3v LCD Source?

[jecottrell]

Hello All,

(Pardon the non CCS topic, but you guys have been such a great help with everything I've run into.)


Tomorrow (Monday) I'll be back on the phone trying to locate the following animal:

3v LCD Character Display, 16x2, 16x4, 20x2, or 20x4.

Design issues are:

3V Radio is required and implies that to keep things simple everything else should be 3V. (I can deal with level shifting and dual supplies if required, but I would like to avoid that.)

Secondary issue is power. My options are 2AA or 4AA. That leaves me with 2.4V (2AA NiCad) up to 7.2V (2AA Li-Ion). I would prefer a 2AA or 4AA Alk-Mang option to eliminate the recharging circuitry (start to get the simplicity drive here?)

So....If I can find a source for the 3V LCD I can use the 4AA Alk-Mang option with a simple 3V LDO and a couple of caps and just live with the inefficiencies of the LDO. (Or more likely a 3V switcher.)

If I can't locate a 3V LCD then things get trickier (I think). My options would be:

1. 2AA Li-Ion, recharging circuitry, 3V LDO and 5V LDO.

2. 2AA (Ni-Cad or Alk-Mang) with 3v Switcher and 5V Switcher, and recharging circuitry if required.

3. Some other topology that hasn't occured to me yet. (I'm not an EE, I don't play one on TV, and I didn't stay at Holiday Day Inn Express last night.)

What I have attempted so far:

Searched the CCS forum for simialr problems. (With no luck.)

Googled 3V LCD. Vishay lists many "5V (3V available)" but trying to find a knowledgeable technical sales rep late on Friday afternoon was impossible.

Brainstormed through all sorts of power configurations, to the point of experiencing a cranial overheat.

Finally, broke down and posted an off topic message in a forum that has provided great ideas in the past.

Thanks,

John


BTW, ran into an EE question while trying to come up with a power solution. Could someone tell me if it is possible to configure a switcher to provide step down regulation when the supply is above the regulated value and step up when it goes below? i.e. 4AA supplying 6V nominal to a 5V switcher. At some point, early in the life of the 4AA Alk-Mang cells the V will drop below the 5V of the switcher and require stepping up.

Or does a switcher inherently provide this functionality?

[newguy]

Many moons ago someone on this board mentioned a very low power consumption LCD that ran on a 3V supply - and it stuck, luckily for you.

http://ca.digikey.com/scripts/DkSearch/dksus.dll?Detail?Ref=450832&Row=178928&Site=CA

It's a COG (chip on glass) 16x2 lcd module. The digikey entry lists its power supply as +3/-7, but I haven't read the datasheet to see what the -7V would be for.

In the original discussion/mention of the thing, someone said that its current consumption was low enough that it could be powered from one of the pic's output pins. I remember that.

[jecottrell]

Thanks for the info. Sorry to add conditions after the fact.....

I would like to use a module (needs to go in an enclosure that is configured for "standard" LCD dimensions. So COG would complicate mounting.

The LCD typically requires Vdd-Vo = 4.5V so that can be statisfied in a 3V system with a simple negative voltage generator. That is typically where the -V number comes into play. (I think.)

John

[jecottrell]

Found a good App Note on the EE question that I posed.

Read about it here:

http://www.maxim-ic.com/appnotes.cfm/appnote_number/661

Hopefully, should be able to find a 3V LCD soon. I have several options I think, but still no sources.

[PCM programmer]

I noticed you posted on the CrystalFontz forum.
Did you see this thread ? Their tech guy says how to do it:
http://www.crystalfontz.com/forum/showthread.php?&threadid=1622&highlight=3.3v

Here are two of their LCDs that have the -V option:
http://www.crystalfontz.com/products/1602b-wt/index.html#CFAH1602BYYHJPV

There are a few more on this page. Any part number that ends
with a "V" has the built-in negative voltage generator.
http://www.crystalfontz.com/products/index-std.html

I haven't tested using an LCD at 3.3v myself.

[jecottrell]

Excellent.

I'm getting closer.

Previously I was concerned about the 3V PIC being able to drive the 5V logic in the LCD controller. But I had gooned up the numbers. PIC should put out Vdd - 0.7V for Voh and LCD controll needs 2.2V for the input. So I should be safe. (I had pulled incorrect numbers from the data sheet earlier.)

I think I may even be able to live without the negative voltage generator LCD module (if one isn't available in the size/config I need) if I use dedicated neg volt generator ( Microchip TC1142) to get the Vdd/Vo bias great enough to have a readable contrast.

Also found a good part for my power dilemma:

http://www.maxim-ic.com/quick_view2.cfm/qv_pk/1742

Just what the doctor ordered.

Thanks!