P14452: Detailed Design

Review

Agenda

• Review (10 mins)• Updated Specifications

• Mechanical Design (30 minutes)• Temperature• Vibration• Solutions

• Analog Design (20 minutes)• Analog Signal Conditioning• Example Sensors• Power

• Digital Design (10 minutes)• Microprocessor Selection• Software Processes

• Moving Forward (10 minutes)

• Questions (10 minutes)

Review

Updated Specifications

Mechanical Design

Temperature

μC

Battery

Lid

Case

PCB

3D Model

Tamb = 55°C

ANSYS Results

Tamb = 95°C

ANSYS Results

ANSYS Results

Excel Model

Excel Formulas

Excel Results

Excel Results

Excel Results

Vibration

“Most component failures in a severe vibration environment will be due to cracked solder joints, cracked seals, or broken electrical lead wires.”

Vibration-related Failure

• Cause:• Due to stresses from relative

motion between component body, electrical lead wires, and the PCB

• Solutions:• Tying or cementing

component to PCB to eliminate resonance

• Proper component placement on rectangular PCB

• Attributes• Most severe during resonant

conditions• Can develop when component

body acts as mass and lead wires act as springs

• Most severe conditions at center of PCB

• On rectangular PCB, most severe conditions are when component part is parallel to short side of board

𝑓 𝑛=𝐶 √ 𝐸𝐼𝑔𝑤 𝐿4

Where C = Modal constant

E = 2.7e6b = 30mm =1.18 inchesh =1/8 inchI = bh3/12 = 0.000192g = 386 in./s2

p = 1850 kg/m³ = .0668 lb/in3

L = 35mm = 1.378 inchesW = pbhL = 0.0136 lbw = W/L = .00985 lb/in.

𝑓 𝑛=3.56√ (2.7∗106 )∗ .000192∗386.00985∗1.3784

𝑓 𝑛=8450Hz

Solutions

Aluminum Case

• Aluminum Case for Harsh Environment• Watertight• Integrated Standoff

•No Integrated Flange Mount

Hammond Mfg.1590Z SeriesVarious Sizes Available

Plastic Case

• Lightweight Plastic Case• Integrated Flange Mount• Integrated PCB Standoff• Black or Grey!!

Hammond Mfg.1551 FL SeriesVarious Sizes Available

Test Plan

Eng Spec

Name Measure Method InstrumentPassing Criteria

ES1 Easily Mountable Process -

ES14 Mountable on Moving Part Possible -

ES2 Small Size Volume Measure Volume Ruler Small (≈1in3)

ES13 Harsh EnvironmentPassing of Sub-specifications

 

ES13.1 High Temperature TempRaise ambient

TempTest at CIMS

Reaches 140F

ES13.2 High Pressure Pressure Raise ambient PresTest at CIMS

Reaches 100psi

ES13.3 Oily Environment Possible Submerge in oil Oil tank Withstands oil

ES13.4 Withstand Vibration Acceleration Raise Vibration Vibe table Reaches 5G

ES3 Set Sampling Rate in Field Present -ES4 No External Wires Not Present -ES5 Universal Sensor Connector Present -ES7 Data Storage Capacity (Time) Store Data Computer Stores 60 min

ES7.1 Start Capture Present -

ES7.2 Stop Capture Present -

ES6 Types of Sensor # of Different Sensors -ES8 Power To Sensors Voltage      

ES9Multiple Sampling Frequencies

Frequency      

ES10 Timestamps Accuracy      ES11 High Sampling Frequency Max Sampling Frequency Measure Max Freq   20kHzES12 Digital Bit Width (Accuracy) Bits per Sample Max Accuracy   12bit

ES12.1 Voltage Accuracy ADC LSB      ES15 Multiple Sensors Maximum Sensors -

ES16 Sensor Voltage Range Voltage      

Analog Design

Sensing the World

Low-pass Filter

• Passes low frequency signals and attenuates signals with higher frequencies than the cutoff

• Used for smoothing data

• Reduces noise

• Necessary for SAR style ADC

First order LPF

• Circuit above is a inverting op-amp with a RC 1st Order LPF

MAX7403 8th Order LPF

• 8th order Low-pass Elliptic Filter

• 8 times faster cutoff than 1st order LPF

• Lower Band Reject frequency• Lower ADC sampling

rate

• Eliminates the need for discrete resistors in the Analog Signal Path

• Maxim EE-SIM

MAX7403 Interfacing

• I2C interfacing

• Set the cutoff frequency in software to accommodate other sampling rates

• 8 pin package

• About 1mV offset at 85C

Maxim DS4420

• Programmable gain amplifier

• -35dB-40dB Range

• -11 dB attenuation on 0-10V range yields 0-2.818 signal• 2.88 mV accuracy with 12

bit ADC

• Up to 8 devices on the same I2C bus

Example Compatible Sensors

ADXL203• 2 –axis Accelerometer

• +/- 1.7, 5 , 15 g range

• 2.5 kHz bandwidth

• 0 – 5V range

AC2626• 0.5 C Accurate Temperature

Sensor

• -55 C – 150 C

• 0 – Vs Voltage Range

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, 1.2A 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

Li-Po Temperature Issues

• Prof. Landi, Chemical Engineering, said that he does not know of any technologies that can operate up to 200F

• Battery’s composition layers begin to breakdown at max temperature

• Risk explosion if operating over the indicated max operating temperature (60C)

Digital Design

As easy as 0xABC123

Microcontroller Selection

Necessary Features

• ADC• 1-4 Channels• 12-bit Accuracy• 25 kHz Sampling Rate per

channel

• Digital• 1 SPI (SD)• 1 I2C (Attenuator Config)• 1 PWM (LPF Config)• 2 GPIO (Power Monitoring)

Freescale KL05

• 3 x 3 mm footprint

• 48 MHz

• ADC• 12-bit• 12 Channels• ~800 kS/s Max

• SPI

• I2C

• PWM (6 Ch + 2 Ch)

• ~$2 ea.

• $13 FRDM-KL05Z Dev Board

Software Processes

Modes of Operation

• Charging• Not Sampling• Peripherals Disabled

• Delay• Not Sampling• Peripherals Initialized• Timer Running

• Normal• Sampling• Timer Running

Main Program Execution

Peripheral Initialization

Sampling Process (ADC Subroutine)

Write Process (SPI Subroutine)

Moving Forward

The long road to graduation

BOM – Small Design

Component Price Quantity TotalPlastic Case $5 4 $20.00 MKL05Z32VFK4 (uC) $1.91 4 $7.64 DS4420N+ (Attenuator) $3.69 4 $14.76 MAX7403CSA+ (Low Pass Filter) $7.09 4 $28.36 MCP73831 (LiPo Charger) $0.64 4 $2.56 TPS61200DRCR (Boost Converter) $2.43 4 $9.72 LiPo 3.7 240 mAh $3.39 4 $13.56 CDRH2D18 (Inductor) $0.81 4 $3.24 DX4R005HJ5R2000 (Micro USB) $0.89 4 $3.56 SCHA5B0200 (microSD Socket) $1.48 4 $5.92 2 - layer PCB $83.70 1 $83.70 MISC $25.00

Total $218.02

BOM - Large Design

Component Price Quantity TotalPlastic Case $5 4 $20.00 MKL05Z32VFK4 (uC) $1.91 4 $7.64 DS4420N+ (Attenuator) $3.69 16 $59.04 MAX7403CSA+ (Low Pass Filter) $7.09 16 $113.44 MCP73831 (LiPo Charger) $0.64 4 $2.56 TPS61200DRCR (Boost Converter) $2.43 4 $9.72 LiPo 3.7 450 mAh $4.00 4 $16.00 CDRH2D18 (Inductor) $0.81 4 $3.24 DX4R005HJ5R2000 (Micro USB) $0.89 4 $3.56 SCHA5B0200 (microSD Socket) $1.48 4 $5.92 2 - layer PCB $87.20 1 $87.20 MISC $50.00

Total $378.32

Budget Allocation

Component Cost

Small Design $218.02

Large Design $378.32

Programmer Cable $120

Dev Board $13

Total $729.34

Risk Assessment

ID Risk Effect CauseLikelihood

Severity

Priority Preventative Action

Person(s) Rsponsible

R1

Casing Rupture Total System Failure Material Failure 1 5 5

Prevent by selecting quality casing material and seals

Chris/Dennis

R2 Storage Full Data LossInadequate Storage 2 5 10 Capacity Theory and Testing Bryan

R3

Poor Timestamp Accuracy Unreliable Data

Poorly written code 2 4 8

Comparison of results with Lab DAQ Bryan

R4

PCB Manufacturing Latency

Delays in Implementation and Testing

Poor PCB Design or Assembly 2 5 10

Designs will be verified by third-party Matt

R5

Battery Overheats

Device Loses Power/Battery Explodes Temp too high 2 5 10 Reduce Operating Temp Dennis

R6

Electronics get too hot Innacurate Data Temp too high 2 4 8

Reduce Operating Temp, Temp Compensating Filters Dennis/Matt

R7

Internal Damage to PCB Vibration too high Poor dampening 1 4 4

Have proper vibration dampening for system Chris

Schedule (Break)

Week 1 2 3 4 5 6

Phase 0

Matt PCB Design and Order

Chris Determine Suitable Compressor Mounting Locations

Dennis Research PCB Electrical Isolation and Heat Sinking Techniques

Bryan Microcontroller Initialization

Schedule (MSD II)

Week 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Phase 1 2 3 4 5

Matt PCB Assembly PCB Functionality TestingPCB

PerformanceTesting

TechnicalPaper

Chris MountingSolutions

Design / Build VibrationTest Rig

PCB Vibration Testing

Dennis Case Modification and Preparation PCB Integration

Bryan Write Basic Firmware Test Firmware Additional Functionality

Questions?

El fin.