Documentation/Hardware Selection

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This page intends to be a first sketch of the openmulticopter hardware. Feel free to contribute helpful ideas.

Contents

Microcontroller

ST Microelectronics Cortex M3: STM32F103xx (high-density controller)

  • 512 kB Flash
  • 64 kB RAM
  • 8 x 16 Bit Timer (IC, OC, PWM)
  • 2 x WDG
  • 3 x SPI
  • 2 x I2S
  • 2 x I2C
  • 5 x USART
  • 2 x UART
  • SDIO
  • USB
  • CAN

Package variants

Microcontroller Footprints ADC I/Os
STM32F103RE TQFP64, WLCSP64L 16 x 12 Bit 51
STM32F103VE TQFP100, LFBGA100 16 x 12 Bit 80
STM32F103ZE LQFP144, LFBGA144 21 x 12 Bit 112

Sensors

Gyroscopes

Gyroscopes are sensors that are used to measure angular velocity.

  • Melexis MLX90609
    • Supply voltage: 4.75 - 5.25 VDC
    • Supply current (no output load): 16 - 20 mA
    • Output not supply-ratiometric
    • Angular velocity range: +/- 300 °/s
    • Output voltage range: 0.5 - 4.5 VDC -> 4V
    • Nonlinearity: +/-0.5 % FSout
    • Zero rate output: 2.5 VDC
    • Zero rate temperature drift: +/- 5 % FSout (-40...+85°C)
    • Sensitivity: 6.67 mV/°/s
    • Sensitivity drift: +/- 5% S0 (-40...+85°C)
    • Spectral noise power density: 0.03 °/s/sqrt(Hz)
    • Angular rate cross-sensitivity for X, Y: 1 (typ) - 2 (max) % FSout
    • Resonance frequency: 8.2 kHz
    • Package: CLCC32, easy to solder by hand but large
    • Shock survival: +/- 1500g (0.5ms 3 axis)
    • Price
      • 36.30€ each in case of a purchase of > 3 units at Sander
      • 39.95$ each at Sparkfun
  • ADXRS610
    • Supply voltage: 4.75 - 5.25 VDC
    • Supply current (no output load): 3.5 - 4.5 mA
    • Output is supply-ratiometric
    • Angular velocity range: +/- 300 °/s
    • Output voltage range: rails at 0.25 and 4.75 V, respectively, range = 3.6V
    • Sensitivity: 6 mV/°/s
    • Spectral noise power density: 0.05 °/s/sqrt(Hz)
    • Resonance frequency: 12 - 17 kHz (14.5 kHz typ.)
    • Package: CBGA32, hot-air or reflow oven needed
    • Price
  • Ivensense IDG500
    • dual-axis
    • Supply voltage: 3 VDC
    • Supply current (no output load): 7 mA
    • Output is not supply-ratiometric
    • two different outputs for each axis (different range and sensitivity)
    • Angular velocity range: +/- 500 °/s and +/- 110 °/s
    • Sensitivity: 2 mV/°/s or 9.1 mV/°/s
    • RMS noise: 0.8 mV RMS in 1 Hz to 1kHz bandwidth range
    • Resonance frequency: 24kHz (X-axis) and 27kHz (Y-axis)
    • QFN 28 (4mm x 5mm x 1.2mm)
    • ISZ500 Z-axis complement (all three sensors can be mounted in PCB plane)
    • Price
  • ST LISY300AL
    • Supply voltage: 2.7 - 3.6 VDC
    • Supply current (no output load): 4.8 mA
    • supply-ratiometric?
    • Angular velocity range: +/- 300 °/s
    • Zero rate voltage at 1.65 V for 3.3 V supply
    • Sensitivity: 3.3 mV/°/s
    • Spectral noise power density: 0.1 °/s/sqrt(Hz)
    • Resonance frequency: 4.5 kHz
      • Low resonance frequency causes critical sensitivity to vibrations induced through the motors.
      • Even extended dampening measures might not eliminate this unwanted behaviour.
    • Price
  • ST LY530ALH + ST LPR530AL
    • Part of a new family of ST gyroscopes
    • Resonant frequency: 4100 Hz
  • Murata ENC-03A
    • Supply voltage: 3 VDC
    • SMD 8mm*4mm*3mm 0.2g easy to solder by hand
    • 6.7mV °/s
    • large temperature drift, compensation in software or with op-amp offset needed
    • low shock resistance
    • needs op-amp
    • price about 23.5 Euro

Acceleration Sensors

Used to get an attitude reference based on the effect of gravity in order to compensate for integral drift.

  • Analog Devices ADXL335
    • Replacement for the discontinued ADXL330
    • Analog output
    • 3 axis
    • Acceleration range: +/- 3g
    • Supply voltage range: 1.8 - 3.6 VDC
    • Supply current at 3V: 350uA
    • Sensitivity: 270 - 330 mV/g (300 mV/g typ.)
    • Sensitivity vs. temperature: +/- 0.01 %/°C
    • ...
    • Acceleration range: +/-5g
  • ST LIS3LV02DQ
    • Digital output (SPI, I2C)
  • ST LIS344ALH
    • Analog output
  • ...

Pressure Sensors

  • Freescale MP3H6115A
    • Supply voltage: 3 VDC
  • Freescale MPXH6115A6T1
    • Supply voltage: 5 VDC

Magnetic Sensors

  • 3 axis are required
  • PNI Micromag3
    • Supply voltage: 3.3 VDC
    • SPI
    • complete integrated 3 axis solution on a PCB
    • large but easy to mount
    • Price
    • 59€ at Sander
    • 59.95$ at Sparkfun
  • PNI MS2100
    • same as MM3 but as fully integrated one chip solution
    • only 2-axis, external third axis circuit can be interfaced to the chip
    • QFN-20
    • Price
  • Honeywell HMC1052L + HMC1051
    • 2 axis sensors HMC1052L + Z- axis HMC1051
  • Honeywell HMC5843
    • 3 axis sensor with i2c interface
    • 7 milli-gauss resolution
    • Breakout board 12.7x12.7mm
    • Price

Analog Circuitry, ADC

Voltage Level Adjustments

  • Gyroscopes usually operate at 5 VDC (Invensense and ST gyroscopes are 3.3V)
  • ACCs usually operate at 3.3 VDC
  • Depends on ADC input range

ADC

Considerations

  • Internal 12 Bit ADC
  • External ADC
    • Sensor noise limits ADC performance
    • Sample rate (10x oversampling required to reconstruct signal)
    • Interfacing to the MCU (fast SPI bus, simple protocol, conversion start through CS line)
    • Number of channels (3x gyros + 3x ACC + ...)
    • Small package variant, solderable by hand

External ADCs for Gyroscopes and ACCs

  • Maxim MAX1168
    • Resolution: 16 Bit
    • 8 channels
    • SPI interface
    • 5V analog supply voltage
    • 200 kSps max. (full time SPI transmission at max. clock rate, no breaks allowed)
  • Analog Devices AD7928
    • Resolution: 12 Bit
    • 8 channels
    • SPI interface
    • max. sample rate: 1 MSps

External ADCs for Pressure Sensor

  • LTC2440
    • SPI interface
  • LTC2485
    • I2C interface

Analog Sensor Filters

  • Bandwidth (depends on sample rate and closed control loop frequency)
  • Order of the filter
  • Active / passive filter
  • Number of parts, space needed on PCB
  • Filter type (e.g. Butterworth)

Interface

I2C

  • NXP PCA9306
    • I2C levelshifter / buffer
  • Analog ADUM1250
    • I2C Isolator

CAN

  • Microchip MCP2551
  • TI ISO1050
    • CAN Isolator (meets ISO11898 standard)

Power supply

  • 3 to 4 LiPo/ LiFePo cells: 9 to 16.8 VDC
  • Switching regulators
    • low power loss, high efficiency
    • switching noise
    • applications
      • probably a good solution for the main power supply
      • Step-up regulator for camera supply (12 VDC)
      • additional power supply for servos
    • examples:
      • TI PTH08080W
        • Supply current: 2.25 A
        • Input voltage range: 4.5 VDC - 18 VDC
        • Miniature power module, fully integrated solution, only few external components needed
  • Linear regulators
    • massive power dissipation in case of higher drop-out voltages
    • low noise
    • applications
      • post-switching-regulator solution (eg. 3.3 VDC main cpu supply)
      • low noise power supply for sensor circuitry
    • examples
      • Linear LT1763
        • very low noise
        • Supply current: 500 mA
        • Input voltage range: 1.8 VDC - 20 VDC
        • 300mV drop-out voltage
  • Servo Power Supply
  • Jumper to select between switching regulator provided supply and an external high current power supply in case of higher power demands.
  • Regular RC servo connectors

Temperature range

  • components should be chosen according to a specified voltage range
  • -40°C ... 85°C (flying on cold winter days must not cause any problems)

Assembling and Board Layouts

  • Size
    • 50 x 50 mm Mikrokopter + X-UFO compatible
    • 36 x 36 mm with 30mm* 30mm distance mounting holes booz HW, Booz_HB and IMU HB_autopilot compatible
    • all this IMUs PCB have SPI bus connection 16 bit ADCs, magnetic rate an accelerations sensors and have GPL license
    • other size, depending on actual space needs
  • Single/Multiple PCB(s)
    • 1x IMU (aka sensor board) + 1x MCU (main processor)
    • 1x IMU (gyroscopes + ACC) and MCU on a single board including pressure and magnetic sensors
    • 1x IMU (gyroscopes + ACC) and MCU on a single board + 1x NavBoard for pressure and magnetic sensors and GPS
    • ...
  • Additional PCBs
    • VDU / OSD
    • RC modem
    • RC receiver
    • ...
  • Number of Layers
    • 2 Layers
      • + easy and cheap manufacturing
      • + simple debugging (eg. green wire fixes)
      • - EMC considerations
      • - space requirements
    • 4 layers
      • + EMC suited layout
      • + higher density of parts possible -> smaller dimensions
      • - Cadsoft Eagle license necessary
      • - high priced manufacturing
      • - No debugging possible in case of flaws on inner layers.
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