HOWTO using the I2C bus:

[TrDA-hab]

About I²C (I2C, IIC) bus:

• Tasmota - Supported I²C devices
• Wikipedia
• Sparkfun - I²C Bus tutorial
• NodeMCU - I²C Bus tutorial
• Wemos - pin map
• NXP - I²C bus specification
• TI - I²C Bus Pull-up resistor calculation
• Online - I²C Bus Pull-up resistor calculator

0.

About using the I²C bus:

• the maximum allowable I²C bus capacitance is 400 pF, the bus length does NOT matter.
• it is not allowed to use devices with the same addresses.
• the maximum number of devices on the I²C bus is no more than 128 pcs. Addresses from 0 to 127, one for "master" and others for "slave". Excluding reserved addresses (1).
• ready-made I²C modules, already have pull-up resistors, and you should not worry.
• what type of pull-up resistors should we choose for "handmade" device? It depends on many factors, but to be on the safe side anything between 1.5 kΩ and 14 kΩ (optimal 4.7 kΩ). The more devices are connected to the I²C bus the smaller(!) has to be the resistor.
• the ESP8266(ESP32) activates its internal pull-up resistors for SDA and SCL, so you usually don't need to install external ones (they are required for slaves).
• if you need a "longer" I²C bus, you must use a repeater (2).
• if you need more devices with the same address, you must use a multiplexer (3).
• if it is necessary to logically match the levels, you must use alevel translator (4).
• if you need to connect several sensors, you must use I²C extender (5).
• I²C bus allows connecting (hot-swappable) modules.
• for the I²C bus, you can use the (Rx and Tx) of your ESP8266.
• the ESP8266 chip does not have hardware I²C, so module uses software I²C driver. It can be set up on any GPIO pins. The recommended convention for the I²C bus is used to select the GPIO pins - SDA on GPIO4 (D2) and SCL on GPIO5 (D1). For ESP32 recommend using GPIO pins - SDA on GPIO21 and SCL on GPIO22.
• if you have done all the necessary settings and connections correctly, then after starting (or restarting) the ESP you will see all the found I²C devices.
  00:00:03.974 I2C: BME280 found at 0x76
00:00:03.985 I2C: BME280 found at 0x77
00:00:03.987 I2C: BH1750 found at 0x23
00:00:03.988 I2C: INA219 found at 0x40
00:00:03.989 I2C: INA219 found at 0x41
00:00:03.990 I2C: INA219 found at 0x44
• also using the i2cscan command you can see the detected I²C devices.
  21:11:38.107 CMD: i2cscan
21:11:38.129 MQT: stat/Sonoff_Baro_1/RESULT = {"I2CScan":"Device(s) found at 0x23 0x40 0x41 0x44 0x76 0x77"}
• you can also enable and disable I2C devices using the I2cDriver command (they are always enabled by default). More details (here).
  21:12:52.527 CMD: I2cDriver
21:12:52.534 MQT: stat/Sonoff_Baro_1/RESULT = {"I2CDriver":"3,4,5,7,10,11,14,47"}
21:13:45.850 CMD: I2cDriver14 0
21:13:45.857 MQT: stat/Sonoff_Baro_1/RESULT = {"I2CDriver":"3,4,5,7,10,11,!14,47"}

1.

Reserved I²C addresses:

• 0x00 - Reserved - General Call Address.
• 0x01 - Reserved for CBUS Compatibility.
• 0x02 - Reserved for I²C-compatible Bus Variants.
• 0x03 - Reserved for Future Use.
• 0x04, 0x05, 0x06, 0x07 - Reserved for Hs-mode Master.
• 0x78, 0x79, 0x7A, 0x7B - Reserved for 10-bit I²C Addressing.
• 0x7C, 0x7D, 0x7E, 0x7F - Reserved for Future Purposes.

2.

If it is necessary to "increase the capacity" of the I²C bus, then it is necessary to use - the PCA9515A repeater:

• no software support required (!).
  https://aliexpress.ru/item/32757561351.html
  https://www.ti.com/lit...pdf?&ts=1589295453250
  https://www.onsemi.com...lateral/PCA9517A-D.PDF

3.

If it is necessary to bypass the same addresses on the I²C bus, then it is necessary to use - TCA9548A multiplexer:

• software support required (!!!), now (02/01/2021) is not supported in Tasmota.
  https://aliexpress.ru/item/4000067621113.html
  https://www.ti.com/lit/ds/symlink/tca9548a.pdf

4.

If it is necessary to logically match the levels (for example 5V and 3.3V), then it is necessary to use - Level Translator PCA9306:

• About logic level

• no software support required (!).
  https://www.ti.com/lit/gpn/PCA9306
  https://www.sparkfun.com/products/15439
  https://aliexpress.ru/item/4000507058874.html
  https://aliexpress.ru/item/32805554320.html

5.

If you need to connect several sensors, you must use - I²C extender:

• no software support required (!).
  https://aliexpress.ru/item/4001116856790.html
  https://aliexpress.ru/item/1005001351911782.html
  https://aliexpress.ru/item/32964147782.html
  https://aliexpress.ru/item/32965171426.html
  https://www.ebay.com/itm/I2C-IIC-Extender-for-Arduino-Sensor-Shield-with-Cable/121200480686

6.

It is possible to combine different options (1+2+3+4).

7.

#UPD 1.
Manufacturer claims up to 100 feet (~ 30 meters) for each PCA9615 controller:
https://learn.sparkfun.com/tutorials/qwiic-differential-i2c-bus-extender-pca9615-hookup-guide
Sell here:
https://aliexpress.ru/item/33018940484.html

#UPD 2.
Here it is generally stated "up to 300 meters" on a twisted pair:
https://www.ebay.com/itm/RJ45-Differential-I2C-Long-Cable-Extender-PCA9600-with-Boost-Converter-Arduino/121765222831
https://www.ebay.com/itm/Differential-I2C-Long-Cable-Extender-PCA9600-with-Boost-Converter-for-Arduino/112580556568

#UPD 3.
The manufacturer claims up to 20 meters if you use two P82B715 controllers:
https://www.ebay.com/itm/I2C-IIC-Active-Long-Cable-Extender-P82B715-Module-for-Arduino-and-Other-MCUs/112292264539

Best regards,
TrDA.

[barbudor]

Thanks.
Little copy/paste error on title 2.

[TrDA-hab]

Thanks, I fixed it quickly !!!!

[elik745i]

Thanks for usefull info!

[sfromis]

An often used convention for selecting GPIO pins is I2C SDA on GPIO4 (D2) and I2C SCL on GPIO5 (D1). While these pins are not "especially great", they do avoid complications with encumbered pins, and at least the Wemos D1 Mini shields using I2C are wired to these pins.

Thus, this tends to be my selection on ESP8266, unless I have reasons to differ. For NodeMCU, I sometimes use a 6-way dupont wire shell (with 4 on the other end) to have an easy plugin matching a large part of the I2C sensors having SDA,SCL,GND,VCC.

[TrDA-hab]

An often used convention for selecting GPIO pins is I2C SDA on GPIO4 (D2) and I2C SCL on GPIO5 (D1). While these pins are not "especially great", they do avoid complications with encumbered pins, and at least the Wemos D1 Mini shields using I2C are wired to these pins.

Thus, this tends to be my selection on ESP8266, unless I have reasons to differ. For NodeMCU, I sometimes use a 6-way dupont wire shell (with 4 on the other end) to have an easy plugin matching a large part of the I2C sensors having SDA,SCL,GND,VCC.

Thanks a lot for your help, I have added the required information.

[grappini]

Is TCA9548A still not supported in tasmota ?

[sfromis]

No, and due to many drivers doing initialization (including the sensor), it it would not be a simple change.

[grappini]

Is there any other way to use 2 sensors with same i2c address in tasmota ?

[sfromis]

Just have two Tasmota devices. Real easy and cheap :-)

Otherwise: No, unless you create a driver in Berry on ESP32 for the sensor on the 2nd I2C bus

[ramanraja]

I am not using I2C, so in my custom build I have commented out the line
//#define USE_I2C
Then why are are following lines mandatory for compiling?

#define I2CDRIVERS_0_31        0xFFFFFFFF          // Enable I2CDriver0  to I2CDriver31
#define I2CDRIVERS_32_63       0xFFFFFFFF          // Enable I2CDriver32 to I2CDriver63
#define I2CDRIVERS_64_95       0xFFFFFFFF          // Enable I2CDriver64 to I2CDriver95

I get a compiler error if I comment out these lines. I am worried that the I2C drivers 0 to 95 will be unnecessarily enabled - at least that is what the comments seem to indicate.

[barbudor]

If I2C is not used, it doesn't matter if those are enabled. It will not changed anything.
These are used to initialized Tasmota settings on 1st run. Tasmota settings must be initialized so these values must exist.
If that bother you, define them to 0.
Note that all customization MUST be done in user_config_override.h and not in any Tasmota files (which includes my_user_config.h)

[sfromis]

If you want a successful compile, never comment out values for features you do not need, only unconfig the features as such. Those #define with a value go into configuring a common settings area, which must have values available, even when not used later.

[ramanraja]

Thanks, my issue can be closed.

[vchrizz]

Thank you very much for this HOWTO.
I could get the BMP280 sensor working on a Shelly1 by flashing tasmota-sensors.bin.gz (because standard recommended release does not seem to have the BMP280 drivers compiled in) and connecting/setting GPIO0 to I2C SCL and GPIO3 to I2C SDA.