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P14452: Detailed Design Review

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

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P14452: Detailed Design Review

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  1. P14452: Detailed Design Review

  2. 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)

  3. Review

  4. Updated Specifications

  5. Mechanical Design

  6. Temperature

  7. 3D Model Lid μC PCB Battery Case

  8. ANSYS Results Tamb = 55°C

  9. ANSYS Results Tamb = 95°C

  10. ANSYS Results

  11. Excel Model

  12. Excel Formulas

  13. Excel Results

  14. Excel Results

  15. Excel Results

  16. Vibration

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

  18. 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

  19. Where C = Modal constant E = 2.7e6 b = 30mm =1.18 inches h =1/8 inch I = bh3/12 = 0.000192 g = 386 in./s2 p = 1850 kg/m³ = .0668 lb/in3 L = 35mm = 1.378 inches W = pbhL= 0.0136 lb w = W/L = .00985 lb/in.

  20. Solutions

  21. Aluminum Case • Aluminum Case for Harsh Environment • Watertight • Integrated Standoff • No Integrated Flange Mount Hammond Mfg. 1590Z Series Various Sizes Available

  22. Plastic Case • Lightweight Plastic Case • Integrated Flange Mount • Integrated PCB Standoff • Black or Grey!! Hammond Mfg. 1551 FL Series Various Sizes Available

  23. Test Plan

  24. Analog Design Sensing the World

  25. 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

  26. First order LPF • Circuit above is a inverting op-amp with a RC 1st Order LPF

  27. 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

  28. MAX7403 Interfacing • I2C interfacing • Set the cutoff frequency in software to accommodate other sampling rates • 8 pin package • About 1mV offset at 85C

  29. 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

  30. Example Compatible Sensors ADXL203 AC2626 2 –axis Accelerometer +/- 1.7, 5 , 15 g range 2.5 kHz bandwidth 0 – 5V range 0.5 C Accurate Temperature Sensor -55 C – 150 C 0 – Vs Voltage Range

  31. LiPo Charging • Spark Fun Power Cell – LiPo Charger/Booster • Micro USB charging • $19.99 breakout board for testing • Eagle Files Available for PCB layout

  32. Schematic for LiPo Charging and Booster https://www.sparkfun.com/products/11231

  33. 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

  34. 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)

  35. Digital Design As easy as 0xABC123

  36. Microcontroller Selection

  37. 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)

  38. 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

  39. Software Processes

  40. Modes of Operation • Charging • Not Sampling • Peripherals Disabled • Delay • Not Sampling • Peripherals Initialized • Timer Running • Normal • Sampling • Timer Running

  41. Main Program Execution

  42. Peripheral Initialization

  43. Sampling Process (ADC Subroutine)

  44. Write Process (SPI Subroutine)

  45. Moving Forward The long road to graduation

  46. BOM – Small Design

  47. BOM - Large Design

  48. Budget Allocation

  49. Risk Assessment

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