Transcript display

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
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Comparisons of Materials
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Acetal Resin (Delrin®-150)
Polysulfone
Polyester (Ertalyte® PET-P)
Aluminum 6061
Applied Loads
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100psig applied to external surfaces
200F applied to bodies
Acetal Resin (Delrin®-150)
Properties
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Max Operating Temp
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Yield Strength
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$35.71
Max Deformation
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278μin/in-°F
Cost: 1.5”x6”x6” sheet
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450ksi
CTE
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10400psi
Modulus
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180F
.060”
Max Stress
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?
ANSYS Simulation
Polysulfone (PSU)
Properties
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Max Operating Temp
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Yield Strength
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$147.83
Max Deformation
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29.4μin/in-°F
Cost: 1.5”x6”x6” sheet
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390ksi
CTE
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10900psi
Modulus
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285F
.006”
Max Stress
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6862 psi
ANSYS Simulation
Polyester (Ertalyte® PET-P)
Properties
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Max Operating Temp
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Yield Strength
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$48.57
Max Deformation
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33μin/in-°F
Cost: 1.5”x6”x6” sheet
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490ksi
CTE
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12400psi
Modulus
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210F
.007”
Max Stress
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9744 psi
ANSYS Simulation
Aluminum 6061
Properties
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Max Operating Temp
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Yield Strength
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$53.44
Max Deformation
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13.1μin/in-°F
Cost: 1.5”x6”x6” sheet
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1000ksi
CTE
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40000psi
Modulus
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500F
.003”
Max Stress
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?
ANSYS Simulation
Weight
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Density:
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Polyester:
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.0448 lb/in3
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Volume:
1.3075 in3
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.0975 lb/in3
.0586 lb (26.6g)
Polyester:
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.0671 lb (30.4g)
Polysulfone:
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.0361 lb/in3
Aluminum:
Acetal:
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.0513 lb/in3
Polysulfone:
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Acetal:
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Mass:
.0472 lb (21.4g)
Aluminum:
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.1275 lb (57.8g)
Other Properties
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Thermal Conductivity
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Acetal:
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1160 BTU-in/hr-ft²-°F
Acetal:
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1016 ohm-cm
Polyester:
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1015 ohm-cm
Polysulfone:
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2 BTU-in/hr-ft²-°F
Aluminum:
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3 BTU-in/hr-ft²-°F
Polyester:
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Electrical Resistivity
2.5 BTU-in/hr-ft²-°F
Polysulfone:
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1012 ohm-cm
Aluminum:
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10-6 ohm-cm
Pugh Analysis
Delrin
PSU
PET
Al
Strength
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Operating
Temp
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Cost
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Weight
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Thermal
Conductivity
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s
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Electrical
Resistivity
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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
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Two part solution
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Flange Base
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Through Hole in each corner
Can be used to mount directly
Adapter Plates
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Attach to flange base
Allow for Mounting on existing holes
Allow for adhesive, zelcro, magnets, etc.
Generalized Design
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Rectangular Prism
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1-3 Ports for Analog I/O
1 Micro-USB Port
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Charging
Data Access
Flange Base
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Fasten from Bottom
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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
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10-12 bit Accuracy
Fast Sample Rate (>200kS/s)
Requires External Low-pass Filter
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Costs Board Space
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3 Op-amps (Bi-Quad)
Resistors and capacitors
Sigma-Delta
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12-24 bit Accuracy
Slow Sample Rate (<200kS/s)
No External Low-pass Filter
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Filter is part of sampling process
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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
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SD Card
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1 SPI interface
1 Serial Clock
USB Data Access
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1 USB UART
ADC
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1-4 ADC Channels
GPIO
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1 Digital (SD)
>2 Digital for Hardware Sampling Rate (per channel)
Criteria 5: Processor Speed
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ADC requirement
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10000 Samples/s per Channel
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May take more than 1 cycle per sample to read from
ADC
Estimated Minimum Speed
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40000 Samples/s (4 Channels)
2 Cycles per Sample Read
112 Cycles per Sample Write
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5 Bytes Data
1 Bytes Channel ID
5 Bytes Timestamp
2 Bytes “,”
1 Byte CR
4.56 MHz
Microcontrollers
STM32F373
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32-bit ARM M4F (72 MHz)
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DSP Instructions
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16.66 kHz max per channel
DMA Interface
ADC Synchronization
Up to 84 GPIO
1 USB UART (12 Mbit/s)
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No Floating Point
No DSP Instructions
3 Sigma-Delta ADC
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16-bit
3 SPI (18 Mbit/s)
16-bit RISC ( 8-25 MHz)
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Floating Point
1-3 Sigma-Delta ADC
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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
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Components Required LiPo Charger and
Booster
MCP73831/2: LiPo Charging IC
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TPS61200: 5 volt, 600mA
boost converter
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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
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Choose Final Material
Solid Modelling
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Small Device
Large Device
Ansys Simulations
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Small Device
Large Device
Sensor Characterization
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Catalog Existing Sensors in Compressor
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Centralized Collection of Data Sheets
Reference Card for Sensors
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Voltage Range
Current Output
Frequency Ranges
Optimal Sampling Rate
Voltage to Unit Conversion Factor
Electrical Action Items
PCB
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Finalize Electrical Schematics
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Large Device
Finalize PCB Designs
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Small Device
Small Device
Large Device
Final Component Selection
Analog Analysis
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Attenuator Final Design
Differential Amplifier
Precision Voltage Reference
Input Voltage Clamping
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Overvoltage Protection
LiPo Charging Circuitry
Computer Action Items
Algorithms
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Digital Filtering
Processes
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Sample Ordering
Timestamp Calculation
Processor Initialization Routines
Sampling Procedure
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Channel Switching
Multiple Sampling Rate Switching
DMA transfers
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Offload SPI
Offload ADC
Processor can focus on filtering and coordinating
Questions?
El fin.