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New sensor with ANT+ based on AutoLap in Garmin

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Total Posts: 3

Joined 2021-11-15

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Dear Mister,

We would like to start a project but first we want to make sure that it is feasible.

A sensor with an ANT+ module sends time data in milliseconds to a Garmin device.
The goal is to synchronize the data with other sensors (e.g. heart rate sensor, power sensor, altitude, distance) to make a correlation between the different parameters.

The Garmin device has the Auto Lap mode. It would be replaced by our sensor.

Thanks for your answers

     
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Total Posts: 370

Joined 2012-06-27

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Auto lap functionality modification is not available to 3rd parties. You would need to write a Connect IQ Device App that uses Toybox.ActivityRecordingSession and write laps using addLap() based on information received by setting up an ANT channel to receive from your sensor (https://developer.garmin.com/connect-iq/api-docs/Toybox/Ant/GenericChannel.html).

Note: HR, power, and other ANT+ sensor data is not timestamped to be able to correlate directly with another sensor.      

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Ian Haigh

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Joined 2021-11-15

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Hi guy,

Thank you for your answer.

Concerning your note, you mentionned that is not possible to correlate with another sensor.

In garmin connect, HR and power are correlated. So how can we add another information ?      
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Total Posts: 370

Joined 2012-06-27

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You can add developer data to the FIT file to add additional information with plotting in GC https://developer.garmin.com/connect-iq/api-docs/Toybox/FitContributor.html

A timestamp is part of the record message, but this is the time the recording occurs, not the time the value was measured. It is also lower resolution than the milliseconds resolution you mentioned above. For HR, power, etc the difference between the time of recording and when it was measured is not critical. A single record message is logged that includes the timestamp as well as all data for that slice of time. The end user is able to configure the log interval to be once per second, or at a lower rate.      

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Ian Haigh

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Total Posts: 3

Joined 2021-11-15

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Do you mean we have to manage the timestamp in the Garmin Watch with Connect IQ App ?

If yes it means Garmin is doing the correlation with the timestamp of the watch and when the watch receives an event, it's recorded at this timestamp ?

Is there any delay durint the transmission from the sensor to watch in connected mode ? What is the transmission accuracy ?      
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Total Posts: 370

Joined 2012-06-27

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The native Garmin software handles creation of record messages, the interval at which they are created, and creation of the timestamp in the record message. As previously stated the interval can be controlled by the end user, but the default is 1 second record message intervals in most cases.

The CIQ app simply adds data to the next record message to be logged. This means that your data may in the worst case be logged and timestamped a second later than you made the call to log it.

With ANT there is at least a 1 channel period delay between when a measurement is made and when it is received by the watch. Depending on how the profile sets up the transmission pattern it may be more. Note that ANT is lossy. Every channel period a message is sent, but it may fail due to poor RF conditions. This leads to a data stream that is typically 1 channel period latent and has gaps.

Depending on the sensor algorithm there may be additional latency between when the measured value is determined and the time for which it was applicable.

End to end between the sensor and FIT record message you have
sensor algorithm latency + 1 ANT channel period minimum + up to one FIT record message period      

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Ian Haigh