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I2C Scan Test

A lot of sensors, displays, and devices can connect over I2C. I2C is a 2-wire 'bus' that

allows multiple devices to all connect on one set of pins so it's very convenient for

wiring!

When using your board, you'll probably want to connect up I2C devices, and it can be

a little tricky the first time. The best way to debug I2C is go through a checklist and

then perform an I2C scan

Common I2C Connectivity Issues

Have you connected four wires (at a minimum) for each I2C device? Power the

device with whatever is the logic level of your microcontroller board (probably

3.3V), then a ground wire, and a SCL clock wire, and and a SDA data wire.

If you're using a STEMMA QT board - check if the power LED is lit. It's usually a

green LED to the left side of the board.

Does the STEMMA QT/I2C port have switchable power or pullups? To reduce

power, some boards have the ability to cut power to I2C devices or the pullup

resistors. Check the documentation if you have to do something special to turn

on the power or pullups.

If you are using a DIY I2C device, do you have pullup resistors? Many boards do

not have pullup resistors built in and they are required! We suggest any common

2.2K to 10K resistors. You'll need two: one each connects from SDA to positive

power, and SCL to positive power. Again, positive power (a.k.a VCC, VDD or V+)

is often 3.3V

Do you have an address collision? You can only have one board per address. So

you cannot, say, connect two AHT20's to one I2C port because they have the

same address and will interfere. Check the sensor or documentation for the

address. Sometimes there are ways to adjust the address.

Does your board have multiple I2C ports? Historically, boards only came with

one. But nowadays you can have two or even three! This can help solve the

"hey, but what if I want two devices with the same address" problem: just put

one on each bus.

Are you hot-plugging devices? I2C does not support dynamic re-connection, you

cannot connect and disconnect sensors as you please. They should all be

connected on boot and not change. (Only exception is if you're using a hot-plug

assistant but that'll cost you()).

Are you keeping the total bus length reasonable? I2C was designed for maybe

6" max length. We like to push that with plug-n-play cables, but really please

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Adafruit ESP32-S3 User Manual

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