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Topic: LCD 16x2 is not display anything (Read 2374 times) previous topic - next topic

floresta

Now that the hijack is over I wonder how the original poster is doing?

Don

xianwu

I wonder why Vo has to be low to make it work.
in my case Vo = 0.45, if Vo is high(3.3V) then nothing show up.
what's the relationship between Vo(pin3) and LCD contrast?

Xianwu

floresta

It is measured with respect to the logic supply voltage (pin 2) and it is typically around -4.5 volts.

Don

Paul__B


I wonder why Vo has to be low to make it work.
in my case Vo = 0.45, if Vo is high(3.3V) then nothing show up.
what's the relationship between Vo(pin3) and LCD contrast?

You certainly will not get anything showing up with Vo at 3.3V.


It is measured with respect to the logic supply voltage (pin 2) and it is typically around -4.5 volts.


That is the trick.  And it is quite sensitive also, so if your supply voltage drops significantly below 5V, say just to 4.75V as on the (apparently!) heavily loaded USB port next to me, this has the same effect as changing Vo from 0.45V to 0.7V and whilst the LED is almost as bright as ever, the contrast is fading badly.

Now there are some LCD displays available which operate from a 3.3V supply.  This is interesting - they do this by incorporating a "charge pump" IC on the display module - you will notice the SOP "footprint" for this option labelled "U3" on the back of your LCD module and a soldered jumper "J1" which bypasses the charge pump (so if you have a 3.3V module, you could switch it to 5V and back if you wanted to).  This charge pump boosts the internal supply voltage to 5V while the HD44780 happily accepts the 3.3V logic inputs.  You still adjust the Vo to about 0.45V as before, though with the potentiometer now connected across 3.3V rather then 5, its position will be somewhat different.

MAS3

TM_Soundhararajan:
Sure.

Welcome to this forum.
First guide to forums like this is to not hijack (ongoing) threads.
If you have an unrelated question, start your own thread.
Now you are distracting from the OP's question with a totally new question which isn't nice and isn't needed in any way.

Then your problem.
Did you initialize the display correct, telling that you have 16 characters and 2 lines ?

Read the "How to use this forum", found on top in every subforum over here.
Then start a new thread, remove above post (i will remove this one after that) and post it in a new thread.
Or ask a moderator to move the question to a new thread.
Put your code (all of it) in that thread and use code tags.

Have a look at "blink without delay".
Did you connect the grounds ?
Je kunt hier ook in het Nederlands terecht: http://arduino.cc/forum/index.php/board,77.0.html

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