wiki/ avionics/ av3-imu
  1. Welcome to the AV3 IMU page
    1. Theo IMU Board Design
      1. Component list
        1. Accelerometers:
        2. Gyroscope:
        3. Magnetometer:
      2. GFE <-> Sensors pin out
      3. Software
        1. Input (needs work):
        2. Output
      4. Signal Processing
    2. ADIS IMU
      1. Hardware
      2. Pin Connections GFE <-> ADIS
      3. Software

Welcome to the AV3 IMU page

The AV3 IMU is in the early design phase. Several years have passed since the last IMU design, hence it is prudent to preform a new component survey. The top criteria are accuracy, price, and bandwidth. The last exploration into the accelerometer/gyroscope market reviled a decidedly bimodal distribution. Either components were very accurate and very expensive (beyond the means of PSAS) or inexpensive and low accuracy. The specifications for the accelerometers listed on sensorportal.com are being summered on the google docs spread sheet. This summary should be complete by mid June. Data sheets will be posted as soon as I can figure out how to attach files to this wiki.

Theo IMU Board Design

Component list

Accelerometers:

Gyroscope:

Magnetometer:

All these sensors have digital output, which is a good thing because it simplifies the design and lowers cost but the trade off is a somewhat higher noise floor, slower sampling rates and less resolution. The selected sensors should perform well enough for our use on the rocket. I also get the feeling that a bunch of other cheap digital output sensors will be appearing in the next year or so, so we should keep our eyes open.

Something to note is that none of the sensors have similar sensor rates. This probably makes using the data difficult?

GFE <-> Sensors pin out

Software

The IMU receives single character commands over bulk USB transfers and outputs sensor data on bulk.

Input (needs work):

Output

Outputs sensor data in packets formatted like this:

| Sensor ID | Time Stamp | Status | X | Y | Z | Additional Data |

Data is sent as soon as the IMU gets it from a sensor, the maximum sample rate on the fastest sensor is 1kHz and the data packet can be repeated in a USB packet if there's more than one to send at the same time.

Signal Processing

Done host side?

ADIS IMU

Hardware

The Analog Devices "ADIS" ADIS16400/ADIS16405 "Triaxial Inertial Sensor with Magnetometer" is a device we will mount to a GFE board.

The specific part number we have is:

The ADIS has a SPI interface which we will use to configure and read the device in operation. ADIS-IMU-view1.png

Pin Connections GFE <-> ADIS

  LPC23xx Dir (ADIS)         LPC2368 PIN    ADIS PIN  Notes
  --------------------------------------------------------
  SCK     --> (SCK)               62           3      SPI interface
  SSEL    --> (_CS)               63           6      SPI interface
  MISO    <-- (DOUT)              61           4      SPI interface
  MOSI    --> (DIN)               60           5      SPI interface

  P1.29   --> (_RST)              45           8      Reset controlled (pulled high; IMU not reset by default) 
  _EINT1  <-- (DIO1)              53           7      Acquisition ready (Set MSC_CTRL in ADIS to make DIO1 active low)
  _EINT2  <-- (DIO2)              52           9      S
  P0.5    <-- (DIO3)              80           1
  P0.6    --> (DIO4/CLKIN)        79           2
  N/C         (AUX_DAC)                       20      Not used: not to connected, but goes to pin
  GND         (AUX_ADC)                       21      Not used: grounded via resistor
  ---------------------------------------------------------------------------------------

Software