Mixed Voltages and level converters help please

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rizzy_dascal

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Hi,

I am about to start a project that uses a pic18f24J11 chip which is 3.3v, also I have a sim800L gsm board that is 3.3v and I believe I can connect this board directly to the micro-controller pins, however I have a 5v i2c LCD display now will the i2c line need some sort of level shifter because the display is 5v and the chip is 3.3v ?

Thanks
Rizzy
 

If you're only driving the i2c lines to the LCD (not receiving 5V signals) then 3.3V CMOS logic outputs are high enough to be seen as logic 1 in 5V TTL logic, which has a 2V Vih.

This link shows various voltage levels for the 5V logic families, you'll notice if you are in the left most column and the LCD requires straight CMOS then it won't work and you'll need actual level translators.
 

Hi,

There are many I2C devices that run with 5V supply and can communicate with 3.3V signals .
--> The datasheet will tell you.

Klaus
 

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