ANT Forum

Hello,

I am using the BikePower within an Android App. It basically subscribes to the onNewCalculatedPower event and displays them. Very much like the PluginSampler App. However, I am getting negative readings for a long time, before the values switch back into positive.
This is done using a SRM powermeter.

Do you have any suggestions, where these negative values (also for torque) come from?

BEst regards and thanks for the support.      

Hi,

Are you receiving exactly "-1" from the calculated power and calculated torque events?

What value are you receiving on the dataSource flag?

Do these negative values continue after you've restarted your app?

Best regards      

Hi,

no, I'm receiving negative power values. The numbers are within a typical power range, however the sign is minus. Within the code, I set the AutoZero function to true:



and there after, I register for claculated power, torque and cadence events.

From time to time, the first power events are negative. Then, after stopping to pedal for a couple of seconds and starting again, the values are positive.
If I keep pedaling while receiving negative values, the values stay negative.

The data source flags are as expected:
* first value: CTF_INITIAL_VALUE
* afterwards: CTF_DATA

If you have any idea where the problem, I would be very thankful.

Best regards,

twich      

Hi,

Thank you for the information. We have identified an issue with how CTF calibration values are handled by the plugins and will be resolved in a future release.

In the meantime if you need to move forward quickly, you may use the raw CTF data event to calculate Power/torque using the zero offset value from the calibration message event.

In order to gather an accurate zero offset value, the most recommended method for accuracy would be to create an Activity/screen/feature/etc to request the user to wake up the SRM, and then to stop applying any pressure to it. This will cause it to automatically send zero offset values (or call the request manual calibration method) which you can use to calculate torque or power.

For more information please refer to the ANT+ Bicycle Power Device Profile.

Best regards