Arduino and 3.3V LCDs

Forum 2005-2010 (read only) Hardware Interfacing
1

Hello,

These are stupid questions from an electronic newbee?

I try to connect this lcd to an arduino 2009? without success :frowning:

the real lcd datasheet is here: http://www.sparkfun.com/datasheets/LCD/ADM1602K-NSW-FBS-3.3v.pdf

Up to now, I connected both power pins and led backlight to 3.3V (following the datasheet)? but I'm wondering what is the output voltage of arduino pins. So the question is: can I use a 3.3V lcd display with an arduino or shall I use 5V displays only?

By the way, can I replace the potentiometer between Vss and V0 by a 15k resistor? (this is for contrast adjust)

Thank you in advance for your help.

Thomas

2

There is nothing in the data sheets to indicate that the inputs are 5V tolerant. So you should only connect it with a 3V3 signal.

You could use the ideas here to use the 5V signal from your Arduino:-
http://www.thebox.myzen.co.uk/Tutorial/Protection.html

but use a 100R resistor in place of the 20R

3

So you mean that arduino outputs are 5V only.

and that the easiest will be to buy another lcd (this time 5V)
(or of course to follow the link you proposed above; actually, I do not really understand why the 100R resistor would drop the voltage from 5 to 3V)

I thought it was 3.3V output with a 5V pull up and was wondering if the pull up can be disabled. But I was not able to find doc on the output voltage: could you help me to find this?

Thanks a lot! Thomas

4

So you mean that arduino outputs are 5V only.

Yes the output is as high as the supply voltage.

I do not really understand why the 100R resistor would drop the voltage from 5 to 3V

It doesn't. It is those catcher diodes that do the limiting, in your case they would go to the 3V3 supply. The go to the supply voltage of the input you are trying to protect. The change to 100R is to limit the current because you a permanently driving it over the 3V3.