Bluetooth 2.0 not reconnecting

[Engenia]

I have built a 10 Hz Bluetooth GPS from a BT04-S Bluetooth/serial module and a Reyax RY82530 GNSS Receiver module. It is very cheap and is 8-10x faster than the standard phone GPS. There is only one problem with using it with HLT. It has to be forgotten and re-paired whenever it is powered ON.
Normally I would expect BT 2.0 to remember the last pairing & simply reconnect next time the two meet, and they do. HLT will reconnect, but no data will flow.

Today I was trying to get a handle on the issue and came across an Android BT GPS app called "Bluetooth GNSS" that connects to the BT GPS and presents the data to Android as if it were originating from the internal GPS. When HLT is then run, the GPS source does not need to be selected. It reads the "internal" GPS stream as normal, but the rate is now 8 - 10 Hz.

If I shut down the BT GPS and power it back up, it immediately enters pairing mode and then "Bluetooth GNSS" takes over and reconnects. HLT continues as before, at 10 Hz.
Curiously, after several minutes of reporting the internal GPS as the source, HLT changes over to reporting BT04-S as the source, with a dropout of a few seconds.

I wonder if HLT could do this without the "Bluetooth GNSS" app as an intermediary?

[this on a Nokia 5.1 running Android 10]

[Harry]

Hello,

These helper apps are around because Android does not come with a generalized integration of external sensors (like iOS with MFi). They poll the GPS and feed it into Android so any app using the "internal GPS" benefits from the usually better accuracy and rate.

In LapTimer the rule is "either use an helper app *or* add the paired sensor to Sensor List". Once you do both, you will get all kinds of conflicts around connection making and communication.

By adding a BT device in Sensor List, LapTimer communicates to the sensor directly.

LapTimer does not fiddle with pairing itself. Instead, the BT+ button in Sensor List presents what is paired already. Selecting an item will make LapTimer memorize this pairing identity permanently. In case the device is unpaired and paired again, chance are good, a new identity is instantiated and LapTimer cannot find it again.

So in case you want to use LapTimer's direct integration, make sure the pairing of your device is permanent. Maybe you can influence it. Otherwise, use the helper app and do not add the sensor in Sensor List.

- Harry

[Engenia]

Thanks Harry. I didn't realise that I could add the BT sensor to the list.

However, to try it out, I disabled the helper app, connected the re-powered BT sensor at the phone then started HLT. Then went to the sensor list and added the BT04 to the list using the BT+ button. HLT showed that it was connected, and not the internal GPS, but no data arrived. I let it run for several minutes, but nothing happened.

I then removed the BT04 from the sensor list & started the helper app. It began gathering data, which I allowed it to forward.
Back over at HLT, it reported the local GPS receiver, but the rate was 8-10 Hz.

Did I follow the correct procedure to make HLT gather the BT04 data?

[Harry]

Yes, provided the helper app has been really killed. They usually fiddle with the sensor from background. The only other thing you can try is tick the Insecure BT Connection Expert Setting. For some devices, it is required.