The Short Range Active Marker

The Short Range Active Marker consists of a driver unit capable of driving up to 32 markers through four daisy-chained outputs. The markers are small and lightweight and can be attached to the skin with simple double adhesive tape. The driver has an integrated battery which can either be charged in the driver unit or replaced with another battery and charged in a standalone charger. The battery is selected to last a day of normal measurements.

The use of the Short Range Active Marker (SRAM) can be beneficial in the following situations:

  • Tracking of reflective objects or in a reflective environment
    When tracking reflective objects or in an environment with many reflective elements, the use of active markers helps to avoid the interference of extra reflections otherwise caused by the strobes of the cameras.

  • Simple marker identification
    The sequential coding makes the identification very simple. The AIM functionality for passive markers can be just as effective as sequential coding, but in some setups the active markers can be easier to use. For example irregular movements of single markers cannot be handled by AIM and then the active marker is the best solution.

  • Outdoors
    The high intensity of the active marker allows for effective tracking when outdoors at frequencies up to 500 Hz.

The active marker hardware consists of the following parts:

  • A driver for up to 32 markers.

  • Selectable number of active markers on different chain lengths, and up to 4 marker chains with a maximum of 8 markers per chain.

  • IR eye

  • 2 batteries with power supply and an external battery charger.

  • Belt clip for driver

  • Sync cable [Not included in the standard kit]

Short range driver

The driver is the center of the short range active marker. It has to be attached in a secure way to the subject to make sure that there is no strain on the cables. The active marker kit includes a belt clip that can be attached on the driver to fasten it for example on a belt.

The driver controls and powers the active markers and has the following connections and indicators.

  • Markers 1-32
    4 connectors for the active marker chains. There can be up to 8 active markers on each chain and therefore there can be up to 32 markers on one driver.

  • IR in/Sync In
    Connector for the IR eye or Sync in. The standard use is to connect an IR eye to the input, The eye is triggered by a modulated pulse from the Oqus camera.
    The sync in signal must be coded to be correct and must therefore be sent either from another active marker driver or from an Oqus camera with the sync out signal set to Wired synchronization of active markers.

  • Sync out
    Use the Sync out connector to daisy chain several active marker drivers to one IR eye. Connect the Sync out signal from one driver to the Sync in connector on the next driver.

  • Charge/ 9 VDC
    Use this connection to charge the battery with the supplied power supply. The driver can still be used while it is being charged.

    Do not use the driver with the power connected while the driver is mounted on a person.

  • ON/OFF
    Turn on the driver by pressing the button. Turn off by holding down the button a couple of seconds.

  • Driver ID
    Change the driver ID to specify which sequential range to use for the driver. The possible ranges are 1-5, which corresponds to the IDs 1-32 to 129-160. 0 means that the sequential ID is turned off.

  • Battery indicator
    When pressing the power button, the four LEDs indicates the battery status. One LED means that you soon have to charge the battery.

  • Status indicators
    The three status indicators at the top displays the following information:

    • Power/Batt Low
      The LED is lit green when the power is on and starts flashing green when the driver goes into the power save mode. The battery is low when the LED is lit or flashing red.

    • Charging
      The LED is lit green when the driver is being charged, if something is wrong the LED is lit red.

    • Sync active
      The sync is active when the LED is flashing orange.

Active markers and IR eye

The active markers are mounted on a daisy-chained wire that can have up to 8 markers and a length of 3 meters. The size of the markers is comparable to 12 mm passive markers. The ID of the markers is decided by the connector on the driver. When a chain has less than 8 markers the other IDs of that connector will be skipped, e.g. if you have chain of 4 markers connected to the first two connectors these will have ID 1-4 and ID 9-12.

The IR eye is mounted on a short wire and can be mounted anywhere to detect the pulse from the camera. It has an adaptable sensitivity so it can easily detect the pulse in almost any setup, even outdoors.

Battery and charging

The battery in the short range active marker is a rechargeable Li-Polymer battery. It can power the active marker for a day of normal measurements. The battery can be recharged either in the driver with the power supply or separately in the battery charger. It takes about 3 hours to fully charge the battery.

Do not use the driver with the power connected while the driver is mounted on a person.

To remove the battery, press the button on the side of the driver and lift the bottom lid. Make sure that you insert the battery according to the image inside the driver.

Short range active marker specifications

Driver

83 x 52 x 15 mm, 99 g
IR marker D 16 x H 11 mm, 3 g
Frequency range 1 - 500 Hz
Number of markers per driver Up to 32 markers
Total number of markers Up to 5 drivers can be used,
up to 160 sequential coded markers
Maximum measurement distance more than 25 m
Battery time, 200 fps, 16 markers 4.5 h
Time to fully charge battery 2-3 h