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LCD has all squares until I adjust pot

MrDEB

Well-Known Member
Have a 2 x 16 LCD and a 10k pot to adjust the LCD with but is there a method to avoid having to readjust when changing batteries?
thinking of a voltage regulator? then adjust the pot and hopefully the display will be correct without having to readjust the pot.
 

crutschow

Well-Known Member
Most Helpful Member
thinking of a voltage regulator? then adjust the pot and hopefully the display will be correct without having to readjust the pot.
That should work with an LDO regulator.
What batteries does it use?
 

crutschow

Well-Known Member
Most Helpful Member
Venerable LM317 in a TO92 case
Except that only regulates to with 2-3V below the battery voltage,
So for maximum battery life you want an LDO regulator which typically can regulate to within <1V of the input battery voltage.
 

Nigel Goodwin

Super Moderator
Most Helpful Member
Have a 2 x 16 LCD and a 10k pot to adjust the LCD with but is there a method to avoid having to readjust when changing batteries?
thinking of a voltage regulator? then adjust the pot and hopefully the display will be correct without having to readjust the pot.

What is your circuit?, the PIC and LCD should be running off a 5V regulated rail anyway, and the pot, once set, should never need adjusting.

On one of my commercial projects I redesigned the circuit to use a PWM output from the PIC, passed through a low-pass filter to the contrast pin. This allows me to adjust it from the menu via the buttons, and more importantly it saves me having to set it up after manufacture - the default value is stored in EEPROM (along with all the other settings), so it's already correct when it's assembled, but has the option to adjust it later from the menu.
 

MrDEB

Well-Known Member
I though about this laying in bed this morning and going to measure the voltage on the contrast pin (have 3 similar circuits built) and maybe look at using a zenier diode?
Will investigate later today.
 

danadak

Well-Known Member
Most Helpful Member
I found contrast pins seem to have a narrow optimal V, that varies
one part to another significantly. To get best contrast. So zener maybe
not the best bet. User control as discussed by Nigel excellent approach.


Regards, Dana.
 

Ian Rogers

User Extraordinaire
Forum Supporter
Most Helpful Member
Zener wont help... The LCD contrast is referenced to the + rail on the lcd so if the battery drops in voltage a zener wont work... If you are just running on batteries then Nigels suggestion will be the better option. What processor is it? some have FVR 's ( Fixed voltage registers ) A simple buck boost ie LT1615 will give you a constant voltage even when the batteries drop off.
 

tepalia02

Member
Once I connected a fixed 2K resistor to the V0 pin instead of the variable POT. Don't know if that will work in your case.
 

Nigel Goodwin

Super Moderator
Most Helpful Member
My old 16x2 LCD has instructions for pixel brightness and background brightness
In which case it's not an Hitachi HD44780 compatible one, which uses an input pin voltage for display contrast, and optionally has LED back lighting, who's brightness you can vary by altering the LED current (usually a resistor feeding it).
 

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