LCD Contrast on CFAG14432B

[cbarberis]

Hi,
I noticed that on the data sheet for this display there seems to be no depiction of an outboard contrast adjustment. Although after I initialize the device, the default contrast is not too bad, you can still see the outline of the pixel field, any way to externally adjust this, please advise.

Thank you

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[cosmicvoid]

What have you connected to pin 3 (Vo)? I suspect you have it grounded, and that gives slightly too much contrast. The usual arrangement is a 10K pot from +5v to ground, with the wiper connected to pin 3. Then you can adjust the contrast, although the setting will be close to the ground end of the pot.

Under wide temperature conditions, you might need to take Vo below ground, which would require a negative supply.

 

[cbarberis]

I left pin 3 open, looked to me like that was a voltage output of some sort. Is this part of the contrast adjust?

 

[cosmicvoid]

Yes it is. It is peculiar that the data sheet shows pin 3 as an output, because virtually all other passive displays show it as an input. Another strangeness is that the LCD bias voltage, Vo, is referenced to ground, whereas in virtually all others it is referenced to Vdd (+5v).

In fact, as I look at the data sheets for the other 14432s, the A, C, D, and E series, they all show pin 3 as "supply voltage for LCD", and some sheets show the pot hookup. It looks like the extended temperature situation requires a positive voltage above 5 v, not a negative voltage like most other displays. Some of those models have the higher voltage output generated on-board (Vee).

So you should still hook up the pot, but I'm thinking the useful settings will be close to the +5 end, instead of the ground end.