I have an I2C design question.
I currently use an I2C connection with 4.5 m cables (the system is initially planned to use 1.5 m cables). It works surprisingly well so far. Recently I had short data loss.
I have 2 questions:
I2C is a communication protocol designed for communications within a PCB assembly. It was not designed to be used over long cables*.
"I2C ..., is a synchronous, multi-master/multi-slave (controller/target), packet switched, single-ended, serial communication bus... It is widely used for attaching lower-speed peripheral ICs to processors and microcontrollers in short-distance, intra-board communication." Source
Can the use of abnormally long I2C cable damage the electronic card
Yes. Due to the wires acting as antennas picking up 50 Hz and high-frequency noise.
What is the most probable cause of these data losses?
Interference and badly misshapen waveshapes.
(*) Despite that, it has been included in some carefully designed cable interfaces.
When properly designed and engineered, I2C can go many meters over a cable succesfully, as is proven by billions of cables used in homes, offices, meeting rooms and classrooms - for example each and every modern analog VGA, DVI and HDMI cables successfully use I2C for negotiating supported resolutions between source devices such as computers, video disc players, gaming consoles and displays such as TVs, monitors and projectors.
So I2C is really nothing more than a specific kind of open-collector bus and open-collector buses have been in general used over cables just fine.
Yes. Always the case with long wires. Any nearby source of disturbance may affect the long wires. ESD, nearby voltage or current surges, RF signals from antennas. Lightning, huge motors, arc welding in a factory, etc. are always possible. Even just flipping a light switch in your home may cause a bad system to lock up.
Any glitch on the bus can cause any problem. Either your I2C hardware gets into a state it cannot handle or your software does not handle errors that may happen.
If you are worried about noise coming down the cable and damaging your electronics, or data loss due to misshapen wave forms, you can place an I2C buffer at either end of the cable. Something like the Texas Instruments TCA4307 https://www.ti.com/product/TCA4307
Here is an example from page 13 of the data sheet for a long distance bus https://www.ti.com/lit/ds/symlink/tca4307.pdf
Note that "long distance" isn't defined in the datasheet. It might be because the output properties depend on cable capacitance and voltage levels.
The buffers have many nice features, but for your application, the buffers do two things:
As an example, we had no problems communicating between a Raspberry Pi 4B and a Maxim Integrated MAX7300 over 1 m twisted pair cable. When we went to 2 m cable, approximately 5 % of our messages sent were received incorrectly (or not at all). After adding the TCA4307 buffers to either end of the cable, we sent 500,000 messages without error.
The risk of damage comes from ESD (static discharge) and EMF (inductive coupling from nearby circuits).
You can guard in two ways:
You will still experience data loss during ESD/EMF events, but will be able to avoid catastrophic damage. Another source of data errors will be the difference in ground potential between the two devices. This difference is dynamic, ie, it changes as the load at the two endpoints changes; suppose you turn on a vacuum cleaner or microwave plugged into the same or nearby outlet as one of the two devices. The local ground level will move up by some non-negligible amount.
To minimize data loss, you have two possibilities:
Update to caution about "long range drivers": Other answers suggest use of buffers or drivers meant for "long range", but you should mind whether the two sides of the bus have a common ground or not. Such buffers are suitable in applications where both ends of the bus reference the same ground, like automotive or instrumentation, but not in residential or commercial applications where each end uses a separate power supply, and thus a different ground reference.
