soudan Posted April 8, 2005 Report Share Posted April 8, 2005 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?ThanksSean Quote Link to comment Share on other sites More sharing options...
MMorph Posted April 8, 2005 Report Share Posted April 8, 2005 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 Quote Link to comment Share on other sites More sharing options...
soudan Posted April 8, 2005 Author Report Share Posted April 8, 2005 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 againSean Quote Link to comment Share on other sites More sharing options...
moebius Posted April 9, 2005 Report Share Posted April 9, 2005 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 Quote Link to comment Share on other sites More sharing options...
jdutcher Posted April 9, 2005 Report Share Posted April 9, 2005 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. Quote Link to comment Share on other sites More sharing options...
MMorph Posted April 9, 2005 Report Share Posted April 9, 2005 Did re-read the datasheet and according to the need of negative VO the datasheet says:Supply Voltage For LCD = VDD - VO = -0.3...+7VWhich translates to:VO = VDD - VLCDAnd while your VDD is +5V, the VO should be within range of:5V - (-0.3)V = +5.3V and 5V - 7V = -2 VNow 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 = +0.5VDid I get it all wrong now? Someone? This is how I interpret the datasheet but something can be lost in the translation ;-)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). Quote Link to comment Share on other sites More sharing options...
soudan Posted April 9, 2005 Author Report Share Posted April 9, 2005 yea i ordered a 232 not sure what esle is goin on probably wiring or something..lolSean Quote Link to comment Share on other sites More sharing options...
Marxon Posted January 28, 2006 Report Share Posted January 28, 2006 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... :( Quote Link to comment Share on other sites More sharing options...
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