Stelo → Karoo 2 Direct BLE Setup

This guide explains how to set up a direct Bluetooth connection between a Dexcom Stelo CGM sensor and a Hammerhead Karoo 2 cycling computer using a modified xDrip build. No phone is needed during rides.

---

What You Need

• Hammerhead Karoo 2
• Dexcom Stelo sensor
• Windows PC with ADB installed
• USB cable
• The following files in C:\Android\platform-tools\ (available in the GitHub repository):
  • xDrip-working.apk
  • working_prefs.xml

For ADB installation and APK deployment setup, follow this guide: https://www.dcrainmaker.com/2021/02/how-to-sideload-android-apps-on-your-hammerhead-karoo-1-karoo-2.html

---

Step 1 — Enable Developer Mode on Karoo

1. On the Karoo go to Settings → About
2. Tap Build Number 7 times
3. Go to Settings → Developer Options
4. Enable USB Debugging
5. Connect the Karoo to your PC via USB
6. Accept the USB debugging prompt on the Karoo screen

---

Step 2 — Verify ADB Connection

adb devices

You should see something like KAROO20XXXXXXX device. If it says unauthorized check the Karoo screen and tap Allow.

---

Step 3 — Install xDrip on Karoo

Uninstall any existing xDrip first:

adb uninstall com.eveningoutpost.dexdrip

Then install:

adb install xDrip-working.apk

---

Step 4 — Push Prefs to Karoo

Open xDrip on the Karoo and when prompted allow all permissions. Then go to Menu → Settings → Transmitter ID and enter your 4-character Stelo transmitter ID printed on the sensor applicator. Wait 15 seconds for xDrip to fully initialize, then run these commands without closing xDrip:

adb push working_prefs.xml /data/local/tmp/working_prefs.xml
adb shell run-as com.eveningoutpost.dexdrip cp /data/local/tmp/working_prefs.xml /data/data/com.eveningoutpost.dexdrip/shared_prefs/com.eveningoutpost.dexdrip_preferences.xml
adb shell run-as com.eveningoutpost.dexdrip chmod 444 /data/data/com.eveningoutpost.dexdrip/shared_prefs/com.eveningoutpost.dexdrip_preferences.xml
adb shell am force-stop com.eveningoutpost.dexdrip
adb shell am start -n com.eveningoutpost.dexdrip/.Home

chmod 444 locks the file as read-only so xDrip cannot overwrite the credentials on restart.

---

Step 5 — Connect to Stelo

1. In xDrip go to Menu → System Status → Dex Status
2. Tap Restart Collector
3. Brain State should move from Scanning to Authorizing to Connected
4. First glucose reading arrives within 5 minutes

---

Step 6 — Restore Write Permissions

After confirming the connection is working:

adb shell run-as com.eveningoutpost.dexdrip chmod 644 /data/data/com.eveningoutpost.dexdrip/shared_prefs/com.eveningoutpost.dexdrip_preferences.xml

---

ConneXX

ConneXX extends the Hammerhead Karoo sample app with two features: partner metric sharing over Bluetooth Classic, and live blood glucose display from a Dexcom Stelo CGM sensor.

---

Data Fields

Field	Description
User HR / Power / Speed	Your own sensor data routed through ConneXX
Partner HR / Power / Speed	Your partner's live metrics over Bluetooth
Partner % of FTP	Partner power as a percentage of their FTP
Partner % of Max HR	Partner heart rate as a percentage of their max HR
User Glucose	Live blood glucose from Dexcom Stelo with trend arrow

Glucose Display

Display	Meaning
145 →	Stable
145 ↑	Rising
145 ↑↑	Rising rapidly
145 ↓	Falling
145 ↓↓	Falling rapidly
---	No data / sensor disconnected

Adding ConneXX Fields to Your Ride Profile

1. On the Karoo go to Settings → Profiles
2. Select the profile you ride with and tap Edit
3. Tap any data field slot and select Add Field
4. Scroll the list to find the ConneXX fields and tap one to add it

For a visual walkthrough of the profile editor, see the Karoo Support Documentation: https://support.hammerhead.io/hc/en-us/articles/4595942669979-Karoo-2-Customising-Profiles

---

Building & Installing the ConneXX APK

Step 1 — Enable Developer Mode on Karoo

1. On the Karoo go to Settings → About
2. Tap Build Number 7 times
3. Go to Settings → Developer Options and enable USB Debugging
4. Connect the Karoo to your PC via USB and accept the USB debugging prompt on the Karoo screen

Step 2 — Verify ADB Connection

cd C:\Android\platform-tools adb devices

You should see KAROO20XXXXXXX device. If it says unauthorized, tap Allow on the Karoo screen.

Step 3 — Build the APK

From Android Studio: Click Run with your Karoo connected — it builds and installs automatically.

From the command line: ./gradlew assembleDebug

APK output path: sample/build/outputs/apk/debug/sample-debug.apk

Install directly via Gradle: ./gradlew installDebug

Or install manually via ADB: adb install -r sample/build/outputs/apk/debug/sample-debug.apk

Once installed, ConneXX registers all data fields automatically when a ride starts.

---

Before & After Every Ride

Before: Force stop xDrip on your phone via Settings → Apps → xDrip → Force Stop. The Stelo can only bond to one device at a time — the phone must release before the Karoo can connect.

After: Restart xDrip on your phone. It will re-bond with the Stelo automatically on the next advertisement cycle.

---

Troubleshooting

Problem	Fix
run-as: package not debuggable	Wrong APK installed — uninstall and reinstall xDrip-Karoo-prod-debug.apk
keks_p1 FAILED during injection	xDrip prefs file not created yet — open xDrip and wait 15 seconds first
Missing QR code after injection	Injection didn't take — repeat Step 4
Scanning errors 4+	Phone xDrip still running — force stop it
Mismatch error	Wrong transmitter ID — check the 4-char ID on the sensor applicator
Connection drops after first reading	Restore write permissions (Step 6) then restart collector

---

How It Works

The Stelo uses a certificate-based BLE authentication protocol internally called KEKS. During initial phone pairing, three certificate parts (keks_p1, keks_p2, keks_p3) are stored in xDrip's preferences. Without these the Karoo shows "Missing QR code" and cannot connect.

The injection script writes these certificates directly into xDrip's preferences file on the Karoo, giving it everything it needs to authenticate with the Stelo.