ESP8266 Community Forum

- Wed May 20, 2015 2:44 pm #17998 I'm hoping to connect several devices over I2C like the BMP180. I'm using the driver at https://github.com/reaper7/esp8266_i2c_bmp180 Typically what needs to be done to have several I2C devices hooked up? Each would have to use a unique set of pins, right?

Thanks

- Wed May 20, 2015 2:58 pm #18000 Right ! Since this device doesn't have address pins, you can only hook 1 device per I2C bus.

- Wed May 20, 2015 4:29 pm #18004 Then why do they call it a "bus"? What is the "device address" used for?

- Wed May 20, 2015 5:36 pm #18007 I2C devices such EEPROM usually have 3 address pins, so 8 EEPROM can be attached on the same bus along with some others such ADC, DAC or Temp sensors, the effective addresses are those 3 pins merged with hardcoded manufacturer base address. The whole bus has 128 devices address space. But the BMP180 doesn't have those 3 pins, so it use only the hardcoded manufacturer base address which is according to specs at 0x77 (when shifted to add the R/W, it give 0xEF for read and 0xEE for write).
So, only 1 BMP180 per Bus... There is maybe some other sensors with address pins, but I didn't search ...

EDIT : in a second thought, why do you wish to have several BMP180, they will all measure the same barometric pressure ...
If you means other sensors such Temp and Humidity, there won't be any problems having them on the same bus, as long as hardcoded manufacturer base addresses are not conflicting.