TFI2CEXT01 - I²C Bus Extender Documentation

The TFI2CEXT01 is an I²C bus extension module designed to extend the possible total length of the I²C bus on UAVs and drones. The module does not contain any configuration or modifiable firmware. Therefore, this module does not require any setup and can be connected to any I2C bus.


The TFI2CEXT01 I²C bus extender is commercially available from ThunderFly s.r.o. For purchasing, you can:


Data rateUp to 400 kHzDefined by used TCA4307 IC
I²C Connector2x 4-pin JST-GHConnected in parallel, it is possible to extend to 4 JST-GH connectors
Operating and storage temperature-20°C to +40°CLimited by case material
Operational input voltage3.6V to 5.4VPixhawk standard compatible
Mass~2 gPCB
Dimensions15x25x6(10.5) mmOne-sided connectors (10.5 mm with the JST-GH connectors on both sides of PCB)
Weather resistanceIP30Using 3D-printed enclosure


  • Input Power Status LED Indicator
  • Optional Pass-Through I²C Connectors: Allows daisy chaining of different sensors.
  • Bus Segment Isolation: Can disconnect stacked devices.
  • Differentiated Handling of Master and Slave Bus Sides
  • Device Reset Capability: Can reset frozen devices.
  • READY Signal Indication: Shows correct connection of both I²C bus sides.

The two I²C Pixhawk connectors on the bottom and top are directly connected, facilitating easy integration with other I²C devices on existing bus cabling. With dual connectors on both the slave and master sides, the module is also recommended for splitting an existing I²C port into multiple devices.

Device Reset Functionality

The TCA4307 features stuck bus recovery, automatically disconnecting the slave side of the bus from the master if it detects either SDAOUT or SCLOUT low for approximately 40 ms. Once disconnected, the device generates up to 16 pulses on SCLOUT to attempt to reset any device holding the bus low.


Optimal performance is achieved when the TFI2CEXT01A is positioned in the middle of the length between the master and slave devices. This positioning ensures effective active signal amplification for both signaling directions. However, in real-world applications, I²C devices have varying driving capabilities, and I²C signals are often affected by capacitive load or unwanted signal coupling. The TFI2CEXT01A can isolate signals in bus segments, making it ideal for connecting to “problematic” I²C devices closer to the module.

Connection Instructions

Special attention is required for proper connection due to the device reset capability of the TFI2CEXT01A. The connector closer to the LEDs should be connected to the Master device (e.g., autopilot). The opposite connector, farther from the LEDs, should be connected to I²C slaves, such as sensors.

Current version

TFI2CEXT01A: Current version is TFI2CEXT01A