LCD negative VEE requirements

[alhoop]

I have a 2 line X 40 character LCD display that requires a negative 1 volt for vee(contrast). I understand that this is standard for extended temperature range units. Does anyone have a simpler circuit for generating a negative 1 vdc from + 5vdc than this:
(from David Covick web site)

Thanks
Al

 

[Dippy]

Looks nice and simple to me.
Perhaps someone can think of something with one less component.

If you wish to 'save' your PWM facility for something else, then consider an inverting chip such as the 7660. No doubt there are others....
Please check Data Sheet for proper component descriptions etc.

 

[Andrew Cowan]

I'll second the MAX7660 charge pump. I have used it for GLCD discplays, and found it to work very well. Easy to use, too.

A

 

[MFB]

Is the ratio of the two capacitors on the charge pump schematic correct? I think the input capacitor should be smaller than the output capacitor, not larger.

 

[MartinM57]

...or if you happen to have a MAX232 in your circuit (unlikely, probably ) then you could use the (probably) unused second channel to generate the -ve voltage by just applying +5V to it's input...

 

[Dippy]

MFB.
Maybe it depends on Manuf. ?

Other than that I don't know what to say, other than 'it works'.
And.... page 6 Figure 11.
http://www.farnell.com/datasheets/31973.pdf

I try not to think

If you are referring to C3, thats just a fat deoupler.
The Data Sheet layout may be easier to follow.

 

[ArnieW]

I'll second the MAX7660 charge pump. I have used it for GLCD discplays, and found it to work very well. Easy to use, too.

A

I'll cast another vote for the 7660 - I used mine on a 2x40 LCD.

 

[BeanieBots]

I'd stick with the first diagram published.
It really is quite basic and does work. (I'd make C7 ten times bigger though).
Then you will be able to control contrast under software control which the 7660 solution would not permit.