In general the Yabby operates in a similar way to the Oyster and Remora. There are some key differences in order to optimise the battery life given the lower capacity batteries, and to ensure consistency between both the Wi-Fi and GPS versions. In particular:


  1. The Yabby by default is not set up for trip tracking. The Oyster and Remora log a position every 2 minutes when in trip. By default the Yabby simply records the beginning and end point of movement. They Yabby should be thought of as a location/movement detection device rather than detailed trip tracking device. 
  2. The accelerometer alone is used to detect movement. It is impractical to check the Wi-Fi signal for movement, so it is not done for the GPS version either


How the Yabby Locates


GPS

The Yabby GPS uses its GPS module to determine its position, as per Digital Matter’s other devices. Indoor or dense urban environments can greatly impact GPS performance, sometimes leaving devices unable to get a fix.


Wi-Fi

  • The device scans for Wi-Fi Access Points (Wi-Fi Routers) and records the signal strength received from each.
  • The locations of these access points are known.
  • The device sends the signal strength information to the server
  • The server calls Google’s Geolocation API, which uses the information to triangulate the device’s position, based upon its proximity to various Wi-Fi routers.
  • If Wi-Fi signals cannot be found, the device has cellular fall back – it will determine its position based upon which cellular tower it is communicating with. The accuracy of this measurement will not be great (potentially ± 1km), however it will give an idea of where the unit is.

Wi-Fi signals can be received indoors (even basements) and in dense urban environments, hence Wi-Fi geolocation has the ability to provide a position where GPS will not. In practice, in an urban environment, accuracy should be around ± 30m


How the Yabby Detects Movement

The Yabby uses its accelerometer to detect movement. Operation is as follows:


  • Accelerometer wakes the unit
    • By default, a wake filter is applied. The filter only starts a trip when it has seen 1 second’s worth of above-threshold movement in a 4 second period, or repeated short movements over several 4 second periods. Disabling the filter results in any accelerometer movement above the Wakeup Threshold (in Accelerometer Settings section of System Parameters) waking the unit.
  • Unit immediately determines it is moving – this is equivalent to entering a Trip for other DM devices
  • Once moving, the accelerometer no longer wakes the unit
  • It wakes every two minutes on a timer, and does two things
    • Asks the accelerometer if there was any movement in the last 2 minutes
      • If it is time to log a position, it gets a fix and records it
      • Once the accelerometer claims there has been no movement for a while, the default is 5 mins (Movement End Time parameter), the device decides movement has stopped.
      • The GPS version will also wait until the speed reported by the GPS has dropped to 0, to prevent movement ending when the movement is very steady and constant – e.g. a train where acceleration is minimal


Uploading can happen before, during and after movement, optionally. The default is before, after, and no uploads during movement.

Heartbeats happen if there has been no upload for a long time (heartbeat period).