Charge 6 HR broadcasting incompatibility: I'll evaluate workarounds, please share your setup

[supercurio]

Hi 👋

I just upgraded from a Charge 5 to 6 in order to gain the heart rate sensor broadcasting "HR on equipment" feature.
As documented in DC Rainmaker's review and several threads here, its compatibility is problematic since it requires bonding (pairing) before sending the precious sensor data. That's supported in the Heart Rate Profile standard specification but highly uncommon, therefore many devices don't get the HR data and don't have the ability to display an error message either.

I'd like this to work for myself and I have years of experience developing Bluetooth Low Energy stuff, so I'm getting started with proof of concepts to see what can be done address incompatibility.

1. As a mobile app.
2. Running on a micro-controller (either nRF52 or Pico W)

I'm anticipating a few pros and cons with both approaches on which I can expand further later if you'd like to know.

But first, would anybody else be interested?
Typically I'm thinking

• that it could be pretty useful to a cyclist hoping to add HR data on their cycling computer's recordings
• if your treadmill can't pair with the Charge 6

What else?

If there's interest then I'll look into it further based on your needs, otherwise I'll probably hack something together that works for me as quickly as possible.

Cheers,

Reference:
Heart Rate Service 1.0, 5.1.2 Connection Procedure for Bonded Devices 

[Triletics]

@doctordarko not Strava (I don't use Strava with Fitbit because Fitbit Strava support is useless for me, my Strava account is associated with Garmin) but here's one of recent rides HR comparison (and you can see also other differences because Charge 6 accuracy is far from perfect in other areas):

As you can see, this as well could be just a set of random numbers out of Charge 6. Not much use for me.

[doctordarko]

I am genuinely gobsmacked by garbage HR you are observing. 

Zwift ride tonight with HR strap in red and Charge 6 in blue. Took a few tries with different activity profiles (as I do not record activities on Fitbit) but eventually settled on Aerobics (~8min mark), with just a timer and HR so I could export data for this comparison later. Anything but garbage. Go figure.

[Triletics]

@doctordarko Zwift and outdoor are two differenr things. Outdoor depends on surface you ride one, all the vibrations, etc. I see usually no issues with indoor rides.

[supercurio]

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@doctordarko wrote:

Strava or it didn't happen! 🤣 I log all the rides as a week of riding to work is up to 80km depending on which way I go. It all adds up. 

I find both Charge 5 and now 6 okay for HR when riding in comparison to the strap. Can be bit laggy but does good enough job. 

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😆  just when you wrote this I finished a 80km ride, testing the native Charge 6 broadcast to the original Wahoo ELEMNT BOLT
And it's on Strava indeed! https://www.strava.com/activities/12122437492

I was happy with the HR performance, with the Charge 6 on my left arm vs the Forerunner 645 on my right, which was significantly laggier and had false 180 bpm readings at times caused by vibrations. I was riding with power meter pedals and when getting out of saddle during climbs at higher watts, the Charge 6 was HR was responsive enough to be useful, whereas the Forerunner was too slow and inaccurate to be. On steady-state efforts, both were showing the same value.

After roughly 3h, the Charge 6 gave an alert of 20% battery left, so I guess that it won't do the trick for 5h+ rides.

In terms of compatibility, I'm happy that this use case with the Wahoo ELEMNT BOLT updated firmware does not require the app I was thinking about writing.
How's the compatibility with Garmin Edge bike computers nowadays?
I might still need this HR relay app later in the season for Zwift: TBD.

[mikey_pdx]

I've been using the HR broadcast feature for a while now with my iFit NordicTrack s15i bike.

In my experience, @doctordarko  you're correct - the C6 does always want to start an activity once connected to the bike. I have to scroll to choose 'Spinning', but at least the activity list is limited pretty much to typical machine-centric ones. I connect it from the main screen of the bike's interface, so it's broadcasting (and recording an activity) while I'm idly pedaling and scrolling through the workouts on-screen to select a ride. I can connect/disconnect after I start the ride, but...

...sometimes it doesn't connect first-time, so I always start before I select a ride and start it rather than eff around with it to get it to work while I'm actively trying to work out. I figured out that turning BT off on my iPhone helps in those situations. I think sometimes the C6 just doesn't want to connect to anything else if it's connected to the phone. Happens maybe 30% of the time. Once it connects to the bike, I can turn BT on my phone on again and no problems.

I've only ever had the connection drop mid-ride once, and that was early on, maybe the 2nd or 3rd time I tried it. Hasn't happened since. I don't recall if that was before a firmware update or not.

I have a minor annoyance about what the C6 does post-ride after I've stopped the activity, but it's not a huge deal. Overall, pretty pleased with the feature in my particular application. I wish my rowing machine had the capability.

[doctordarko]

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After roughly 3h, the Charge 6 gave an alert of 20% battery left, so I guess that it won't do the trick for 5h+ rides.

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Unlike some others, my experience with Charge 6 HR has been very positive. It's a 24/7 device I wear, so happy to know it can now be used as a backup HR device for commutes or shorter rides. First time I tried broadcast feature it didn't even register on Wahoo Bolt and Roam, so something has definitely been updated recently.

Some nuisances as @mikey_pdx pointed out with what Charge 6 does while broadcasting but feature is useful overall.

[tannenba]

Re Polar Verity Sense (at least the current model which I own): it does have an explicit “swim mode” which disables Bluetooth and records lap count and heart rate into onboard storage/cache.  You can store dozens of swims. Then at your convenience you sync your workouts to the Polar Flow app, which can be connected to automatically sync to Strava et all.  Works well, but there is no “display” in the water to get any feedback while swimming. Guess this is all very similar to Polar H10, except optical sensor, and I find having the small sensor attached to my googles less obtrusive then a chest strap when in the pool. I do use a Polar H9 chest strap cycling with a Wahoo Bolt… but I’m happy to read that apparently the Charge 6 is working with the Bolt now for folks, can’t wait to try! 

[Triletics]

@tannenba Verity Sense has no offline cache though so you can sync swimming into Flow as separate activity but you can't add HR offline to activity tracked with watch (PolarH10 has a cache made for it) so when you swim you can see HR whenever connection is restored and gaps will be filled upon syncing the watch. Of course, offline cache for H10 works only with Polar watches same as offline cache of Garmin's HRM straps works only with Garmin watches (one thing nobody wants to standardize).