ARM Edition Sarah L Harris and David Money Harris Digital System Design Topics Introduction Component Selection Bill of Materials BoM Circuit Implementation Breadboarding Printed Circuit Board PCB ID: 1037593
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1. Digital System DesignDigital Design and Computer Architecture: ARM® EditionSarah L. Harris and David Money Harris
2. Digital System Design :: TopicsIntroductionComponent SelectionBill of Materials (BoM)Circuit ImplementationBreadboardingPrinted Circuit Board (PCB)Interpreting Datasheets
3. How to build a digital system?RequirementsComponent selectionImplementationDebugIntroduction
4. What is your purpose?Rapid prototyping / hackathon?Ease of design – breadboarding is great if possibleLow volume prototype / production?PCB, focus on features & schedule over costMass production?PCB, spend more time to drive down costContext Matters
5. FunctionPower ConsumptionForm FactorCostScheduleRequirements
6. Find parts to meet functionCapabilities / performanceSupply voltagePackageInterfacesPower consumptionEnvironmental qualification Temperature / vibration / radiation / etc.Geek out and follow components you likeArt of Electronicselectronicdesign.comComponent Selection
7. Pick parts with compatible logic levels5 V will cook most parts todayMany have 3.3 V interfacesSome only run at 1.8 V or lowerIf not possible, use level shiftersCore voltage may be lower than I/OMultiple power supplies requiredSupply Voltage
8. Through-holeConvenient for breadboardingConsumes lots of board areaUnavailable for modern partsSurface mount with pins on edgesGood choice for low volume PCBsSurface mount with pads underneathOnly option for some advanced componentsDifficult and costly to assemblePackage
9. Integrated Circuit Packagesdigikey.com
10. Through-hole componentsSMT Passive ComponentsPackage dimensions in mils0805 easiest for soldering0603 doable with skill0402 doable with much skill0201 for robots onlyOther packages
11. Some popular SMT components available on breakout boards. E.g. adafruit.com, sparkfun.comBreakout Boards
12. Internet of Things device 3.7 V 300 mA-h Li-ion rechargeable battery 20 mA in active mode (1% of the time) 0.1 mA in idle mode (99% of the time)Average power: 20 * 1% + 0.1 % 99% = 0.3 mABattery life: 300 mA-h / 0.3 mA = 100 hrs (6 weeks)Power Budget
13. Bill of Materials Example
14. SoftwareBoMLayer Stack & Trace WidthsSymbols & FootprintsSchematicLayoutRoutingDesign Rule ChecksFabricationAssemblyPCB Design
15. Software: Mentor Graphics PADSBoM: Components from DigiKey if possibleLayer Stack & Trace Widths2 layers for quick hacks4 layers for most Clinic prototypes6 mil minimum trace width + spacingFabrication: Advanced Circuits$33 / $66 student 2/4 layer specialsBeyond 5 units, standard pricing is betterAssembly: You or Action AssemblyPCB Design at HMC
16. Convert battery or wall wart to stable lower voltageRegulator typesDC regulators7805 drops >8 to exactly 5Low Dropout Regulators need less headroomSwitching regulatorsGreater efficiency (often > 80%)Require external inductorVoltage Regulators
17. All physical systems have inductance between the voltage regulator and circuits being poweredChanging current draw causes voltage drop across inductor, malfunctionsUse bypass capacitors to stabilize power supply10 μF near voltage regulator0.1 μF near each componentHigh-performance components need moreSee datasheet for guidancePower Supply Integrity
18. Learn standard terms for specsFully understand the datasheet before you use a componentSkimming is better than searchingInterpreting Datasheets
19. What is the power supply voltageHow much supply current does it draw?What are the logic levels?Can it read an input from 3.3V logic?How much output current could it drive?How to hook up an LED?How much input current does it draw?How to hook up to a switch?What packages are available?What temperature range can it operate over?Datasheet Examples: 74HC08
20. Cyclone II EP2C35F672From DE2 boardRepresentative FPGADatasheet Examples: Cyclone II
21. LIS3DHRepresentative peripheralSPI communicationDatasheet Examples: LIS3DH Accel
22. MicrocontrollerChallenge of big datasheetDatasheet Examples: STM32F042