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P14452: Subsystems Design Review Review Where we left off Updated Engineering Specifications Previous Functional Decomposition Capture Data Store Data Power Device Protect Device Chosen Concept Concept # 4 Power Source UltraCap Start Capture Reed Switch Stop Capture Timer Sensor Connection 4-Wire Set Sampling Rate Digital Knob Mount Device Magnet High Pressure Composite High Temp Insulated/Passive Oily Env. Gaskets/Plugs Data Storage microSD Processor μC Data Access USB Sample Bit Width 16-bit Sample Rate 10kHz Materials Analysis Building a Better Box Plan • • Comparisons of Materials • • • • Acetal Resin (Delrin®-150) Polysulfone Polyester (Ertalyte® PET-P) Aluminum 6061 Applied Loads • • 100psig applied to external surfaces 200F applied to bodies Acetal Resin (Delrin®-150) Properties • Max Operating Temp • • Yield Strength • • $35.71 Max Deformation • • 278μin/in-°F Cost: 1.5”x6”x6” sheet • • 450ksi CTE • • 10400psi Modulus • • 180F .060” Max Stress • ? ANSYS Simulation Polysulfone (PSU) Properties • Max Operating Temp • • Yield Strength • • $147.83 Max Deformation • • 29.4μin/in-°F Cost: 1.5”x6”x6” sheet • • 390ksi CTE • • 10900psi Modulus • • 285F .006” Max Stress • 6862 psi ANSYS Simulation Polyester (Ertalyte® PET-P) Properties • Max Operating Temp • • Yield Strength • • $48.57 Max Deformation • • 33μin/in-°F Cost: 1.5”x6”x6” sheet • • 490ksi CTE • • 12400psi Modulus • • 210F .007” Max Stress • 9744 psi ANSYS Simulation Aluminum 6061 Properties • Max Operating Temp • • Yield Strength • • $53.44 Max Deformation • • 13.1μin/in-°F Cost: 1.5”x6”x6” sheet • • 1000ksi CTE • • 40000psi Modulus • • 500F .003” Max Stress • ? ANSYS Simulation Weight • • Density: • • Polyester: • • .0448 lb/in3 • • Volume: 1.3075 in3 • .0975 lb/in3 .0586 lb (26.6g) Polyester: • • .0671 lb (30.4g) Polysulfone: • .0361 lb/in3 Aluminum: Acetal: • .0513 lb/in3 Polysulfone: • • • Acetal: • Mass: .0472 lb (21.4g) Aluminum: • .1275 lb (57.8g) Other Properties • Thermal Conductivity • Acetal: • • • • 1160 BTU-in/hr-ft²-°F Acetal: • • • 1016 ohm-cm Polyester: • • 1015 ohm-cm Polysulfone: • 2 BTU-in/hr-ft²-°F Aluminum: • • 3 BTU-in/hr-ft²-°F Polyester: • Electrical Resistivity 2.5 BTU-in/hr-ft²-°F Polysulfone: • • 1012 ohm-cm Aluminum: • 10-6 ohm-cm Pugh Analysis Delrin PSU PET Al Strength - + + Operating Temp - - + Cost + + + Weight s + - Thermal Conductivity s s - Electrical Resistivity s s - Total 1/2 3/1 3/3 D A T U M Case Geometry The Best Things Come in Small Sizes PCB Dimensions Show 3D Rendering Mounting • Two part solution • Flange Base • • • Through Hole in each corner Can be used to mount directly Adapter Plates • • • Attach to flange base Allow for Mounting on existing holes Allow for adhesive, zelcro, magnets, etc. Generalized Design • Rectangular Prism • • 1-3 Ports for Analog I/O 1 Micro-USB Port • • • Charging Data Access Flange Base • Fasten from Bottom • • Locks access to inside of device when mounted Provides Mounting Holes Microcontrollers Choosing a Better Brain Criteria 1: ADC Accuracy Bit Width # of Values LSB (Accuracy) 10 1024 19.53 mV 12 4096 4.88 mV 14 16384 1.22 mV 16 65536 305 uV 18 262144 76.3 uV 20 1048576 19.1 uV 24 16777216 1.19 uV Criteria 2: ADC Type Successive Approximation • • • 10-12 bit Accuracy Fast Sample Rate (>200kS/s) Requires External Low-pass Filter • Costs Board Space • • 3 Op-amps (Bi-Quad) Resistors and capacitors Sigma-Delta • • • 12-24 bit Accuracy Slow Sample Rate (<200kS/s) No External Low-pass Filter • Filter is part of sampling process • Must be careful of bit width effect on frequency range Criteria 3: Serial Throughput (SD) Bit Width Bits/s (1 Ch)* Bytes/hr (1 Ch)* Bits/s (4 Ch)* Bytes/hr (4 Ch)* 10 100k 42.915 MB 400k ~172 MB 12 120k 51.498 MB 480k ~206 MB 14 140k 60.081 MB 560k ~240 MB 16 160k 68.885 MB 640k ~276 MB 18 180k 77.248 MB 720k ~309 MB 20 200k 85.831 MB 800k ~345 MB 24 240k 102.997 MB 960k ~412 MB * at 10kHz sampling rate Criteria 4: I/O Capability • • • • SD Card • • 1 SPI interface 1 Serial Clock USB Data Access • 1 USB UART ADC • 1-4 ADC Channels GPIO • • 1 Digital (SD) >2 Digital for Hardware Sampling Rate (per channel) Criteria 5: Processor Speed • ADC requirement • 10000 Samples/s per Channel • • May take more than 1 cycle per sample to read from ADC Estimated Minimum Speed • • • 40000 Samples/s (4 Channels) 2 Cycles per Sample Read 112 Cycles per Sample Write • • • • • • 5 Bytes Data 1 Bytes Channel ID 5 Bytes Timestamp 2 Bytes “,” 1 Byte CR 4.56 MHz Microcontrollers STM32F373 • 32-bit ARM M4F (72 MHz) • • • • • • • DSP Instructions • 16.66 kHz max per channel DMA Interface ADC Synchronization Up to 84 GPIO 1 USB UART (12 Mbit/s) • • • No Floating Point No DSP Instructions 3 Sigma-Delta ADC • • • • 16-bit 3 SPI (18 Mbit/s) 16-bit RISC ( 8-25 MHz) • • Floating Point 1-3 Sigma-Delta ADC • • • • MSP430F67XX 24-bit 31 kHz per channel max DMA Interface ADC Synchronization 2 SPI (5 Mbit/s) 52 or 72 GPIO No USB Input Conditioning The Large Signal Problem Attenuation Circuit • Use resistor bridge to reduce the voltage for input to microcontroller • Set a unity gain • Also decreases the current going into the uC • Simplified circuit 𝑅3 ∗𝑅𝐿 • 𝑅𝐵 = 𝑅2 + 𝑅3+𝑅𝐿 • 𝑉𝐵 = 𝑉𝐿 Simplified Circuit 𝑅3 𝑅3 𝑅𝐿 • 𝑉𝐵 = 𝑅1 𝑅𝐵 𝑉𝑠 𝑅1 𝑅𝐵 +𝑅𝐿 •𝐺= 𝑉𝐿 𝑉𝑆 1+𝑅 𝑠 1 𝑅3 𝑅2 +𝑅𝐿 𝑅3 +𝑅𝐿 1 𝑅 2+ 3 𝑅𝐿 Final Circuit Attenuator Non-ideality Percent Error vs Sensor Output Impedance 8 y = -6E-09x2 + 0.0008x + 0.0005 Percent of Error 7 6 5 4 Series1 3 Poly. (Series1) 2 1 0 1 10 100 1000 Sensor Ouput Impedance (Ohms) 10000 Power Source Phenomenal Cosmic Power. Itty Bitty Living Space. LiPo vs. Ultra Capacitor Ultra Capacitor (KEMET FT0H105ZF) • Diameter = 21.5mm (0.846in) • Height = 13mm(0.512in) • Area= 1502mm^3 • Max Voltage 5.5V • 1F capacitance • Max current is 1.5mA for 30 mins • Weight = 10 grams • Price 1$4.23, 10$38.03 • KEMET FT Series pages 2-4 LiPo Battery (All-battery.com 602025) • Base: 25mm x 20mm • Height: 6mm • Area=3000mm^3 • Voltage = 3.7V • 240 mAh • Max Current is 48mA for 5 Hours • Weight = 4 grams • Price for 5-10$3.25 each • http://www.all-battery.com/polymerliionbattery37v240mah602025.aspx LiPo Charging • Spark Fun Power Cell – LiPo Charger/Booster • Micro USB charging • $19.99 breakout board for testing • Eagle Files Available for PCB layout Schematic for LiPo Charging and Booster https://www.sparkfun.com/products/11231 • Components Required LiPo Charger and Booster MCP73831/2: LiPo Charging IC • • TPS61200: 5 volt, 600mA boost converter • • • • • Can get free samples Can get free samples Used for powering sensors and other components JST connector $0.95 Micro USB SMD Connector $1.95 Resistors and Capacitors <$2.00 Action Items The Road Ahead Mechanical Action Items Materials and Modelling • • Choose Final Material Solid Modelling • • • Small Device Large Device Ansys Simulations • • Small Device Large Device Sensor Characterization • Catalog Existing Sensors in Compressor • • Centralized Collection of Data Sheets Reference Card for Sensors • • • • • Voltage Range Current Output Frequency Ranges Optimal Sampling Rate Voltage to Unit Conversion Factor Electrical Action Items PCB • Finalize Electrical Schematics • • • Large Device Finalize PCB Designs • • • Small Device Small Device Large Device Final Component Selection Analog Analysis • • • • Attenuator Final Design Differential Amplifier Precision Voltage Reference Input Voltage Clamping • • Overvoltage Protection LiPo Charging Circuitry Computer Action Items Algorithms • • • • Digital Filtering Processes • • • Sample Ordering Timestamp Calculation Processor Initialization Routines Sampling Procedure • Channel Switching Multiple Sampling Rate Switching DMA transfers • • • Offload SPI Offload ADC Processor can focus on filtering and coordinating Questions? El fin.