P14452: Subsystems Design Review
ReviewWhere 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 AnalysisBuilding 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
• 180F
• Yield Strength
• 10400psi
• Modulus
• 450ksi
• CTE
• 278μin/in-°F
• Cost: 1.5”x6”x6” sheet
• $35.71
• Max Deformation
• .060”
• Max Stress
• ?
ANSYS Simulation
Polysulfone (PSU)
Properties• Max Operating Temp
• 285F
• Yield Strength
• 10900psi
• Modulus
• 390ksi
• CTE
• 29.4μin/in-°F
• Cost: 1.5”x6”x6” sheet
• $147.83
• Max Deformation
• .006”
• Max Stress
• 6862 psi
ANSYS Simulation
Polyester (Ertalyte® PET-P)
Properties• Max Operating Temp
• 210F
• Yield Strength
• 12400psi
• Modulus
• 490ksi
• CTE
• 33μin/in-°F
• Cost: 1.5”x6”x6” sheet
• $48.57
• Max Deformation
• .007”
• Max Stress
• 9744 psi
ANSYS Simulation
Aluminum 6061
Properties• Max Operating Temp
• 500F
• Yield Strength
• 40000psi
• Modulus
• 1000ksi
• CTE
• 13.1μin/in-°F
• Cost: 1.5”x6”x6” sheet
• $53.44
• Max Deformation
• .003”
• Max Stress
• ?
ANSYS Simulation
Weight
• Density:
• Acetal:
• .0513 lb/in3
• Polysulfone:
• .0448 lb/in3
• Polyester:
• .0361 lb/in3
• Aluminum:
• .0975 lb/in3
• Mass:
• Acetal:
• .0671 lb (30.4g)
• Polysulfone:
• .0586 lb (26.6g)
• Polyester:
• .0472 lb (21.4g)
• Aluminum:
• .1275 lb (57.8g)
Volume: 1.3075
in3
Other Properties
• Thermal Conductivity
• Acetal:
• 2.5 BTU-in/hr-ft²-°F
• Polysulfone:
• 3 BTU-in/hr-ft²-°F
• Polyester:
• 2 BTU-in/hr-ft²-°F
• Aluminum:
• 1160 BTU-in/hr-ft²-°F
• Electrical Resistivity
• Acetal:
• 1015 ohm-cm
• Polysulfone:
• 1016 ohm-cm
• Polyester:
• 1012 ohm-cm
• Aluminum:
• 10-6 ohm-cm
Pugh Analysis
Delrin PSU PET Al
Strength -
DATUM
+ +
Operating Temp - - +
Cost + + +
Weight s + -
Thermal Conductivit
ys s -
ElectricalResistivity s s -
Total 1/2 3/1 3/3
Case GeometryThe Best Things Come in Small Sizes
PCB DimensionsShow 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
MicrocontrollersChoosing 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)
• Floating Point
• DSP Instructions
• 1-3 Sigma-Delta ADC
• 16-bit
• 16.66 kHz max per channel
• DMA Interface
• ADC Synchronization
• 3 SPI (18 Mbit/s)
• Up to 84 GPIO
• 1 USB UART (12 Mbit/s)
MSP430F67XX• 16-bit RISC ( 8-25 MHz)
• No Floating Point
• No DSP Instructions
• 3 Sigma-Delta ADC
• 24-bit
• 31 kHz per channel max
• DMA Interface
• ADC Synchronization
• 2 SPI (5 Mbit/s)
• 52 or 72 GPIO
• No USB
Input ConditioningThe 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
• Simplified circuit
Final Circuit
Attenuator Non-ideality
10 100 1000 100000
1
2
3
4
5
6
7
8
f(x) = − 5.74854197E-09 x² + 0.00080073565 x + 0.000515302233
Percent Error vs Sensor Output Im-pedance
Series1
Sensor Ouput Impedance (Ohms)
Pe
rce
nt
of
Err
or
Power SourcePhenomenal 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/polymerli-ionbattery37v240mah602025.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
• Can get free samples
• TPS61200: 5 volt, 600mA boost converter
• 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 ItemsThe 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
• Small Device
• Large Device
• Finalize PCB Designs
• 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
• Sample Ordering
• Timestamp Calculation
• Processor Initialization Routines
Processes• Sampling Procedure
• Channel Switching
• Multiple Sampling Rate Switching
• DMA transfers
• Offload SPI
• Offload ADC
• Processor can focus on filtering and coordinating
Questions?El fin.
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