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mahmoud899

Stellaris interfacing with LCD

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Hello,

 

I have a Stellaris Launchpad LM4F120XL Board and I am trying to interface with an 16x2 LCD. My LCD requires 5V and my Stellaris Launchpad has 3.3V output power pin. I have 2 questions,

 

1) Would it be alright if I connected the LCD to an external 5V supply and connected the data pins (D0-D7) to the Stellaris Launchpad GPIOs or do I have to have an LCD that operates on 3.3V supply?

 

2) Will it work if I connected the LCD to the 3.3V output power pin of the Stellaris Launchpad and connected the data pins (D0-D7) to the Stellaris Launchpad GPIOs ?

 

Thank You

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1) No. because HIGH level from the Stellaris could be considered as LOW by the LCD, and HIGH level from the LCD could damage the Stellaris. So take instead a screen working at 3.3V.

 

2) Usually, LCD doesn't require much power except for the backlight. Most screens have a separate power input for backlight. You need to know how much power the screen requires and check in the Stellaris LaunchPad User Guide that the voltage regulator can supply it.

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Aren't some of the pins on the Stellaris LP 5volt tolerant in input config?  (i.e. they would not be damaged by a 5volt signal coming in to them).

(See e.g. page 59 of LM4F120H5QR manual.)

(You still don't want to provide the Stellaris with 5volts on the power pins.  And they are definitely limited on current sinking.)

Check the documentation to be sure (e.g. which pins).

 

However I would probably first try using a 3.3v supply for the LCD.

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Since the communication between the two devices is mostly unidirectional, you may want to consider level shifting the data lines either with a dedicated level shifting IC or a transistor.  Also, to make the circuit a little simpler in terms of level shifting circuitry you may want to use the 4 bit data configuration on the LCD rather than 8 bit.

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Go for a Nokia 5110 display.

 

It is really cheap and there are many libraries available for it.

 

It features 84 x 48 pixels = 15 characters x 6 lines with 6 x 8 pixels per character, so you'll learn graphics too.

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