Adafruit
Adafruit LTC4311 I2C Extender / Active Terminator - STEMMA QT / Qwiic
The Adafruit LTC4311 Active Terminator solves a common I2C problem: running long cables. Standard I2C is designed for short PCB-level connections, but cable ...
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The Adafruit LTC4311 Active Terminator solves a common I2C problem: running long cables. Standard I2C is designed for short PCB-level connections, but cable capacitance and resistance degrade signals over distance. The LTC4311 watches the SDA and SCL lines and actively boosts pull-up current, restoring clean square-wave signals even over multi-metre cables.
Simply plug this board into your I2C bus at the start of the chain — no firmware, software, or configuration needed. In testing, it ran a 400 kHz OLED over 3 metres of phone wire with ease, and even drove a BME680 sensor over 30 metres of Ethernet cable at 100 kHz (~3000 pF round trip).
Key Features
- Active I2C Termination – Boosts pull-up current on SDA and SCL for clean signal edges over long cables
- Wide Voltage Range – Works with any bus voltage from 1.6 V to 5.5 V
- Up to 400 kHz – Supports standard and fast I2C clock speeds
- Cable Capacitance up to 4000 pF – Handles very long cable runs
- Zero Configuration – No firmware, software, or resistor tuning required; just plug in and go
- STEMMA QT / Qwiic – Solderless I2C connectors on both sides for easy daisy-chaining
Ideal For
- Running I2C sensors over long cables (1–30+ metres)
- Fixing unreliable I2C communication on extended buses
- Remote sensor installations connected by phone wire or Ethernet cable
- Any I2C project where cable capacitance is degrading signal quality
Package Contents
- 1× Adafruit LTC4311 I2C Extender / Active Terminator (STEMMA QT)
Resources
Jargon buster
Plain-language definitions for the technical terms used above.
- BME680
- The BME680 is a Bosch environmental sensor chip that measures temperature, humidity, air pressure and a gas signal used to gauge air quality. The part number tells you a device is built around that specific all-in-one sensor, so you can check its library support, accuracy and datasheet details.
- capacitance
- Capacitance is the amount of electrical charge a capacitor can store, usually measured in farads such as uF. Choosing the right capacitance value matters because it affects how well a circuit filters power, handles timing, or stores short bursts of energy.
- I2C
- I2C is a two-wire communication bus used by many sensors and small modules. It matters because several I2C devices can share the same two wires, but each device needs a compatible address and your controller must support I2C.
- OLED
- OLED stands for organic light-emitting diode, a display type where each pixel produces its own light. It matters because OLED screens are thin, high-contrast and easy to read for small status displays, but they can be more sensitive to image burn-in than some other display types.
- PCB
- A printed circuit board (PCB) is a board, usually rigid, with etched copper tracks that connect electronic components together without loose wiring. Components are mounted on the board and signals route between them through the copper layout.
- Qwiic
- Qwiic is a plug-in connector system for I2C devices that uses small 4-pin cables, so you can connect compatible sensors without soldering. It matters because your controller or adapter also needs Qwiic, or you will need a cable or breakout to wire it up.
- STEMMA
- A plug-and-cable connection system used on some maker electronics boards to make wiring simpler. If a product uses STEMMA, you need the matching cable or connector type to plug it in without soldering.
- STEMMA QT
- A small plug-in connector system for I2C boards that lets you connect compatible sensors and controllers without soldering. It matters because it can make wiring faster and less error-prone, especially when adding several small modules to a project.
introducing adafruit stemma qt
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Resources & Downloads
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Related Tutorials
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