jerabaul29
commented
3 years ago Have you actually encountered this I2C problem in practice? (just being curious :) ).
It seems that there is an easy fix: the issue you link to has actually been closed in favor of issue https://github.com/arduino/ArduinoCore-avr/issues/42 which implemented a fix. For backwards compatibility reasons or something like this it is not enabled by default I think (see discussion https://github.com/arduino/reference-en/issues/895 ). I will add it to the program to "robustify" things :) .
I will change the I2C frequency then, to be on the safe side :) .
jvoermans
@jerabaul29 We probs need a safety net in case an I2C sensor has a defect and causes the arduino to hang. It is something in the Wire library, but there hasn't really been a solid solution to this: https://github.com/arduino/Arduino/issues/1476
It doesn't always occur. If the complete sensor is gone, or the data and/or clock line are gone it just simply cannot find the sensor. The problem actually occurs when the VCC and/or GND lines are disconnected. In general, this is unlikely to happen. If the sensor is broken, it is most likely that the sensor won't respond at all, so that is not an issue. If the sensor is ripped off completely, that is also not an issue as all lines will be disconnected. Nevertheless, sounds a bit uncomfortable to rely on simply 'unlikely to happen'.
So I guess there are two approaches to prevent the arduino from potential freezing: 1) initiate regularly if the sensor is present. If not present, skip this sensor and go to the next. If a sensor fails while measuring and freezes the arduino, this is likely to happen only once and the watchdog can just reset the whole thing. 2) some kind of 'sub-watchdog' which, rather than resetting the arduino, cancels the task of the sensor reading and continues the loop.
Regarding the first, the following library works quite well to identify if a sensor is present, however, problem remains when disconnecting only GND and/or VCC. It is an alternative library to the Wire library, but can be cut down to just the function that is needed to check if sensor is present (like an I2C scanner). https://github.com/DSSCircuits/I2C-Master-Library
I initially though the watchdog could be used to 'break' a loop rather than resetting the arduino, but apparently this is not possible (break needs to be within a loop and watchdog works parallel not in series as far as I understand?).
Do you have any suggestions? Also, what I2C clock speed are we using? I think it is best to drop it down to say 50-100kHz or even lower if possible. I2C doesn't like long cables, but general advice is that it can still work on longer cables when clock speed is reduced. I tried the Multispeed I2C Scanner with the temperature sensor and it is able to go over a 5m long cat6 cable at 400kHz without problems, but perhaps better to drop it down as much as possible to prevent problems with signal glitches and thus potential freezing....