small colour LCDs

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Can anybody recommend some small colour LCDs that can be easily interfaced
with a microcontroller? If people could tell me how they did it, that would
be even better.

cheers,

C3



Re: small colour LCDs
It appears that colour TFTs are too expensive, so I'll have to settle with a
monochrome LCD like the one at http://earthlcd.com/serial_lcd.htm . What do I
need to look for in a microcontroller in order to drive this LCD?


cheers,

C3



Re: small colour LCDs
On Sat, 7 Feb 2004 22:55:24 +1100, the renowned "C3"

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You can get one with a controller built in. Eg. T6963C, SED1520,
whatever. Then worry about memory size and speed for the size of the
display and whatever it is that you're planning on doing with it, it
only takes a dozen or so lines to interface to the LCD.  

There are microprocessors with graphic LCD controllers on-board, (eg.
Sharp 32-bit ARM LH75400) but I suspect that's more than you want.
There may be microcontrollers too, I've not looked lately.

Best regards,
Spehro Pefhany
--
"it's the network..."                          "The Journey is the reward"
snipped-for-privacy@interlog.com             Info for manufacturers: http://www.trexon.com
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Re: small colour LCDs
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a
I

Sharp has some ARM7 microcontrollers that will do this, such as the LH75410
in your case.  It's about $9 in moderate quantity, down to about $6 in
consumer volumes.  While this seems expensive, it's still competitive
compared to an 8-bit uC + LCD controller IC.  Also, it gives you grayscale
capability with any STN LCD, it has a boatload of peripherals to complete
your product, and it's well supported with cheap development tools.




Re: small colour LCDs
On Sat, 07 Feb 2004 14:06:33 GMT, the renowned "Ian McBride"

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Although Sharp calls these microcontrollers (no doubt due to the
wealth of peripherals that are on-chip, making them almost complete
systems), I'm not sure I agree. They require external program memory.

Best regards,
Spehro Pefhany
--
"it's the network..."                          "The Journey is the reward"
snipped-for-privacy@interlog.com             Info for manufacturers: http://www.trexon.com
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Re: small colour LCDs
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That's only part of the story though. I would not wish a "from-scratch"
project (handful of chips and my blessing) based around one of these
parts on a relative beginner. There are a fearsome number of
interconnects (SDRAM, flash, LCD), potentially some external logic,
quite a bit of bring-up code before you can even be sure it's powering
up right, and basically it's a fairly daunting first-timer challenge.
So, you need to factor the cost of a prefabricated EVB and maybe a JTAG
pod into the equation.

Although the '520 is more expensive per-unit, it's supported by the $199
RMS101 board, and that makes it the "cheapest" overall BlueStreak part
for a project of this nature. I'm not aware of a comparably priced EVB
for Sharp's other parts. Sharp's official development kit is kilobucks
($4500 I think, for the 520's EVB anyway - it's been a while since I
looked at it. They loaned us one for a few weeks to get our bring-up
code validated).


Re: small colour LCDs
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Color TFTs are too expensive? I can happily sell you one out of my
collection of samples that I keep "just because I can't bear to throw
them away". How about a 6.8" LG Philips VGA-resolution (640x480) panel
with parallel input for $60, including backlight inverter and shipping
within CONUS? I have larger panels but they are mostly LVDS inputs (I
could probably find a 10.4" parallel-interface panel in my box-o-joy).

For about the same price, I can supply a 4" color TFT with an NTSC input
board. (It's also possible to drive with an analog RGB and CSYNC signal,
but you have to solder direct to pins of one of the interface ICs, and I
don't have documentation on how to do it).

However, that's the easy part of the equation. How are you going to
drive it? It needs to have data clocked in regularly to keep showing a
picture. You can do it in software using a reasonably fast 32-bit
microcontroller (Tauno, in this NG, has done it on Atmel ARM7s).


Re: small colour LCDs

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Plus a few logic chips, plus the bias generation hw, plus the backlight
controller. Not very expensive, but a lot of things to design
and debug.

Also, the timing requirements of a LCD panel may really be an
uncomfortable feeling in the low lower back. The data must not be
clocked in too fast, and there may be some timing requirements
(line strobes) which really need to be accurate to avoid all sorts
of flickering. Finding the timing specs may be rather difficult
even with a "standard" connnection (DVI is another animal, I am
quite sure it cannot be reasonably done in sw).

In our case, a conventional interrupt was way too slow, and
32-bit FIQ interrupts were used in the middle of 16-bit thumb
code. The code is rather tricky.

The application mentioned above uses a 50 MHz AT91R40008,
and the display controller eats up almost half of its performance.
That is 20-25 MIPS on a 32-bit machine! The panel is only a 320x240
BW panel, one bit per pixel. The situation will be even worse for
more sophisticated panels.

Display controlling is much easier in hw than sw. Unfortunately,
the controller chips are quite difficult to command; even that
route is rather bumpy.

- Ville

--
Ville Voipio, Dr.Tech., M.Sc. (EE)

Re: small colour LCDs
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I don't know about DVI per se either, but the relatively simple LVDS
interface on most panels can be converted from a regular parallel LCD
signal using readily-available encoders ($2.50 last I checked). As
long as you can generate a good parallel signal, the converter will
handle all the gory details of embedding clock and encoding everything
onto the serial lines.

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Yeah, don't I know it :( Sometimes the LCD controller macrocells in
uCs can be surprisingly easy, though. Cirrus 7212/7312 is refreshingly
simple (also unfortunately quite limited, but that's another story).

Re: small colour LCDs
snipped-for-privacy@larwe.com (Lewin A.R.W. Edwards) writes:

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I think the problem is rather on the speed side; the data rate of DVI
is so fast that any micro will have trouble coping with it in sw.
However, I think DVI is better documented than the various parallel
interfaces found on LCD panels. (My experience is mostly from smaller
panels, so the situation may be different in VGA size.)

- Ville

--
Ville Voipio, Dr.Tech., M.Sc. (EE)

Re: small colour LCDs
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The datasheets I've used are fairly accurate, usually. The problem is
more typically in the controller, especially if it's a fancy
controller with 3D graphics, 2D blitter, etc etc built in. I thought I
was a guru from having mastered the OCS chipset on the Amiga (with
multiple resolution changes in every frame!), but really it was
nothing compared to the difficulty of sorting out a simple
fixed-resolution image on a modern SVGA chip.

Worst problem is they don't tell you what MUST be initialized and what
can safely be left at factory defaults. So it can take three weeks
just to get a sync signal out of the chip.

Re: small colour LCDs
snipped-for-privacy@larwe.com (Lewin A.R.W. Edwards) writes:

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Uuuugggghhhhh... I feel sick already...

Our problem was that the far-east display module came with very
little documentation. The 14-pin interface is assumed to be a
standard interface. And it is, in a way. Most LCDs use the same
raw driver signals. However, the timing specs, etc. may differ
from one panel to another. The data may also be fed in from left
to right and up to down or in some other way.

The only way to go was to have a close look at the module and
track the connections. The datasheets of all chips onboard
were available, so all specs could be derived from them and the
PCB.

After that it was only a bit of trial and error; I made a CPLD-
based system which fed a simple bouncing ball picture into the
panel. Fter the image was visible, everything was extremely simple
and easy. (From my point of view, that is. Tauno wrote the
software, not me :)

The funny thing was that even the basic electrical specs shown
on the display module datasheet were slightly odd. First of all,
the signal names had been somehow mixed from those used in the
driver chip datasheet. They had also slightly miscopied the
application example from the driver datasheet. Furthermore,
the panel was spec'd to +5 V, while all the chips were specified
from 3 to 5 V. (Why? I dunno.)

So, nothing awfully difficult, but a lot of stupid little things
that keep you busy for days.

- Ville

--
Ville Voipio, Dr.Tech., M.Sc. (EE)

Re: small colour LCDs

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If it is my personal small project, I would find some here:
http://sales.goldmine-elec.com/prodlist.asp?catid21%35
I am not in anyway related to them.


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