Low Contrast on LCD - help

[Guest fullington99]

Greetings,I've almost got my LCD's hooked up thru FSLCD and the parallel port. I say almost because I'm getting very low contrast (almost invisible), but what I can see shows a correct display based on my FSLCD setup. No spec sheet came with it, but I was able to locate the manufacturer and found spec sheet on other specific models in the series, but not my particular one = Tianma TM402CD P-5, 40x2 with LED edge lighting. (Tianma - http://www.tianma.com/comparative_table/tm402c.html). The LED backlight is lighting up nicely.I have no trimmer pots or resistors installed (tried them on both contrast and backlight but found they didn't do much good for either. So my pin 3 is going straight to ground.I'm a bit new at all this so any suggestions are appreciated. I checked the voltage between pins 2 and 3 and get 4.95. Best RegardsMike.

[iwik 0]

Hi Mike,Suggest you connect your pot between pin 3 and ground(wiper to pin 3, one of other connections to ground).Just had a look at the Specs for one of those lcds and it says that pin3 (VO)is LCD negative.The original connects that pin to plus.Hope this helpsLes

[Guest fullington99]

Les, Thanks for your reply! That's helped but still the display is not completely right. With the trimmer pot (10k) turned full clockwise I now get the first few characters, but still not with full contrast. Do I need a resistor here somewhere? A higher pot? Or am I going to need to wire to a -3.3 v instead of ground? Best regards, Mike.

[iwik 0]

Hi Mike,It looks like pin 3 should be about 0.3v for normal operation.As this pin is the negative supply for LCD,this is all you really have to play with.Try increasing the pot value,measure pin 3 and see if you have about 0.3 and maybe try to get this value.Now that you have some displaysee which way the pot is going to give you more contrast.This will give you a clue.most lcd type will give a full row of charaters with full contrast controll and no drive.Hope this helps.The chip set is not familiar and the FSLCD was designed to run with the Hitachi chips.Could be some diff here.Les

[npbosch 0]

Hi MikeDid you get it right?I also see only the first 8 characters lighting up (1 x 16 display). What do I need to change?When the first 8 characters are lit brightly , I measure 1,5 mvolt on pin 3 (displayvoltage), when I turn the 10K pot ccw the 8 characters disappear and I measure 5.14V (both times compared to ground).When I measure the resistance between pin 3 and ground it is 0 ohm when the 8 characters are lit.Any help would be very much appreciated.ThanksNorberthttp://home.wandoo.nl/norbert.bosch/

[tigert 0]

If it's 1x16 and you only see 8 chars, it could be that the display is internally a 2x8 one, so try that mode too, if it helps.Those things exist.Also, did you notice IOCards now has a USB LCD card that can drive 4 of such displays? :) Nifty!//Tuomas

[Guest washburn_it]

Norbert:if your display is a HD44780 compatible then probably there is a mistake during the initialization of the display.If you go to my website http://digilander.libero.it/washburn_it I explane how to drive a 8x2 LCD display through the parallel port and how to initialize it (initialization on page 2 of the LCD section).Of course you must specify "1" to the number of lines if you have a 16x1 display.The number of characters for a single line doesn't need to be specified.Hope this helps, regards.Bob

[tigert 0]

You know about FSLCD, right?http://mikkila.wabbits.org/fsbus/lcd///T

[npbosch 0]

Bob & ThomasThanks for the help.I use FSLCD to drive my LCD and it is hd47780 compatible. I use the EA W161 B-ENLWDatasheeth:http://home.wanadoo.nl/norbert.bosch/lcd.pdfI just tested it together with FS. I have it built into my trim panel to get a visual feedback of the trimsettings.Because I only have 8 characters (for the moment) I used aileron and rudder trim and it works great. Would love to have the elevator added too.I can adjust the contrast and the backlight as it should. (but why the #$%^&^%$ do the last 8 characters not lit?)I studied the link of Bob. AFAIK I use it in 8 bit mode (d0-d7 connected to lpt). I use the scheme from the fslcd site.Bobs link gives detailed programming instruction about initializing the lcd. I think fslcd does that for me.Thanks Norberthttp://forums.avsim.net/user_files/158816.jpg

[Guest washburn_it]

Connecting the R/W pin to GND (then you can't read data from LCD, not always necessary) would free a pin of the parallel port that you could use to drive the "E" pin of a third LCD so that you can drive 3 LCDs with only one parallel port.In this case you should modify the program (or build a new one) to drive them.Just a suggestion as possible further upgrade.Regards,Bob

[tigert 0]

Looks like I need to add a link here to make people notice :-)IOCards USBLCD Manual (spanish): http://www.opencockpits.com/modules.php?na...p=getit&lid=2731T16 Mounting kit for USBLcd card(PCB+components+Micr.writed+USB cable)(4 lcd cable not included)21 Eur AVAILABLE 2T16 USB Lcd card completely finished and tested (including USB cableand cable for 4 lcd)30 Eur AVAILABLEJust noticed it yesterday. Lets you hook up FOUR into one card, and since it's USB... :)//T

[Guest washburn_it]

Very interesting object.I'm working around something similar but I want to drive up to 20 LCD HD44780 display through just one USB board.Unfortunately implementing USB peripherals is not so easy as I thought and it's taking a long time to me but USB it's very flexible and I think it's worth.Regards,Bob

[npbosch 0]

I promised a pic of my trim panel. Here you see engine 1 inop. Aileron and rudder is trimmed to the right.Unfortunately I still was not able to bring the last 8 characters to life. I had planned this situation" E 2,6 A 0,0 R 0,0". In that case I would also have a visible feedback of the elevator trim position.How do you guys get feedback of the elevator trim?regardsNorberthttp://home.wanadoo.nl/norbert.bosch/http://forums.avsim.net/user_files/158993.jpg

[Guest washburn_it]

Nice panel...it sounds strange that you can't write the other 8 characters.Have you tried with another display?Reading the datasheet, native number of characters displayed are 8, then the other 8 are written using a so called "extension driver" (that is internally managed by the HD44780) that writes from the column 08 till 0F (hexadecimal).Regards,Bob

[npbosch 0]

Yes I tried with a second display that I bought from another shop than the first. Same result. Unfortunately both displays are from the same manufacturer. The first one , is blown up because I was experimenting with all kind of resistors and voltages. But that one did also only show the first 8 characters.regardsNorbert