I2C + analog reference

the problem is to connect arduino uno with LCD module(I2C) + LM35 at sametime

I couldn't find any material about working with I2C + analog reference (internal). I am wondering if when it has been set analog reference internal, the I2C communication (A4, A5 pins )stays at 5V, or turns into 1.1V, or worse, I can't do that procedure.

I have bought this leveler. I am aking that question for avoiding any further equipment damage. http://www.ebay.com/itm/221215198834?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649

Analog pins can be used as digital pins. That is how I2C works. Analog-pins-as-digital pins are not affected by the analog reference value, since they are not involved with the ADC at all.

PaulS: Analog pins can be used as digital pins. That is how I2C works. Analog-pins-as-digital pins are not affected by the analog reference value, since they are not involved with the ADC at all.

Thanks PaulS! another question, if I have 2 devices 5.0V and 3.3V(my power supply is external) , do I really need a logic level converter for the I2C output signals?

I believe that the SPI signals will be +5v on a five-volt Arduino. Your 3.3v device probably is not designed to accept voltages above 3.3v, so I think you will need a level shifter, yes.

joshuabardwell: I believe that the SPI signals will be +5v on a five-volt Arduino. Your 3.3v device probably is not designed to accept voltages above 3.3v, so I think you will need a level shifter, yes.

it's make sense Joshua. yes, that device is upper limited at 3.3V, so I will use a shifter. thanks!

Rafaelmec2013: do I really need a logic level converter for the I2C output signals?

I2C signals are open collector. The TWI library does enable the internal pull-ups but you can modify it to disable them. Then use external pull-up resistors to 3V3.

joshuabardwell: I believe that the SPI signals will be +5v on a five-volt Arduino.

Okay well that's SPI and the question is about I2C. They have nothing in common.

[quote author=James C4S link=topic=191653.msg1417526#msg1417526 date=1381037218] I2C signals are open collector. The TWI library does enable the internal pull-ups but you can modify it to disable them. Then use external pull-up resistors to 3V3. [/quote]

That's really interesting, and I'd never heard of that approach before.

joshuabardwell: [quote author=James C4S link=topic=191653.msg1417526#msg1417526 date=1381037218] I2C signals are open collector. The TWI library does enable the internal pull-ups but you can modify it to disable them. Then use external pull-up resistors to 3V3.

That's really interesting, and I'd never heard of that approach before. [/quote]

The internal pullups are so weak (about 30k) that they can be ignored. Just add 4k7 external pullups to 3V3 and it'll interface directly to 3.3V I2C chips. The combined effect is to pull up to 3.5V which is not a problem for 3.3V CMOS chips.