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Audible altimeter part 2

Below is notes about the components chosen for the first version of the altimeter and some notes.

  • Air pressure changes approximately 1.44kPa / 100m
  • Sensor interface: i2c
    • SPI would be easier to interface with, but I2C is better learning experience
    • The USB library I’m planning on using has also I2C module (1)
  • MCU: atxmega128a4u
    • 1.6V-3.6V
    • max 32MHZ @ 2.7V
    • max 12MHZ @ 1.6V
    • max 12mA @ 32MHZ @ 3.0V + 0.5mA from 32MHz internal OSC
    • I/O max 20mA per pin
    • 4.5€ @ Digikey
  • Barometer: Freescale: MPL3115A2 (2)
    • Pressure, temperature and altitude
    • 20bit
    • 50kPa – 110kPa (= >4000m – 0m)
    • 0.3m resolution
    • 0.1kPa relative accuracy (changing temperature)
    • Probably not very good for this purpose, but is cheap (2.5€) and gets the project started
    • 6ms-512ms / sample
    • 8.5µA-40µA-265µA@3.3V 1Hz update rate
    • I2C
    • 2.9€ @ Digikey
    • 2V – 3.6V
  • Barometer2: Measurement Specialties: MS5805-02BA01
    • 1.8V – 3.6V
  • Acceleration/heading: InvenSense MPU-9250 (3)
    • Just for the fun of it
    • Barometer data might be little bit boring while developing
    • 5mA max?
    • I2C
    • 11€
    • 2.4V – 3.6V
  • GPS: Linx FM Module
    • http://www.linxtechnologies.com/resources/data-guides/rxm-gps-fm.pdf
    • 3.0V – 4.3V
  • GPS: SIM33ELA ?
  • GPS antenna: Pulse W3011A
  • Hymidity sensor: Silicon Labs 336-2540-1-ND
    • I2C
    • 1.9V – 3.6V
  • Clock: Microchip MCP7940M (4)
    • MCU could do everything this chip can do, but why not just add another i2c chip?
    • 1.2µA@3.3V timekeeping
    • 0.69€ @ Digikey MCP7940MT-I/MNY MCP7940MT-I/MNYCT-ND
    • I2C
    • 1.8V – 5.5V
  • Crystal Oscillator
    • 0805
    • 0.9€ @ Digikey CM315D32768EZFT 300-8816-1-ND
    • +-20ppm
  • Display: LS013B4DN04 / LS013B7DH03
    • 32mm x 28mm x ~1.5mm
    • 2.7V – 3.3V
    • 12µW dynamic display @ 1Hz
    • 15€ (Mouser)
  • FPS connector
    • SFV10R-2STE1HLF 609-4306-1-ND – Top contacts
    • SFV10R-1STE1HLF 609-4305-1-ND – Bottom contacts <- Use this for 180 bent (under PCB)
    • 0.55€ (Digikey)
    • 0.5mm pitch
    • 0.3mm FPC thickness
    • 0.7€ @ Digikey
  • Buzzer
    • CSS-0575A-SMT-TR 102-2201-1-ND
    • 3.7€ (Digikey)
    • 5mm x 5mm x 2.4mm
    • Drive with NPN BJT + 180 OHM + protective diode
    • 3.2€ @ Digikey
    • 2V – 4V
  • USB charging IC
    • MCP73831 http://www.digikey.fi/product-detail/en/MCP73831T-2ACI%2FOT/MCP73831T-2ACI%2FOTCT-ND/1979802
    • Sparkfun
    • 0.4€ @ Digikey
  • USB connector
    • Micro B
    • 0.4€ @ Digikey 609-4616-1-ND or 609-4618-1-ND
  • Micro SD card slot
    • 1.1€ @ Digikey 101-00660-68-6-1-ND
  • Flash memory
    • S25FL216K
    • 2.7V – 3.6V
    • SOIC-8
  • 3.3V supply IC
    • Linear regulator
    • Reasoning: For 3.3V linear offers ~90% efficiency. 2.7V design would not benefit much more. Switching regulator would require board space and add complexity. Maybe next time.
    • Reasonable transient characteristics? (AND9089-D)
    • 0.7€ @ Digikey NCP4681DSQ33T1G NCP4681DSQ33T1GOSTR-ND
  • 400mAh battery: 403035
    • 35mm x 30mm x 4mm
    • 7€ (ebay)
    • 3.7V
    • 2.7V – 4.5V
  • Current consumption active:
    • 13mA: MCU
    • 0.3mA: Barometer
    • 5mA: 9Axis
    • 0.001mA: Clock
    • 0.015mA: Display
    • <= 20mA (buzzer not included)
    • = 20h @ 400mAh
  • Current consumption waiting:
    • 1mA: MCU (MAX) (active 1MHz)
    • 0.01mA: Barometer
    • 0.015mA: Display
    • <= 2mA
    • >= 1 week
  • For 9 month battery life
    • 400mAh / 24309h = 62µA
    • 5µA: MCU (32kHZ)
    • ~1µA LDO
    • 1.2µA: Clock
    • = Should be possible

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