P14452: Subsystems Design Review. Review Where we left off

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)


• 285F

• Yield Strength

• 10900psi

• Modulus

• 390ksi

• CTE

• 29.4μin/in-°F


• $147.83

• Max Deformation

• .006”

• Max Stress

• 6862 psi

ANSYS Simulation

Polyester (Ertalyte® PET-P)


• 210F

• Yield Strength

• 12400psi

• Modulus

• 490ksi

• CTE

• 33μin/in-°F


• $48.57

• Max Deformation

• .007”

• Max Stress

• 9744 psi

ANSYS Simulation

Aluminum 6061


• 500F

• Yield Strength

• 40000psi

• Modulus

• 1000ksi

• CTE

• 13.1μin/in-°F


• $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:


• Aluminum:


• 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

http://www.all-battery.com/polymerli-ionbattery37v240mah602025.aspx

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.

Documents

P14452: Subsystems Design Review. Review Where we left off