P14452: Subsystems Design Review

ReviewWhere we left off

Updated Engineering Specifications

Previous Functional Decomposition

Capture Data

Store Data

Power Device

Protect Device

Chosen ConceptConcept # 4

Power Source UltraCapStart Capture Reed SwitchStop Capture Timer

Sensor Connection 4-WireSet Sampling Rate Digital Knob

Mount Device MagnetHigh Pressure Composite

High Temp Insulated/PassiveOily Env. Gaskets/Plugs

Data Storage microSDProcessor μC

Data Access USBSample 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 AnalysisDelri

n PSU PET Al

Strength -

DATUM

+ +Operating

Temp - - +

Cost + + +

Weight s + -Thermal

Conductivity

s 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 mV12 4096 4.88 mV14 16384 1.22 mV16 65536 305 uV18 262144 76.3 uV20 1048576 19.1 uV24 16777216 1.19 uV

Criteria 2: ADC TypeSuccessive 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 MB12 120k 51.498 MB 480k ~206 MB14 140k 60.081 MB 560k ~240 MB16 160k 68.885 MB 640k ~276 MB18 180k 77.248 MB 720k ~309 MB20 200k 85.831 MB 800k ~345 MB24 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

MicrocontrollersSTM32F373• 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 10000012345678

f(x) = − 5.74854197E-09 x² + 0.00080073565 x + 0.000515302233

Percent Error vs Sensor Output Im-pedance

Series1

Sensor Ouput Impedance (Ohms)

Perc

ent

of E

rror

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-ionbatte

ry37v240mah602025.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 ItemsMaterials 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.