LCD 4x20 HD44780

[inteco]

Thanks for your reply.
I'm using PBPro version. When I watch carefully to the LCD, I got
the display output, but it is very blur and almost invisible.
Only viewable from a certain angle. I already adjusted the pot for
the contrast pin from 0-5 Vdc, 0 Vdc still the best, but still
unreadable. Wish there are more space to turn the pot beyond the
pot.
Wonder if there is any type of LCD that need negative voltage
at the contrast pin ?

[inteco]

In fact, I got 2 x 16 LCD, and they all work find with the code,
only the 4 x 20 LCD that has contrast problem.
Thanks

[sougata]

Hi,

Try using a negative supply. If you are using a Centre tapped transformer then you may derive it from there. An onboard Hardware PWM with a diode-cap charge pump can do the same. MAX232 has an onboard charge pump (-12V) available on its VEE pin. So a little experimentation would solve your problem

[inteco]

Thanks guy.
Will experiment with negative voltage later this weekend,
hope I won't burn my LCD : -)

[paul borgmeier]

If you do not want to damage your 4x20 then read the 4x20 datasheet before trying anything else. I have several brands of 4x20s in use and none require a negative voltage on the contrast pin. Yours could be different but read the datasheet first.

Good Luck,

Paul Borgmeier
Salt Lake City, Utah
USA

[inteco]

Thanks for reply.

In fact, I read the datasheet, but somehow it just different from the real world. Anyway, just burn 1 because I plugged in the wrong cable which power up the LCD with 10 volts.

The contrast, indeed need negative voltage of up to -5.7 vdc with relative
to 0/gnd. Whereas the Vdd remain at 5.1 Vdc.

The LCD is made by OPTREX model DMC20481.

[inteco]

Extra Information :
There won't be any need to
DEFINE LCD_LINES 4

PBPro will work too if with DEFINE LCD_LINES 2.

Not really sure if the DEFINE LCD_LINES actually applied.