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is it possible to use resistor instead of POT in GLCD connection

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ep.hobbyiest

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Hi,
I was refering following circuit diagram for glcd 128x64 lcd.
[Scroll 30% of the way down page. Weblink updated by moderator.]

https://embedded-lab.com/blog/lab-20-interfacing-a-ks0108-based-graphics-lcd-part-1/

[plain schematic found at embedded-lab .com /blog /wp-content /uploads /2011 /12 /GLCD_Ckt .jpg]

i have doubt, Can we use resistor instead of POT which is connected for contrast?
because we will setting some value only using POT. So, instead of using POT, i was thinking.
If yes, What value is preferred?
 
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There is no preferred value, but a narrow range near to zero, because the contrast effect on each LCD module may vary from one device to another.
 

Usually, I'm using devider made by two resistors, but I'm not define value at prototype stage. Later on looking for better value and using it for futher solutions.
 

Hi,

The best is to consult the GLCD datasheet (like so often)
There you will find about useful V_contrast range, and usually it's temperature dependence.
Maybe you even find a circuit for generating a temperature compensated contrast voltage.

Klaus
 

Although it is pretty clear what you want, the motivation behind it remains mysterious, therefore without knowing the context, there is a chance to not giving you the tip you really need ( e.g: no space to fit the POT on the board/equipment? adjustment must be done just once during production stage? etc.. ). Anyway, as an ( laborious ) alternative to that, you could think on making a voltage divider with a resistor-array being each one in series with the next, but with a solder jump in parallel with all them so that you could trim the suited value just cutting ( actually melting ) the solder jumper. The drawbacks on this approach are: 1) You should hit the optimal contrast at the first try, otherwise should drop another solder there. 2) This should be done with the equipment de-energized ( the solderingiron could have some leakage current from mains).
 

DAC is good idea instead of POT. But PWM also can do the same thing if DAC is not free. But i think we ll need to add filter for PWM, right?
 

Hi,

Yes, I recommend RCRC.
For second order..to reduce ripple to a minimum.

Klaus
 
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