negative voltage lcd

Testing/Troubleshooting
1

I purchased a lcd from crystalfontz.com (http://www.crystalfontz.com/products/2002a/index.html#CFAH2002AYMCJP) and turns out it uses negative voltage…when i connect it to the core i get 2 rows of blocks…ive uploaded the mios sysex and pinged it to make sure it uploaded and was successful. now since it uses negative voltage should i even get anything to display besided blocks?

Thanks

Sean

2

Now it’s being quite a while since I’ve used a display that required negative voltage for LCD. However if I did eye the datasheet correctly it doesn’t need much of negative voltage, only under 1 volt or so, depending on the ambient temperature. So adjusting this on some direction does not have any affect on having black rows or how is it?

Regards, Petri

3

Right now I dont have a way to convert to negative voltage..although I have ordered an inverter…I was thinking of just ordering another lcd with it built in but wouldnt something display anyways or am I wrong? I did adjust the contrast so blocks appeared.. I probably should  go over the soldering again

Sean

4

Can’t say for sure-- but your display CFAH2002AYMCJP doesn’t seem like the one needing a negative contrast voltage…but your probably experiencing some other problems== not that I ever had those,

MOebius

5

turns out it uses negative voltage…when i connect it to the core i get 2 rows of blocks…

as far as i know, you shouldn’t be getting those blocks if you need a negative voltage.  i have a negative voltage lcd and the blocks don’t appear without a negative voltage.

6

Did re-read the datasheet and according to the need of negative VO the datasheet says:

Supply Voltage For LCD = VDD - VO = -0.3…+7V

Which translates to:

VO = VDD - VLCD

And while your VDD is +5V, the VO should be within range of:

5V - (-0.3)V = +5.3V and 5V - 7V =  -2 V

Now these are the maximum values that should never be exceeded or it will break down the display.

However the datasheet also suggests that the typical VLCD would be 4.5V @ 25C temperature, so the typical V0 would be 5V - 4.5V = +0.5V

Did I get it all wrong now? Someone? This is how I interpret the datasheet but something can be lost in the translation :wink:

BTW: A good trick to generate the negative voltage (if needed) is also to use a standard MAX232 or similar RS232 converter. Just feed logical 1 to TX input and voilà, you have generated negative voltage on other side. No need for external inverter, specially if you are working with a design that already have RS232 interface (chips tends to have two RX/TX pairs).

EDIT: One addition. And a typo (again).

7

yea i ordered a 232 not sure what esle is goin on probably wiring or something..lol

Sean

8

BTW: A good trick to generate the negative voltage (if needed) is also to use a standard MAX232 or similar RS232 converter. Just feed logical 1 to TX input and voilà, you have generated negative voltage on other side. No need for external inverter, specially if you are working with a design that already have RS232 interface (chips tends to have two RX/TX pairs).

Hi erverbody!

Couldt anybody explain me how I have to connect my display to the MAX232?

I dont understand how… :frowning: