### Author Topic: NHD-0212WH-ATMI-JT# on 3.3V  (Read 4233 times)

#### DaveG

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##### NHD-0212WH-ATMI-JT# on 3.3V
« on: February 17, 2015, 01:16:29 PM »
Is it possible to run the NHD-0212WH-ATMI-JT# with Vdd = 3.3V if V0 is connected to a negative supply?  I know this can be done with other displays that use the ST7066, but it's not mentioned the datasheet for this display.

#### Paul_B

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##### Re: NHD-0212WH-ATMI-JT# on 3.3V
« Reply #1 on: February 17, 2015, 05:05:34 PM »
Hello,

To answer your question no, the optimal contrast needs to be around 0.8V. Please see page 5 in the displays data sheet for the electrical characteristics.

http://www.newhavendisplay.com/specs/NHD-0212WH-ATMI-JT.pdf

#### DaveG

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##### Re: NHD-0212WH-ATMI-JT# on 3.3V
« Reply #2 on: February 17, 2015, 05:43:09 PM »
Hi Paul,

Not sure I made my question clear.  In the datasheet, page 5, "Supply for LCD(contrast)" is spec'd as "VDD-V0", 4.2 volts.  Yes, for a +5 VDD, optimal V0 would be +5 - 4.2 = .8 volts.  But, if VDD = +3.3 volts, V0 would be +3.3 - 4.2 = -1.1 volts.  The datasheet for the ST7066 says it will work with VDD = 3.3 volts and V0 negative.  Is there any reason this LCD won't work that way?

#### DaveG

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##### Re: NHD-0212WH-ATMI-JT# on 3.3V
« Reply #3 on: June 10, 2015, 12:02:05 PM »
Well, I tried it anyway, and it does work.  You can run this display on 3.3V.  V0 gives good contrast in the -0.6 to -1.2 volt range.  I generated the negative voltage with a simple charge pump circuit driven by the PWM output of the microcontroller.  Changing the PWM duty cycle allows for software adjustment of the contrast.