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]

But why? Isn't it easier to get proper HRM that connects via ANT+ and BLE to anything? 🤷 If somebody uses bike computer then most likely will use chest strap because wrist HR is too inaccurate during cycling (wrist positioning and vibrations from riding). Treadmills pair with any external HRM via ANT+. You stand on it and instantly see your HR. Ok, workarounds for fun of development could be interesting. Practical value - none.

[supercurio]

Why is a fair question, I can only answer for myself.

I wear my Fitbit Charge at all times since I value the insights from continuous tracking.
When I'm running, I wear a Garmin Forerunner 645 because it's reliable and has good enough GPS accuracy (Charge hasn't)
I've been running with my Polar H10 chest strap for HR accuracy but it's an unpleasant experience as it inevitably ends up sliding down and after 40min+ I struggle to keep it in place while running.
So I'd like to use the Charge 6 as HR sensor because my Garmin's is so-so, and I find checking where my HR's at useful sometimes while running on trails.

For cyclists, imagine a daily commuter recording their ride to work on their Element Bolt. The charge 6 isn't perfect but can be surprisingly good tracking HR when cycling outdoors as shown by The Quantified Scientist's review (timestamp).

As you can see, there's absolutely a rationale behind this. I disagree that wrist HR is too inaccurate in the scenarios you describe for all devices as nowadays, the Charge 6 and Apple Watch are capable enough.
I understand that you don't have this need which prompted you to reply negatively, but based on other messages on this forums I'm not the only one hoping to connect a Charge 6 to an incompatible device.

[Triletics]

@supercurio I wear Garmin HRM+ strap and it doesn't slide but two or three times it opened. If you don't like chest strap try Polar Verity Sense. Is optical sensor but with accuracy very close to the chest strap and you wear it on bicep/forearm/calf. It's best alternative for chest strap and supports ANT+ and BLE (2 connections via BLE). My wife prefers Verity because chest straps are not really designed for women for obvious reasons 🤷 Have you tried that Polar armband? It even counts swimming length in swim mode (attach it to goggles).

My response wasn't supposed to be negative. It's Fitbit who should fix the problem not users and users have plenty of options that actually work. Fitbit is just lucky that most of users have no idea those options exist.

I mostly run and posted here many analysis of C6 vs chest strap. Main problem with C6 is that it locks onto the cadence (so I get HR of nearly 200). Considering that broadcasting would work, there is another problem - data accuracy. With broadcasting feature Fitbit tried to solve non-existing problem while it should implement external HRM connectivity instead. Broadcasting on the other hand could be implemented as in-app feature (app can see real-time HR) and that would make it watch-independent (so even old models could broadcast HR). With doing some research they could even implement ANT+ connectivity (some Android apps support it like Zwift, if phone doesn't then little USB dongle solves issue and ANT+ starts working).

Before implementing anything, Fitbit should do a thourough research to know what's already out there and how others implement similar features. If we start solving problems created by Fitbit then Fitbit has no reason to work on fixes if there are workarounds (which in the past was often an official answers directing users to workarounds as a solution).

[Triletics]

@supercurio one more thing if you really want to do it. Do it via mobile app. Much easier (and such app would be easy to use by anyone). App as client for C6 (or any other HRM) and server for other apps/devices. Add ANT+ so it will be even simpler to use (no pairing necessary). That may work. To be honest, such a proxy app could be useful for any kind of sensor (ie. Stryd that supports single BLE connection but AW users sometimes want to be connected both to the watch and phone app but they can't) 👍

[supercurio]

Thanks @Triletics I appreciate all the in depth feedback.

Funny you mention Polar's Verity Sense, I was looking into it recently as an option as well as alternatives in this form factor. I'll keep it on my watchlist in case the Charge 6 doesn't perform well enough on me.
Unfortunately I lost confidence on my Polar H10 as its reliability fell of a cliff since its last firmware update, producing obviously inconsistent results while for both running (outdoor) and cycling (indoor). On top of the comfort aspect.

Awesome that you've already conducted your Charge 6 accuracy tests. Cadence lock on a modern HR algorithm is a bummer for sure. I didn't know and will keep an eye on that.

Totally agree that Fitbit should have support for external HR sensors for generations. The list of bugs and outstanding missing features in the Fitbit ecosystem is striking. Their prioritization can be puzzling, no doubt about that.
For me, it's more satisfying to look into DIY some kind of solution instead of trying to convince Fitbit to do anything - I've tried before.

On ANT+, I don't expect Fitbit to go there, nor I would encourage any manufacturer to go in this direction since in most cases it means depending on a Nordic Semi IC (expensive) with a software & wireless stack that was deprecated in 2021.

On implementing a HR data relay as a mobile app absolutely! It will have the benefit to allow many simultaneous connections, a desirable feature for sensors supporting only 1 Bluetooth LE connection.
Extending the scope, it could also group HR, Power, Cadence, FTMS under a single connection that could help Zwift Apple TV users.

I'm anticipating a user experience roadblock with using a mobile app as relay however since each session will be advertised as a new MAC address, something that's enforced by mobile OS for privacy reasons. It might not be a problem in some use cases but a massive annoyance to a Garmin Edge user for instance.
That's the reason why I think Fitbit didn't consider implementing HR broadcast from their app and had to do it on the band instead.

That's the first think I'll prototype.

By the way ultimately I got this Charge 6 as a HR sensor while walking on an under-desk treadmill I ordered. I'm also making an app to track that automatically.
Since I plan to walk on it hours a day every day, the fitness tracker I'm already wearing on my wrist beats every other option.

[tannenba]

I’m interested. Subscribed to this thread. Would like to use the Charge 6 with Zwift (Windows Desktop), as Charge 6 is accurate enough considering I’m training with a power meter anyhow. Same with cycling outside, would like to use it with a Wahoo Bolt v2.  Thanks! 

[Triletics]

@tannenba you may be able to get it working with Zwift on PC but unlikely it will work with Wahoo Bolt v2 (so far, I didn't get it working with any bike computer).

[supercurio]

Thanks for showing interest. At the moment I don't have use for the project I've described and I've started working on other projects so it's paused.

Like @Triletics described, I've noticed the Charge 6 to be very prone to cadence lock when running. On me it's bad enough that it makes it basically useless for running, messes up fitness tracking and is a significant regression VS the Charge 5 I had before. On some runs, I have 20 to 30% of HR between 175 to 190 bpm, reflecting my average cadence of 180.

So that's a bummer, but for other activities the HR sensor is pretty responsive.
@tannenba, did you evaluate its accuracy for your indoor cycling?

Zwift on iOS has troubles with the Charge 6, which requires un un-pair and re-pair each time. Is it the same on Zwift Windows?

[redevill]

I really like the HR monitoring on my Charge 5, and found it good for indoor trainer use (rollers) and was planning on a charge 6 to get the "broadcast" feature. I was hoping it would pair with my Garmin Edge. If I didn't misunderstand, sounds like the charge 6 doesn't cut the mustard...?

[tannenba]

Hi @Triletics - if you have any tips on getting the Charge 6 to work with Zwift on PC, I’m all ears. So far I’ve been able to get Zwift to see/pair with the Charge 6, but no heart rate data ever appears. I’ve tried pairing with Zwift alone, and also pairing first with Windows Control Panel. Same result. Using Windows 10, Bluetooth USB dongle that works fine with all other equipment I’ve tried (including a Polar H9). 

[tannenba]

@supercurioFor indoor cycling my Charge 6 HR data seems to come surprisingly close to my Polar H9. I do shove the Fitbit pretty high up my arm for a snug fit when cycling, but still, the Charge 6 HR does seem improved from my Inspire 3. Just a bummer I can’t get it to work with anything external I care about. Also a bummer that it apparently does not record heart rate at all while swimming, although recording HR at the wrist while swimming is notoriously inaccurate. For swimming I recently started using a Polar Verity Sense attached to swim googles (so it records at the temple) which works great. 

[Triletics]

@tannenba I haven't got it working Zwift on PC. I was more lucky on the mobile phone but that is also lottery. Sometimes it works (Charge 6 shows prompt to pair) but most times the prompt doesn't appear.

Charge 6 tracks HR while swimming if you let HR to be auto-recognized (but first, enable water lock in tracker settings to lock touch screen). That came as a biggest surprise. Now, I consider Charge 6 the worst Fitbit I ever owned but this one thing surprised me a lot - HR while swimming was quite accurate comparing to Garmin HRM Swim strap. In fact, I was surprised that Fitbit didn't give an option to track HR in water but I don't believe they ever tested that accuracy and it would come as a surprise to them, too 😆

Verity Sense is nice in water but the problem is that it has no cache and even if it had (like Polar H10) it would work with Polar devices only. Problem in the water is that connectivity breaks easily. Did you notice that Verity Sense can count lengths? Pity, it doesn't seem to detect the swim style (each style has quite a unique head motion, maybe except butterfly and breaststoke). I approached Polar about it but they have no plans to add swim stroke detection. Pity.

[Triletics]

@tannenba see this post (swimming test I have done shortly after I got Charge 6):

https://community.fitbit.com/t5/Charge-6/Little-review-and-tests-running-swimming-rowing/m-p/5483231...

This is really good result and I reproduced this level of accuracy multiple times. However, unlike HR, laps were always wrong. Pity, my Charge 6 got damaged by water eventually 😑

[doctordarko]

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For cyclists, imagine a daily commuter recording their ride to work on their Element Bolt. The charge 6 isn't perfect but can be surprisingly good tracking HR when cycling outdoors

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My commute is 15min/7km ride that I don't bother wearing HR strap riding to work, so ability to use Charge for HR would be ideal for me.

[supercurio]

An update on that, I've tried the HR on Equipment feature with the Wahoo ELEMNT BOLT right now, as I'm back to cycling after a long hiatus and it just works!
Not even the V2 model, the B&W model with updated firmware.

Yesterday I was comparing the HR while cycling between my Charge 6 and Forerunner 645 Music, and the Charge 6 seemed HR seemed to raise quicker on intensity peaks. I haven't compared to my Polar H10, but it seemed encouraging.

[doctordarko]

Well, I'll be **ahem**ed!

Just tested it on my ELEMNT Roam (in bed about to go to sleep) and it connected! Something definitely got updated in the last month or so since I upgraded to Charge 6.

Charge appears to want to want to automatically start an activity with HR broadcast enabled, which is not ideal but it's looking promising. 

[supercurio]

Yes after enabling the feature, the HR broadcast appears to actually begin only after the activity chosen start. I don't mind recording a cycling activity via Fitbit at the same time 😌

[Triletics]

@doctordarko for me, no Fitbit including Charge 6 is not even close to real HR on the bike (outdoor). HR I get for bike rides is very random. Also, for 15min ride I don't bother with bike computer (usually, no need for navigation on short known route).

[doctordarko]

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.