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Topic: pull-up resistors for the I2C connection (Read 1 time) previous topic - next topic


When connecting multiple I2C devices/slaves to the Arduino do I need pull-up resistors at each slave or is one set of pull-up resistors enough. When I look a different examples I see both setups.



One single set of pull-ups are what is called for.



1 set of resistors is probably adequate, however, the value of the Rs will be determined
by how many devices are on the buss, and how long the wires are. This is because all those
devices and longer wires increase the total capacitance on the buss, so the risetimes of
the signals will increase [simple first-order RC charging]. If this gets too long, buss
operation will become irratic.

Whereas you usually see 4.7K - 10K pullup values mentioned, 2.7K is probably a better
choice for the situation mentioned above.


Thanks, most devices are not far way (max 20 cm) and some are on the same pcb.

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