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I want to interface my microcontroller (ATmega32) with a 2x16 LCD. I am powering my microcontroller with 3.3V, and I need to use 5V with the LCD. Will be there any problem with that (i.e data signals from the microcontroller to the LCD will have logic 3.3 while VDD and Backlight for the LCD will be powered by 5.0V)

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  • \$\begingroup\$ Verify Voh/Vol, Vih/Vil levels from both Controller and LCD. Some uC pins can handle 5V. \$\endgroup\$ – user19579 Mar 9 '17 at 11:14
  • \$\begingroup\$ READ THE DATASHEETS! (duh) \$\endgroup\$ – Olin Lathrop Mar 9 '17 at 12:08
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Check that:

\$V_{OH-µC}>V_{IH-LCD}\$

\$V_{OL-µC}<V_{IL-LCD}\$

If you're reading data from the LCD too, check:

\$V_{IH-µC}<V_{OH-LCD}\$

\$V_{IL-µC}>V_{OL-LCD}\$

Where :

\$V_{OH}\$ is the High level Output Voltage

\$V_{IH}\$ is the High level Input Voltage

\$V_{OL}\$ is the Low level Output Voltage

\$V_{IL}\$ is the Low level Input Voltage

Make sure to read these value in operating conditions as close to yours as possible. They're typically given in datasheet under different load and supply voltage conditions.

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There is no such thing as too basic a question. To supplement @HatimB's comment, you essentially want to understand what the logic voltage levels are for the input to the LCD. If data is only going from the micro to the LCD, then you just need to make sure that a logic high output of the micro would be sufficient for a logic high of the LCD. Same goes for logic low.

It is likely that the 5V LCD logic expects upwards of 3+ volts for a 'high' and below 1.8 for a 'low'; the microcontroller will try to push the amplitude of VCC of the micro (3.3VDC for you) for the high. This means that you may or may not require a level translator device. There are quite a few cheap/easy ones out there, and Digikey has a great selection. You also may be able to play with the VCC voltage to the micro, going higher than 3.3V while remaining within the operating recommendations of the micro. This would (depending on the controller) enable the logic high to be higher, as many have their high levels relative to VCC.

More likely--the thresholds and hysteresis band (a band that makes the threshold less prone to noise) will be a little different and you should expect a slight delay.

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