wiring i2c bus

I2C: two shared lines with pull-ups

Wire SDA and SCL for compatible sensors on a short local bus.

Applies to: Ordinary open-drain I2C. Connector-branded systems still require their own pinout and voltage check.

When to use it

Connecting addressed peripherals while using few MCU pins.

Why it works this way

Devices share data and clock lines and release them high through pull-up resistors.

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Connection reference

Signal	Connection	Purpose
SDA	SDA on each device	Bidirectional data
SCL	SCL on each device	Clock; a target may stretch it
GND	Common reference	Non-isolated example
Pull-up rail	Compatible with every I/O	Not automatically the module power input

Make the connection

1. Check addresses for collisions and configure the documented bus speed.
2. Determine the total pull-up resistance from all attached boards.
3. Choose resistance using rise-time, capacitance and sink-current limits; 4.7 kohm is not universal.

Check before powering

• A 5 V pull-up can damage a non-tolerant 3.3 V input.
• Do not cross SDA and SCL. A detected address alone does not prove the correct device or power configuration.

Matching module references

This is a general interface guide; match your own hardware documentation.

Sources & review

Source documents inspected; independent electrical and bench review pending. Reviewed 2026-09-27.

• NXP: I2C specification, UM10204 — SDA/SCL, open-drain bus, addressing and pull-up sizing; checked 2026-09-27

Original writing and diagram by Kal / Valleytech Solutions, CC BY 4.0. Manufacturer artwork and documentation retain their own rights.

CC BY 4.0 · SHA-256: a7b801ab586b24a37d9650a55c6f8fcb29dd7ae65d3d572c80e040b30eff0dce

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