I'm using a HD44780 controlled LCD, but the display is almost invisible. I'm using a 10k pot from +5 to ground with the wiper to VL to control contrast as the data sheet suggested. If I go from +5 to -5 the contrast is great. Has anyone had similar problems or any suggestions to avoid the dual supply?

 

Wierd, What is VL? I'm not familiar with it from my LCD's... What Pin# is it?

The first three Pins are usually Vss, Vdd, Vee, and I wire it up like this;

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If its for sure a HD44780, then IMO there is someother problem with the LCD than the contrast voltage. Vo +5V thru 0v, using a 10K0 should be OK.

Is the Common 0V line connected from the LCD controller pcb to the PIC 0V line?.

If you must use a -Vo, do you have a MAX232 RS232 ic on the PIC pcb?, if so, you can tap into the -9V on the MAX.

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G'd Day Gramo,

Please check the naming of the LCD power connections in your pix, above.

The Hitachi manual for the HD44780 says:
pin#1 Vss, signal ground.[0V]
pin#2 Vdd, power supply for logic.[+5v]
pin#3 Vo, power supply for LCD driving voltage.[Vo=> +1.5V]

The recommended variable resistor is 10K0 thru 20K0

Regards

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I'm using another type of LCD panels.For the contrast I'm using 5K V/R and sometimes in ohms scale fixed resistor value.

My LCD manufacture recomends that you must connect the V/R in between the V0 - contrast reference supply & Vss - Ground.

If the back light is too bright also its hard to adjust the contrast well.also some back lights like blue colour draws much more current than others.

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Well there you go

My little datasheets said 4.7K to 10K

I'll look around and confirm it

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Spency.

PIC Micro's - Your mind is the limit

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you must have an 'extended temperature' lcd, which requires negative voltage for contrast.

stealing a little -V from a max232 is an awesome and easy idea, you can also generate some using a charge-pump consisting of two capacitors and two diodes driven by a sq. wave from your microcontroller.

another option is a dedicated charge pump controller - Microchip has an easy to use SO8 verison that works with inexpensive ceramic caps.

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Hi,
I use the -V from the max for graphic displays.

You can steal upto 10mA from the +/- lines of the MAX232, I usually make the MAX caps 4.7uF or 10uF, when I do that.
Use the +/- 9v thru 78/79L05 for opa supplies.

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Eric
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