Troubleshooting Wireless Issues

Overview

Streaming lots of data to your computer wirelessly is technically challenging. This is especially true for our system, where synchronized, high sample rate data is sent with minimal latency and without loss of data. When things go wrong, it can sometimes be difficult to tell what the issue is. Am I out of range? Is it wireless interference from the WiFi router next door? Did the battery die on a sensor? Is something broken?

APDM's wireless sensor system was designed to provide feedback to help diagnose common and uncommon problems with wireless connectivity. This is primarily done through visual displays on the devices, but the LEDs also convey important information that can be viewed from a distance.

Understanding the main access point display screen

In order to stream, all configured Opals need to be undocked and powered on. If you wish to use a different set of Opals, you must reconfigure your system through your APDM software (Motion Studio, Mobility Lab, etc.).

The access point's main display screen has a list of the Opals that are currently configured. It displays their ID, their label, and the current wireless signal strength. On the far left is the wireless state indicated by one of 3 characters:

  • '!' indicates that the access point has not received any data from this Opal for at least 5s.
  • 'X' indicates that the access point is currently receiving data from the Opal, but has not yet established the data stream.
  • '.' indicates that the Opal is ready to stream.

The status of the AP will only change from "Not Streaming" to "Streaming" when each configured Opal is ready to stream and has started sending its data wirelessly to the AP. The AP will therefore be in the "Not Streaming" state if any one of the configured Opals is not ready to stream. This includes

  • when the Opals are docked
  • if any of the Opals are out of range of the AP,
  • the AP has been power cycled (e.g., unplugged and replugged) but has not yet received the necessary data from each Opal to start the streaming session.

Understanding the access point LED sequences

  • The LED is solid blue: The access point is unconfigured. You must configure your system for streaming.
  • The LED is solid green: The access point is not streaming data, because at least one Opal is not communicating 
  • The LED displays a brief green flash every 2s: Everything is going well. The access point is getting data from all monitors and overall latency is low (the most latent Opal is at most 5s behind)
  • The LED displays a long green flash every 2s: The access point is receiving data from all of the Opals, but the overall latency is high (the most latent Opal is at least 5s behind)

Understanding the main Opal display screen

The main Opal display screen has 3 main indicators:

  • The label: This text string will be associated with this Opal's data in any resulting recordings
  • The wireless signal strength: This provides a measure of the signal strenght. Note that this metric is very sensitive, and will rarely be above 95%. Data can stream down to values of 5%, but it may become more latent at this level, as ambient wireless noise can start to interfere with the signal.
  • The battery level: This provides a visual indication of the charge level, in addition to an estimate of the remaining runtime.

Understanding the Opal LED sequences (when undocked)

  • The LED is flashing red: This indicates that there is an error on the Opal. Docking and undocking the Opal may resolve the issue. Reconfiguring the Opal is a next step to try if the red blinking does not stop. Contact APDM customer support if this continues to be an issue.
  • The LED is flashing yellow: The battery is low
  • The LED displays a brief green flash every 2s: Everything is going well. The Opal is streaming data to the access point and the latency is low (at most 5s behind)
  • The LED displays a long green flash every 2s:The Opal is streaming data to the access point, but the latency is high (at least 5s behind). This is typically an indicator that the Opal is out of range, that there is wireless interference, or an Opal is otherwise blocked from communicating with the access point (e.g., on other side of a subject in a large open space where reflections are not possible).

 

Troubleshooting

You are unable to start a recording session. In Mobility Lab, this may manifest as an error when you try to start a trial or after a trial within a sequence.

  • Check the access point to see if it is streaming. If not, see below.
  • If it is streaming but the access point has a long, green flash, see below.

The access point is solid green. This means that the access point is not streaming because it has not receiving data from at least one of the configured sensors in the last 5s. This may be true if:

  • Not all of the sensors are undocked. If this is the case, undock all sensors and wait several seconds for the access point to blink green.
  • One or more sensors has run out of battery.
  • One or more sensors is obstructed somehow. For example, a sensor may be worn on the lumbar of a subject sitting in a metal chair, etc. Remove the obstruction to confirm that the access point returns to flashing green.
  • There is wireless interference. See this guide for more information on how to choose a good wireless channel.
  • One or more sensors is out of range. The range is 30m line of sight, but can be significantly reduced when other wireless signals on the same channel are present or if there is not clean line of sight (e.g., the Opal is on the side of a subject facing away from the access point). Also note that the signal tends to radiate in the same plane of the Opal's display, as the signal does not transmit strongly through the glass screen.

The access point LED has a long, green flash (50% on, 50% off). This indicates that the access point is receiving data from all of the sensors, but there is interference of some type that is making one or more sensors at least 5s behind in its data transmission. This isn't necessarily a problem, as all of the data will ultimately be streamed. You may have to wait for a bit when the recording is stopped for all of the data to complete streaming, however. Possible causes:

  • One or more sensors is obstructed somehow and making it difficult. For example, a sensor may be worn on the lumbar of a subject sitting in a metal chair, etc. Remove the obstruction to confirm that the access point returns to a quick flash green flash (10% on, 90% off).
  • There is wireless interference. See this guide for more information on how to choose a good wireless channel.
  • One or more sensors is nearly out of range, and can only send small amounts of data. The range is 30m line of sight, but can be significantly reduced when other wireless signals on the same channel are present or if there is not clean line of sight (e.g., the Opal is on the side of a subject facing away from the access point). Also note that the signal tends to radiate in the same plane of the Opal's display, as the signal does not transmit strongly through the glass screen.

To determine which sensor or sensors are having trouble communicating, look at the access point's main display screen. See details in this article above.

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