CGM connection - I've done my very best!

In principle, I would very much like to replace my Garmin — with its increasingly outdated interface and usability — with the Karoo. However, this requires reliable and permanent access to my glucose values (FreeStyle Libre), including operation without an active internet connection.

For accessing my FreeStyle Libre data, I use Juggluco, which works extremely well. Juggluco provides a local web server that simulates a Nightscout server, and access to it works flawlessly with Garmin devices.

Access through the Karoo using Henry’s app and Brennan’s app also works very well — especially when using a Wi-Fi hotspot connection. However, running a hotspot drains the smartphone battery significantly within just a few hours.

Because of this, my idea was to establish the connection via Bluetooth tethering instead. This also works in principle with both apps. Unfortunately, the Bluetooth setup process is complicated, not very transparent, and only reasonably stable under certain conditions and with a bit of luck. Nevertheless, I managed to stream glucose values via Bluetooth for more than two hours and display them successfully in data fields on the Karoo — without any noticeable battery drain on the phone.

Connecting the apps to the Juggluco web server via a Wi-Fi hotspot works as expected:

- Establish a Wi-Fi hotspot connection between the smartphone and the Karoo. In my case, the smartphone (gateway) IP was 10.176.90.35, and the Karoo IP was 10.176.90.82.

- Enter the connection details in the respective app: Nightscout URL: http://10.176.90.35:17580/sgv.json The token can either be omitted or replaced with a placeholder. 

- Start the connection and configure the data fields as desired — the Karoo then successfully displays the sensor data 😊

For the connection via Bluetooth Tethering I proceeded as follows:

- Bluetooth tethering first has to be enabled on the Karoo. This is only possible through hidden Android developer settings: Enable Developer Settings → open the “Settings” app via the “Apps” menu → Network Settings → enable Bluetooth tethering.

- Next, the Karoo must be connected to an audio device (e.g., my Sennheiser Momentum) using the “Bluetooth Audio” menu.

- Next on the smartphone, Bluetooth tethering must then be enabled. After that, a second Bluetooth connection can be established through the “Bluetooth Audio” menu (connect new devices). The Karoo appears as “Karoo BT Audio.” on the phone. If you couple the devices the BT internet access option should be activated!

- The smartphone IP address within the Bluetooth PAN then has to be determined, for example via Termux using ifconfig. In my case: 10.200.1.56. GlucoRoo or Henry’s app can then be configured with the following Nightscout URL: http://10.200.1.56:17580/sgv.json

- Once started, the sensor values are successfully displayed in the corresponding data fields 😊

Important observations:

- Without the simultaneous active connection to the Sennheiser Momentum, the Bluetooth connection to the phone (used for tethering) disconnects again after a few minutes (~2–3 minutes).

- If a Wi-Fi hotspot or regular Wi-Fi is enabled at the same time, the Bluetooth connection becomes unstable and the apps can no longer reliably connect, likely because the IP routing between Bluetooth and Wi-Fi is not handled properly.

- With Wi-Fi disabled and the above networking conditions respected, the Bluetooth connection appears to remain reasonably stable. Battery consumption via Bluetooth tethering is significantly lower compared to using a Wi-Fi hotspot  (<2h).

That’s everything from my side for now. I still believe that stable Bluetooth tethering should generally be achievable and a good solution if Hammerhead improves support for it. Until then, unfortunately, I cannot reliably use the device for my needs.

Cheers, Felix