I have 2 devices that will use the I2C bus talking to an UNO. I understand that I need 1 set of Pullup resistors between the SDA/SCL lines and VCC.
My problem is the 2 devices have different supply voltages. One is an LCD display that only has 3.3v supply and the other is ADS1114 A-D converter that will read a sensor powered off 5v, so I intended to use a 5V supply for this part.
Can these 2 communicate on the same I2C bus?
Where do I connect the pullup resistors to? 5v or 3.3v?
Any help would be appreciated.
Yes the I2C bus (via the two pull-up resistors) can only work at one voltage, suitable to the devices that wire to the I2C bus although there may be I2C slave devices that run at 3.3vdc Vcc power but are '5 volt toleration' on their two I2C I/O pins. As you may already know the ADS1114 chip will work at 3.3vdc or 5vdc.
The fact that you have a sensor that requires +5vdc is not a show stopper by itself but rather what is the signal measurement range that the sensor outputs to the ADS1114 input pins? If it's 3.3vdc or less not a problem. If it can output up to +5vdc then maybe you could just use a two resistor voltage divider to knock down the maximum sensor output (say /2) and then in your sketch software just un-divide it with a simple x2 of the measurement value returned by the ADS chip.