsSource

  • Methods of PCB constructionGold platedCertain areas on a PCB may be gold plated for use as contact padsFlexible PCBTechnique used extensively withmembrane keyboardscombination connector/circuit boardscircuit boards to fit in awkward shapesPart 6AirBorn ElectronicsSource

  • Methods of PCB constructionChip On Board (COB)IC is attached direct to a PCBBond out wires from the IC connect directly to PCB landsChip is covered with a black blob of epoxyUsed mostly with very high volume, cost sensitive applicationsPart 7AirBorn ElectronicsSource

  • Methods of PCB constructionPhenolic PCBPhenolic is a cheaper PCB laminate materialDaughterboardCircuit board mounted to another circuit boardPart 8AirBorn ElectronicsSource

  • Printed Circuit Board EtchingCAD File processingPCB CAD files are sent to the PCB ManufacturerPCB manufacturer inspects the files, making a drill list and adding identificationCAD files are processed and sent to a photoplotter to turn into film artwork AirBorn ElectronicsSourcePart 1

  • Printed Circuit Board EtchingLaminate drilling and electroplatingLaminates are drilled with holesDrilled laminates are coated in a chemical to enhance electroplating of holesLaminates are put in a copper plating bath, all the holes are electroplated This connects pads on opposite sides of the PCB, electrically

    AirBorn ElectronicsSourcePart 2

  • Printed Circuit Board EtchingLaminate etchingThe laminates are coated with a UV-sensitive photo-resist The track pattern is imaged onto each side of each PCB, using the photoplots and UV light The photo-resist is developed, leaving photo-resist only where copper is requiredThe laminates are put in acid, to etch away unrequired copper, forming the track patternThe bare copper PCB, with tracks and pads now finished, is cleaned AirBorn ElectronicsSourcePart 3

  • Printed Circuit Board EtchingLaminate solder masking and tinningThe bare copper PCB is silkscreened with a solder mask (usually green) The solder mask is dried or curedThe PCB is tinned - solder is applied to exposed padsThe PCB is levelled - bumps in the solder is made flat by using hot air or hot oil

    AirBorn ElectronicsSourcePart 4

  • Printed Circuit Board EtchingFinal stagesThe PCB is silkscreened with component identification lettering (usually white)The silkscreen legend is dried or curedAny final drilling is done of holes that are not to be plated through, any routing is done, and the laminate is cut into individual printed circuit boards

    AirBorn ElectronicsSourcePart 5

  • PCB AssemblyAssemblies should be maintainablerepairabledurable; andeasy to installAirBorn ElectronicsSource

  • PCB DocumentationFront Cover Title, date, version number, customer details, project features Schematic ECO Sheet Details of any circuit modificationsBill of material The parts listParts key A glossary of the part number abbreviations, with package sizes, lead spacing, tolerance notes and preferred types AirBorn ElectronicsSourcePart 1

  • PCB DocumentationFront panel artwork Manufacturing notes Contains the notes relating to previous production runs - for instance problems encountered, methods of testing Drilling diagram Showing the positioning and size of every hole on the PCBActual size PCB overlay Showing the positioning and identification of the PCB componentsThe plan is printed actual size to allow components to be placed against it to check for fit

    AirBorn ElectronicsSourcePart 2

  • Firmware The major steps in Firmware design are:Program SpecificationProgram DesignWriting codeProgram Test AirBorn ElectronicsSource

  • Program Specification The specification for the Electronic Product being designed will usually also be the specification for the programming requiredThe program specification will required the writer to go into substantial detail about how the product actually operates, and how it is usedA thorough program specification leads straight in to Flow charts and timing diagrams, which are components of Program DesignAirBorn ElectronicsSource

  • Program DesignThe program design stage lays out the structure and algorithms of the firmwareThe structure and algorithms may be laid out as:flowcharttiming diagramdescription of a protocolmemory map; or equationAirBorn ElectronicsSource

  • Writing CodeIf the program is well specified and the algorithm design stage has been thorough, the actual code writing stage can become almost mechanicalBy defining the software at the outset, before code is written, a much more defined, integrated, set of code can be producedThe extra space occupied by comments costs nothing, and if the comments are well laid out there is no possibility that they can detract from understanding the code

    AirBorn ElectronicsSource

  • Program TestDivide the testing of the design into small, autonomous unitsIt is easier to detect faults before they are compounded by other factorsProgram testing requires getting diagnostic data out of the target, for analysisBy emulation tools, or through the hardware itself (for instance a serial port)AirBorn ElectronicsSource

  • Pilot RunTo test the product further, a Pilot run normally follows the prototyping stage Small quantity of units are field trialed in a beta testOpportunity to assess the manufacturability of the design, and the usability of the documentation

    AirBorn ElectronicsSource

  • ProductionFollowing the pilot run there will likely be changes to the firmw

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