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3.3V Character LCDs

CF Support

Administrator
The controller on our character modules is well within operating range at 3.3v, so that's no problem.

For 3.3v operation of the LCD screen itself, you'll want to pick an LCD with the negative voltage on board, and use the generated voltage from that pin to assist with driving the display, using a 10k pot.
 

jyaron

New member
1) So the LCD design and driving method (Duty/Bias) will
achieve the same contrast at 3.3V?

2) Why do I need an LCD supplied negative bias... I plan on
switched cap inverting the system 3.3V for negative bias.
Is a lower voltage (than -3.3V) req'd for adequate contrast?
 

CF Support

Administrator
A typical character LCD (such as the CFAH1602B-YYH-JPV needs to have a Vlcd of 3.8-5.2v. If you have the LCD driven from a +3.3v supply, then that means pin 3 (Vo) must be set in the range of -0.5 to -2.9v.

If you have one of our "-V" suffix displays, (negative voltage generator on board), then the display makes an output of -3.3v on the Vee pin. You can then use this voltage to drive the potentiometer, which gets connected to Vo.

Of course, if you have a negative supply available, you can use that instead of purchasing an LCD with a negative voltage generator on board.
 

jyaron

New member
I'm probably going with a CFAH0802A-YMC-JP.

Is it correct to assume a VDD of 3.3V is adequate and
it is also OK to use a 10K pot across VDD/VSS with the
wiper to VO for contrast adjustment as depicted in
section 8 of the data sheet?

Or, is a negative bias required and the pot should
be across VDD/-VDD?
 

jyaron

New member
I gottcha, but,

If Vlcd = VDD-Vo and in your specs you say
Vlcd should be 3.9V typical,
why do you offer onboard negative voltage LCDs?

Is the typical Vlcd specified on the data sheet
for the 'barely detectable' contrast?
 

CF Tech

Administrator
The negative voltage generator is offered with the wide temperature range LCDs, which need a higher Vlcd.
 
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