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Simple BLE Broadcast Message

k.the.j
23 days ago

Hello,

I’m currently making a workout and track timing system for a side project. The system will automatically lap your Garmin watch as you cross the finish line, using a Raspberry Pi to track the times of everyone. Essentially it is a normal race timing system but instead of RFID chips, the garmin watches will record the laps and end times. Both the Garmin watches and the Raspberry Pi system will record the runner metrics, so everyone gets instant results of their own times after finishing, while the race or workout official gets to see all the splits and times of everyone on the Raspberry Pi system. I already have the Pi project developed, however, I need the simplest way to broadcast a BLE message from a Garmin watch with a specific UUID.

Here’s the setup I’m working with:

  • 8 runners (one for each track lane), each with a designated UUID.
  • The Raspberry Pi will scan for only those 8 specific UUIDs.
  • I do not need pairing or connecting to anything—just broadcasting a message with a UUID that acts as a runner ID or bib number.
  • The Raspberry Pi will listen for those 8 signals and use RSSI to detect when the watches come into close proximity, automatically lap the system, and record a time. This will eliminate the need for manual lapping while still capturing the watch metrics.
  • A data field will be the Connect IQ software responsible for broadcasting the Runner ID data. If necessary I can switch to an app, whatever is easier.
  • While RSSI may not be extremely accurate, I expect an accuracy of a quarter second or even worse, this is not of utmost importance as this is a prototype and really just a proof of concept (but I still plan on using it!).

I’m very new to Monkey C (I know next to nothing), and the BLE tutorials on the Garmin Developer site are a bit complex for what I’m trying to do. I've seen the raspberry pi project done by

Jim Miller, but I looked at the code and knew it was way too much for me to learn in a short period of time.

(https://forums.garmin.com/developer/connect-iq/b/news-announcements/posts/would-you-like-some-raspberry-pi-with-your-connect-iq)

I don’t need anything fancy—just a way to broadcast a UUID from a Garmin Forerunner or other watch, preferrably at a high frequency (10Hz or faster, I have no idea the packet send rate is on any specific watch though I expect it is different per watch model). 

Any help is greatly appreciated.

Thanks

  • 23 days ago

    The Garmins don't advertise.  All they can do is scan and look for advertisements.  What is sees in the advertisement is minimal, but the Garmin can then pair and send/receive.

    If you look at my samples in the blog post about the pi, the pi advertises it's UUID, and the CIQ apps look for a scan result with that UUID, and then pairs, and after it's connected does sends/receives,

  • 23 days ago in reply to jim_m_58

    Ok, thank you for the info and quick reply. Theoretically, how many watches can I pair to a raspberry pi at one time? If It can support 8 at a time that's all I need. (A little disappointing that it cannot broadcast, as if that could work, then ideally the system could read many more watches for races). Additionally, is it possible to broadcast via ANT+?

  • 23 days ago in reply to k.the.j

    I've never paired more than 1 with a pi.  Same with an ESP32. I've never had a need for more than 1.  Some BLE HRMs allow 2 or 3.  The Thingy52, what I started with, only allowed 1.

    With ANT, the sensor can broadcast, so with something like a Tempe, multiple watches can get data at the same time.

  • 22 days ago in reply to k.the.j

    I think that should work, but I only ever tried the other way. I don't know what you need to send. If it's only to know who is close then it could be enough if all the participants broadcast their HR. You can probably easily detect that, and take note of the ANT ID.

    If you need more data then you should try if CIQ code can broadcast

  • 22 days ago in reply to flocsy🤠

    I only need to broadcast a runner ID, like a bib chip timer that has the runner number, but over ANT

  • 22 days ago in reply to k.the.j

    That's more complicated. Why not the other way? At registration save the ANT ID of the runner's watch / strap? Added bonus, this works even with nom-Garmin watches that can broadcast HR via ANT, and most straps

  • 22 days ago in reply to flocsy🤠

    The problem is receiving this.  Not sure you can do  it with a pi.  I searched and I didn't get a clear answer.  Maybe an android phone instead,,,,

  • 22 days ago in reply to jim_m_58

    ANT? I don't think that there are phones today that have ANT. But it shouldn't be a problem with the pi or any computer with a USB ANT dongle.

  • 22 days ago in reply to flocsy🤠

    I've seen questions about trying trying to use an ANT stick with a pi, but I don't see any about how to get it to actually work..  It doesn't look to be as easy as you think.

    When I started with BLE on the pi, I was able to find some samples to get me started, but with the same code, they don't work with some of the latest libraries from github, so I stick with older stuff that works.