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P14452: Detailed Design Review

This agenda outlines the topics to be covered in the detailed design review, including the review of updated specifications, mechanical design considerations, temperature and vibration solutions. Various analog and digital design elements will also be discussed.

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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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