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How is a general 16x2 LCD display contrast defined? Is it with voltage on pin V0 or with total resistance of potentiometer?

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  • \$\begingroup\$ Kindly Provide the data sheet link so it will be helpful to go through this \$\endgroup\$
    – Photon001
    Commented Jan 18, 2016 at 10:22
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    \$\begingroup\$ It doesn't appear to have a V0 pin? \$\endgroup\$
    – Andy aka
    Commented Jan 18, 2016 at 10:27
  • \$\begingroup\$ Datasheet: sparkfun.com/datasheets/LCD/HD44780.pdf \$\endgroup\$
    – legend
    Commented Jan 18, 2016 at 10:37
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    \$\begingroup\$ I'll say it again then: It doesn't appear to have a V0 pin!!! \$\endgroup\$
    – Andy aka
    Commented Jan 18, 2016 at 10:39
  • \$\begingroup\$ en.wikipedia.org/wiki/Hitachi_HD44780_LCD_controller No Vo pin? \$\endgroup\$
    – legend
    Commented Jan 18, 2016 at 10:41

2 Answers 2

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In LCD display,the contrast is about the voltage,you supply for the V0 pin.Assume that the maximum voltage that the V0 tolerate is 5V.And also assume that you have a variable resistance.

    Now at lower resistance,the voltage drop across the resistance is small,so large amount of contrast is obtained.
    For high resistance in the variable resistance,the voltage drop at the variable resistance is large,hence the voltage at V0 is appears to be low.So you get less contrast.
    It's all about ohm's law with the variable resistance
    The voltage at the V0 pin affect the contrast.The voltage is now affected by the variable resistance
    Resistance is directly proportional to voltage and voltage is directly proportional to the contrast

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The contrast is controlled by the gap between VCC and V0. On most of the displays I have, in practice, the correct value for V0 is basically ground. The claim above that voltage is directly proportional to contrast appears to be precisely backwards.

The 44780 itself doesn't have a V0 pin; it has V1 through V5 pins. However, the commonly used boards with HD44780s in them that places like Sparkfun and Adafruit ship, which have part numbers like HM2004E, or LCM2004E, have a V0 pin. And, at least on mine, they also have a 5-resistor ladder of 2.2k resistors labeled R1 through R5. Some models also have some contacts for adding some fancy hardware to let you get V0 down to -2V or so for use when driving the whole display at 3.3V otherwise, because the LCD still needs about a 5V range to get reasonable contrast.

So far as I can tell, the potentiometer's resistance doesn't matter; I get the same results with 10k or 100k, but in both cases, I only get usable contrast when I've got the voltage down as far as I can get it or close to it, so effectively 0V from ground.

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  • \$\begingroup\$ "The claim above" doesn't make sense on SE sites as answers are sorted by votes or user sorting preferences. Reference the post by username instead. Welcome to EE.SE. \$\endgroup\$
    – Transistor
    Commented Jun 7, 2021 at 7:46
  • \$\begingroup\$ oh, good point. the claim in question was the claim that the maximum voltage of V0 is 5V, and that higher voltage at V0 gives more contrast. The contrast comes from the gap between VCC and V0. \$\endgroup\$
    – Seebs
    Commented Jun 20, 2021 at 5:17

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