Multiple I2C ports

[abouillot]

The I2C implementation on ESP8266 is soft based. It can set the pin to use.
However, I had no success in getting two I2C bus running together. The issue I have is that the I2C device I want to use only have one address and I need two instances of it connected to the ESP. I was planing to open two Wire ports and connect each of the peripheral to one.

Is it possible with today's implementation? Is there any guide on how to achieve this?

[vlast3k]

There shouldn't be any problem, just call Wire.begin(SDA,SCA) before each call to the respective device Though if you expect some callback from the device - it may not work

[tablatronix]

see #2774 , #2607, #2162

[devyte]

Does instancing another Wire object, and initing that to different pins work?

[devyte]

@abouillot did you try any of the comments here?

[devyte]

No feedback in over a month, closing.

[kartom]

This issue should be reopened since i can confirm that creating two instances will not work. The latest call to TwoWire::begin will set the pins used, no matter which object that are used and how they are configured. That since Wire.h is using an underlying twi in a non object oriented way.

void TwoWire::begin(int sda, int scl)
{
    default_sda_pin = sda;
    default_scl_pin = scl;
    twi_init(sda, scl);
    flush();
}

And twi_init uses one global twi object:

void twi_init(unsigned char sda, unsigned char scl)
{
    return twi.init(sda, scl);
}

Every TwoWire object should keep its own twi object, but the twi object is not exposed in the twi.h. Fore some reason the only thing that is exposed is a C wrapper over the object. The twi class itself calls those wrapper functions also, which is kind of strange. (The twi class is a bit of a hack, if you ask me.)

The Wire library looks like it is object oriented, but creating more than one TwoWire objects does not make sense with this implementation. This should be corrected or explained in the documentation.

The best solution imho is to expose the twi class in the twi.h file and redo the implementation of that class so it uses class functions instead of the exposed C-interface. This might however break some compatiblity with the twi.h file (not sure now).

The solution suggested by @vlast3k works but gives rather cluttered code if you like to communicate with devices on both i2c channels since you have to do a Wire.begin before each call to an i2c communication. Most libraries for i2c devices supports initializing their object with a TwoWire object to support multiple i2c channels, wich is necessary if you like to use more devices than there are possible adress configurations for that device. This support is now useless since this implementation prevents multiple TwoWire ojbjects.

[sierramike]

I agree with kartom, the issue should be reopened.
I tried the solution to call the begin() method again each time before having to communicate with another bus, but it's not working, only the first bus is working.
I suppose it is because I need to send a lot of commands in a small amount of time to adjust PWM outputs on multiple PCA9685 cards (one on each bus).

[daneisinger]

@devyte I'm running into this as well.

[devyte]

Please open a new issue, follow the template instructions, explain the problem with the addresses, and reference this issue.
Note: from a quick look at the code, I don't see any practical reason to force a single I2C bus, as long as it is understood that only one bus may work at any given time (sw implementation: timing of one would interfere with timing of the other).

[6leonardo]

Have you solve? can I help? I need more than one i2c on same board?

[Bighoneypot]

@abouillot In case your sensors have the same I2C address, use a TCA9548A multiplexer. I use it and it works great

[6leonardo]

Now it works....it's not very beautiful code but seams to work...
I have tested with 4 gy-bme280... 2 for bus
here the patch in cores/esp8266 I
and in the library Wire
you can put the wire library in local library but for the core I must change the original files
mod_i2c_multi-bus.zip
I attach the code for test the 4 gy-bme280
gy-bme280.ino.zip

[6leonardo]

@abouillot In case your sensors have the same I2C address, use a TCA9548A multiplexer. I use it and it works great

comunque grazie.... mi sa che è la soluzione piu pulita visto che se aggiornano la release perdo tutto....