On Tue, 1 Nov 2005, James Seely wrote:

> >  Thanks to all for the suggestions. Here are some of them with responses.
> > Sorry this is kind of long but I wanted to get it all together. I also seem
> > to have had some success I discuss towards the bottom.
> >
>   "You need to initialize your LCD to display any thing as far
> contrast you should see the change on the screen.
> Check the voltage on contrast pin ? what 's the voltage ?"
> <james>I'm trying to initialize the LCD with the Predko code but I'm not
> certain that code is correct. I have a 10k pot hooked up to the contrast pin
> and I can take it from 0v to 5v and never saw a difference in contrast.
>  "Maybe the screen IS initialised but there's no data displayed ?"
> <james>A definite possibility but I should at least be able to see the
> contrast adjust with no data being displayed (if I have a function LCD and
> have wired it correctly)
>
> "LCDs are pretty unforgiving about over-voltage on Vcc and it doesn't
> take much to stuff them. It's never accidentally had (much) more than
> 5V on it ?"
> <james> It is entirely possible. I have a couple of kids that are interested
> in my project that might have helped me out (why have kids if you can't
> blame them for stuff...). If I'm reading the spec sheet right it looks like
> 7v is the max it can handle and I highly doubt I've been over that. I say
> that because I built a little 5v power supply from a schematic and it
> actually only puts out something like 4.4v. I then hooked this up to one of
> those fancy power supplies that lets you set the voltage and current and I
> may have been over 5v when I ran up the voltage but only by a quarter volt
> or so.
>  "However, extended temperature
> LCDs require negative voltage on the contrast pin. Some of them will show
> absolutely nothing until the contrast pin gets below zero"
> <james> I don't think I need a negative voltage but how exactly woul I do
> that if I wanted to?
>   Some success?
> I've been playing with this a bit tonight and seem to have stumbled across
> something that made this sort of work. I was testing the voltages between
> the Vdd pin and the Vo pin to see what they were after messing with the pot
> and at one point I shorted between them. My board rebooted and suddenly I
> saw some dark squares! Not exactly time for the happy dance but I may be
> making progress with this. Now when I adjust the pot I do see the contrast
> go up and down. I don't seem to see the pixels show up until that pin is
> about 1.2v. Not sure if that's good or bad. Still don't see the text I'm
> trying to ouput though.
>  Thanks to everyone for the suggestions. If anyone else happens to have seen
> these types of issues I'd still like to hear final resolutions as this seems
> a little too magical. I've written software for a while now and have always
> seen magic code (that debug version that doesn't have the problem that the
> release version does) but I didn't know the electrical side of things had
> the same sort of magic. I understand the software magic. Just wish I
> understood the electrical magic a little better.
>  Thanks,
> James
> --

I don't know about the Predko code, but this is the first
code I got working on an LCD.

http://www.piclist.com/techref/piclist/cheapic/worktime.htm
It's for a F84 but should port to something else easily
enough.

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