SparkFun Forums

[hneve]

Hello.

I just wonder if i can use a higer value potmeter than 10K on the contrast ?

i have broken the one i have , and have only 100K and 1k left , but dont want to use 1k

[Ross Robotics]

I don't see why not. You will have to turn it a lot slower and it will get really dim before you reach the stop on the pot..

[Renate]

I've always found that the contrast pots have lousy range when wired to ground and 5V.
I find that wiring them 2 terminal style from the contrast pin to ground works out better.
Yes, you need a 10K because there are 5 resistors that are on the PCB with the Hitachi chips.
The value of your pot is determined by that.

[Ross Robotics]

Yes, you need a 10K because there are 5 resistors that are on the PCB with the Hitachi chips.Yes, you need a 10K because there are 5 resistors that are on the PCB with the Hitachi chips.

What makes you say that? There is only one resistor (variable) for the contrast. You don't even need a pot. You can use a couple of resistors in replacement of the pot..

[Renate]

You could use a fixed resistor, but those LCDs are very sensitive to temperature, supply voltage and viewing angle.
That's why many devices have either a front panel pot or software control of the contrast.

Check out the Hitachi HD44780U spec sheet.
The driving waveforms for the LCD come from a ladder of resistors using up to 6 different voltage levels.
Hitachi does not specify anywhere what value to use for the 5 resistors.
The value is chosen by the LCD makers who use the Hitachi controller.

I measured a board once and it was 2.2K for each resistor.
The board came with an external 10K trimmer thrown in.
By adjusting this between the extremes of conceivably useful values I came up with a range.
A 2.5K trimmer would work better covering the range.

Note: This is all using the trimmer as a variable resistance to ground (no Vcc connection).