LCD 4x20 HD44780

Lee Sadeli

Hi,

I got a 4x20 LCD with the attached specs, and connected and·tried it with BS2
but it doesn't work. Anyone knows if this LCD is compatible with BS2.

Thanks
Lee

Jon Williams

It looks like it should be -- double-check your connections (don't forget the contrast pot) and the code you're using. StampWorks has LCD experiments that will walk you through everything and may help you sort out the problem with this LCD.

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Jon Williams
Applications Engineer, Parallax

Lee Sadeli

Hi Jon,

All connection are good, now I get a very blur display, which can only be read from a certain angle.
Even though I already grounded the contrast pin (pin #3). Wonder should I need a negative
voltage for this LCD? Attached on my previous message is the specs docs.
If yes, how can I generate one ?

Thanks in advance

Jon Williams

Do not ground the contrast pin -- the spec clearly shows you need to connect the wiper of a 10k pot to it (the wiper will supply a constrast voltage of 0 - 5 volts). See figure 4.2 in that document.

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Jon Williams
Applications Engineer, Parallax

Lee Sadeli

Tried 0 - 5 Vdc with 10K pot, adjusted it.
0 get the best, but still unreadable. Unlike my other 2x16 LCD.
Wonder if there is other type of LCD than regular that may need negative voltage
at Contrast pin ?

PJAllen

"Extended-temperature" LCDs may require a Negative voltage.· If so, it's not a lot, rig up a couple of 'AA' batteries in series (-1.5V may suffice.)

Lee Sadeli

Thanks guy. I'm going to use a desktop PC power supply to do the research. It has all kind of voltages:+/- 3.3,5,12,0, etc. Hope I won't burn the LCD.

Lee Sadeli

Got It !!!
Yes, indeed the contrast pin need negative voltage of
-5.7 Vdc with relative to 0/GND.
Now they are dark and clear.

LCD made by OPTREX model # DMC20481.