Installation & Support

1. Choose mounting location (near taillights or under dash)
2. Identify switched 12V power source (must turn off with ignition)
3. Locate vehicle's brake/turn signal wires (left and right)
4. Plan wire routing to taillights

1. Select secure mounting location away from heat sources
2. Mark mounting holes using BTsplitter as template
3. Drill pilot holes for M6 or 1/4" fasteners
4. Secure unit with provided mounting hardware

1. Red wire: Connect to switched 12V source (accessory circuit, not constant power)
2. Black wire: Connect to chassis ground or battery negative
3. Verify connections with multimeter before proceeding

1. White wire with black stripes: Connect to left turn signal/brake combined wire
2. White wire: Connect to right turn signal/brake combined wire
3. These inputs are isolated via PC817 optocouplers
4. Inputs are active-LOW (12V when turn signal is active)

1. Green wire: Connect to left turn signal LED (amber)
2. Blue wire: Connect to right turn signal LED (amber)
3. Yellow wire: Connect to brake/stop lights (red - can drive left, center, and right brake lights)
4. Outputs are active-HIGH (HIGH = LED ON)
5. Each output can handle 23A continuous current

1. Reconnect vehicle battery
2. Turn on ignition (BTsplitter powers up)
3. Test left turn signal → Left output should activate
4. Test right turn signal → Right output should activate
5. Press brake pedal → Brake output should activate, turn signals OFF
6. Release brake → Brake stays on for 2 seconds (persistence timer)
7. Test turn signal during brake persistence → Turn signal blinks through

1. Verify all connections are secure
2. Use electrical tape or heat shrink on all connections
3. Route and secure wires away from moving parts and heat
4. Double-check all functions work correctly
5. Close enclosure and tidy up installation

Problem: No Outputs at All

Possible Causes:

• No power to BTsplitter
• Bad ground connection
• Faulty power wire connection

Solutions:

1. Use multimeter to verify 12V at red wire with ignition ON
2. Check ground connection - should read 0V to chassis
3. Verify power source turns off with ignition
4. Connect USB and check Serial Monitor for debug output

Problem: Outputs Always On

Possible Causes:

• Input wires swapped or shorted
• Incorrect output logic (should be active-HIGH)

Solutions:

1. Disconnect input wires and test - outputs should go OFF
2. Check for shorts between input wires
3. Verify input connections to correct white wires
4. Use Serial Monitor to observe input states

Problem: Turn Signals Not Working

Possible Causes:

• Input not connected to vehicle turn signal
• PC817 optocoupler issue
• Incorrect input polarity

Solutions:

1. Verify 12V present at input wires when turn signal active
2. Check PC817 current limiting resistors (should be 1KΩ)
3. Use Serial Monitor to verify inputs are being detected
4. Test with multimeter: input should be HIGH (12V) when off, LOW (0V) when turn signal active

Problem: Erratic Behavior / Flickering

Possible Causes:

• Electrical noise in vehicle system
• Poor ground connection
• Inadequate debouncing for vehicle's electrical system

Solutions:

1. Improve ground connection - use shorter wire to chassis
2. Move BTsplitter away from sources of electrical noise (alternator, ignition coils)
3. Increase DEBOUNCE_DELAY in firmware (default 50ms, try 100ms)
4. Add noise filtering capacitors if needed

Problem: Brake Light Not Working

Possible Causes:

• Output wire not connected
• Both inputs not activating simultaneously
• Timer mode preventing brake activation

Solutions:

1. Verify yellow wire connected to brake light
2. Check that BOTH turn signal inputs activate when brake pressed
3. Use Serial Monitor to verify "BRAKE ON" state is detected
4. Test brake light output with multimeter (should be 12V when active)

• Arduino IDE or Arduino CLI installed
• ESP32 board support package
• USB cable (USB-C to USB-A, included)
• Latest firmware from GitHub repository

1. Download latest .ino file from GitHub
2. Open file in Arduino IDE
3. Select board: Tools → Board → ESP32 Arduino → XIAO_ESP32C3
4. Connect BTsplitter via USB
5. Select port: Tools → Port → [your port]
6. Click Upload button (arrow icon)
7. Wait for "Done uploading" message
8. Open Serial Monitor (115200 baud) to verify new version

# Compile firmware
arduino-cli compile --fqbn esp32:esp32:XIAO_ESP32C3 turnsignal-brakelight-converter.ino

# Upload to BTsplitter
arduino-cli upload -p /dev/cu.usbmodem5101 --fqbn esp32:esp32:XIAO_ESP32C3 turnsignal-brakelight-converter.ino

# Monitor serial output
arduino-cli monitor -p /dev/cu.usbmodem5101 -c baudrate=115200
                    

Can I adjust the brake persistence time?

Yes! The 2-second brake persistence timer is configurable in firmware. Edit the TIMER_DURATION constant (default 2000ms) and upload updated firmware via USB.

Will this drain my battery?

No, if you use switched 12V power as instructed. BTsplitter draws ~100mA when powered, so it MUST connect to a switched source that turns off with your ignition. Never connect to constant/always-on power.

Can I use this with LED and incandescent bulbs?

Absolutely! IRF9540 MOSFETs handle 23A continuous per channel - more than enough for LEDs (typically 50-500mA) and incandescent bulbs (1-2A). You could even drive multiple LED strips per output.

What if my vehicle has more than two brake/turn wires?

BTsplitter is designed for vehicles with two-wire combined brake/turn systems (left and right). If your vehicle already has separate brake and turn signal wires, you don't need a splitter at all!

How do I enable WiFi/Bluetooth features?

The ESP32-C3 has WiFi and Bluetooth hardware, but v1.0 firmware doesn't use them yet. Future firmware updates may add remote monitoring, configuration apps, or integration features. Watch GitHub for updates.

Can I modify the firmware myself?

Yes! BTsplitter uses open-source firmware on GitHub. You can modify timing parameters, add features, or customize behavior. The Arduino platform makes it accessible to anyone with basic C++ knowledge.

What's the difference between this and passive splitters?

Passive splitters use simple diode logic with no timing control, debouncing, or programmability. BTsplitter's microcontroller-based design provides intelligent features like brake persistence, noise immunity, serial debugging, and firmware updates. See our detailed comparison page.