ANT Forum

I've been stuck on this for ages but thought I'd had a break through only to get stuck again, I'm hoping you can get me over the brow of the hill.....

My mission is to gain a speed reading from the garmin sensor.
I've read the profile doc and understand the equation.

I've managed to put the hex values together to give the wheel revolution count. I watch these tick by on the screen as I spin the wheel on the bike. The issue is the time doesn't seem to update with the current time stamp when the wheel passes the sensor. The time count only increases by 257 (of 1/1024).


Below is a snapshot of some of the data I collected.
(the wheel is spinning slowly hence the rev count is not changing on every reading)

For background info i'm using Ant.core on python (demo 07_rawmessage3 if this means anything to anyone) with a garmin speed/cadence sensor and a garmin usb stick.

revs count time count time change
32686 8367790
32686 8367790 0
32686 8367790 0
32686 8367790 0
32687 8368047 257
32687 8368047 0
32687 8368047 0
32687 8368047 0
32687 8368047 0
32687 8368047 0
32687 8368047 0
32688 8368304 257
32688 8368304 0
32688 8368304 0
32688 8368304 0
32688 8368304 0
32689 8368561 257
32689 8368561 0
32689 8368561 0
32689 8368561 0
32689 8368561 0
32690 8368818 257
32690 8368818 0
32690 8368818 0
32690 8368818 0
32691 8369075 257
32691 8369075 0
32691 8369075 0
     

Are you sure that you interpret the correct bytes of the payload as the timer value?
The 257 increment looks as if both the major and minor byte of a 16 bit value are incremented by one.
Which in turn looks as if both values come from an event counter rather than a timer.

Cheers,
OMB      

Thanks for the answer.

I've been using payload 7 and 8 (bytes 8 and 9) for the speed event - I've assumed the payloads are ordered the same as the profile is set out.
This assumption is based on payloads 5 and 6 seem to capture the wheel revolution.
I'll play around with different payloads to see if I get other results.

thanks,
Rob      

You can confirm the payload structure by looking at the ANT Message Protocol and Usage Document (section 7).