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'[EE] Reading an LCD'
2007\10\24@221600 by Jinx

face picon face
I need to read a limited number of words that will appear on an
LCD. This LCD will either be a standard 16 x 2 or a custom LCD
with a font that's similar to a standard 16 x 2. There are four words,
of about 8 characters each

I don't need to actually 'read' the words as such, but by the overall
light / dark level of whatever the sensor(s) detects, infer what the
word is. An added complication is that some units are backlit, some
aren't, so I can't rely on transmitted light / blockage contrast

The reason to do it the hard way is that one approachable owner
of a unit requested, amiably and resonably, that his not be tampered
with (yet). This is a proof-of-concept investigation. Once the system
is shown to enhance the product then probably we'll get permission
to open the box and tap into those signals I'd really find easier, and
no doubt much more reliable, to work with

I've tried a couple of experiments with photo-diodes that were a
little bit promising, but not spectacular. Maybe the array from a
scanner would do a better job, although that may involve some
small transport mechanism to move the array across the LCD. But
if that's the best solution, c'est la vie

Just wondering if anyone has suggestions and/or links

TIA

===============================================
If you aren't part of the solution, you're part of the precipitate


2007\10\24@223852 by Richard Prosser

picon face
Optical mouse sensor?

Even a cheap camera out of an old cellphone or toy may not be too
difficult to interface. There was one on hackaday.com not too long ago
IIRC.

RP

On 25/10/2007, Jinx <spam_OUTjoecolquittTakeThisOuTspamclear.net.nz> wrote:
{Quote hidden}

> -

2007\10\24@231429 by Jinx

face picon face
> Optical mouse sensor?

Good thought. I have one with a busted wheel that's otherwise OK.
$7 a go for the whole mouse, would be great if it worked, and I
don't see why it might not

> Even a cheap camera out of an old cellphone or toy may not be
> too difficult to interface. There was one on hackaday.com not
> too long ago IIRC

I picked up some Gameboy cameras a while ago (out they go, $5)
just for hacking. I've got a saved web page about interfacing with
the Mitsubishi "Artificial Retina" chip in the camera

This would be a good excuse to actually do the hacking (might also
give me a chance to look into that camera-in-a-car idea I had)

ISTR past-lister Edson Brusque did some work on image storage,
might look him up


2007\10\25@041542 by Alan B. Pearce

face picon face
>I picked up some Gameboy cameras a while ago (out they go, $5)
>just for hacking. I've got a saved web page about interfacing with
>the Mitsubishi "Artificial Retina" chip in the camera

That would probably be the way to go. My thought was to hack a webcam, but
those would probably be easier to deal with, especially as you already have
them.

2007\10\25@043512 by Dario Greggio

face picon face
Alan B. Pearce wrote:

> That would probably be the way to go. My thought was to hack a webcam, but
> those would probably be easier to deal with, especially as you already have
> them.

Sparkfun has some cameras with RS232 or SPI interface.

--
Ciao, Dario

2007\10\25@052941 by Jinx

face picon face
> Sparkfun has some cameras with RS232 or SPI interface.

Thanks. The prototype will be a hack (haven't had a good old
hack in a while), something OTS will be useful for the future

My only concern might be whether the focal length is short
enough to capture the LCD characters cleanly, have to look
into that

2007\10\25@061743 by Richard Prosser

picon face
You can focus in closer by moving the lens further out (external lens
mount, extension tube etc.) or by just adding a magnifying glass
between the camera & the LCD.

RP

On 25/10/2007, Jinx <.....joecolquittKILLspamspam@spam@clear.net.nz> wrote:
> > Sparkfun has some cameras with RS232 or SPI interface.
>
> Thanks. The prototype will be a hack (haven't had a good old
> hack in a while), something OTS will be useful for the future
>
> My only concern might be whether the focal length is short
> enough to capture the LCD characters cleanly, have to look
> into that
>
> -

2007\10\25@171638 by Jinx

face picon face
> Gameboy cameras

Looking into the old data I have, found this

http://www.merl.com/

Some interesting projects and topics

Quite glad I did save Gameboy web pages, many links are
now dead

2007\10\25@225111 by Robert Rolf

picon face
Jinx wrote:
> I need to read a limited number of words that will appear on an
> LCD. This LCD will either be a standard 16 x 2 or a custom LCD
> with a font that's similar to a standard 16 x 2. There are four words,
> of about 8 characters each

Do the four words have significantly different numbers of active pixels?
If so, you could just using a pair of photon detectors to measure the
area covered by pixels. One sensor for the text, one over an 'always blank'
area to compensate for backlight variance (or your supplied front light) differences.
I would suggest that if the words are variable length, to mask the
text sensor to use the fewest characters to maximize the differences detected.

> I've tried a couple of experiments with photo-diodes that were a
> little bit promising, but not spectacular. Maybe the array from a
> scanner would do a better job, although that may involve some
> small transport mechanism to move the array across the LCD. But
> if that's the best solution, c'est la vie

You can also get photodiode linear arrays. Just image a line of the display
with a relay lens and you should be able to come up with enough different
values to be able to distinguish the texts. They don't need to be sharply
focused, nor perfectly aligned if you have a 'calibrate' routine to learn
the values for each text.

I see this a being easier to interface than using a full blown camera.

Robert

2007\10\25@231724 by William Jacobs

flavicon
face
Jinx,
It may be easier to use a TV camera.  It you were to make the lcd image
large on a TV set, you could look at certain TV line at a certain time
and know that only word x has a high at that spot.
You would need a sync separator to count the lines of the frame and then
a timer, say timer 0 to delay so many micro seconds after the sync pulse
then read the output of the  camera. with an a/d.  You could find
several places on the frame to re-confirm the data.
It would still cost several dollars for the camera and electronics but
the interface should be easy and you do not have to touch the original
product.
Just my thoughts
bill
hopefully,  part of the solution,


Jinx wrote:
{Quote hidden}

2007\10\26@042528 by Dario Greggio

face picon face
Robert Rolf wrote:

> You can also get photodiode linear arrays. Just image a line of the display
> with a relay lens and you should be able to come up with enough different
> values to be able to distinguish the texts. They don't need to be sharply
> focused, nor perfectly aligned if you have a 'calibrate' routine to learn
> the values for each text.
>
> I see this a being easier to interface than using a full blown camera.

Yep, I did think of this too: the kind of those used in scanners.

--
Ciao, Dario

2007\10\26@100938 by William Couture

face picon face
On 10/25/07, Jinx <joecolquittspamKILLspamclear.net.nz> wrote:
> > Gameboy cameras
>
> Looking into the old data I have, found this
>
> http://www.merl.com/
>
> Some interesting projects and topics

I know someone who works there.  Should I tell Crash that
you've stumbled on his work?

(http://www.merl.com/projects/iGlassware/ among others)

BTW:  If you watch "Scrapheap Challenge" ("Junkyard
Wars" for the Americans), he's the same Crash...

Bill

--
Psst...  Hey, you... Buddy...  Want a kitten?  straycatblues.petfinder.org

2007\10\26@102107 by Peter P.

picon face
I think that it depends how desperate you are. I think that using a row of about
4 to 8 photodetectors as the 'sensitive element' in a 'camera' that uses a
single lens to image the display out of focus onto the detector row might work
well, after training. For the reflective type you will have to supply a light
source
and the problem reduces to the initial one I think. Of course I assume this
occurs in a black box with no stray light from the outside. Perhaps something
temporary made of cardboard painted flat black and attached on the outside with
tape to the existing display. The detectors would have to be read by A/D and a
table made and from that discriminator levels deduced. Each unit will likely
need training and temperature compensation (the lcd transmission changes a lot
with temperature). For ideas on the shape of the box take a look at scope camera
attachment jigs. There are a few good pictures of that on the web. I have used
such a box to project the text from a b/l lcd onto a wall. Mirrored of course.
The mirroring can be removed by using the box upside down and one (!) flat
mirror to bend the output 90 degrees. The image is visible in a dark room. The
type of LCD where the background is dark and the segments are light works better
for this.

Peter P.


2007\10\26@181555 by Jinx

face picon face
> For the reflective type you will have to supply a light source

I think that's going to be the tricky one. You can't get right up
against the LCD glass of course, there's a layer of protective
plastic as well, and each reflection and refraction is going to
possibly smudge the light available for the diode, at close range
anyway

However, that said, I could be completely over-estimating the
problem. With the right source and diode(s) it might be a snip

A couple of the words are very similar, both in actual matching of
letters and pixel count of letters that aren't the same. The only
significant difference is at a letter position where one has a P and
the other has an I. E vs L might be detectable too

> I assume this occurs in a black box with no stray light from the
> outside

That was the intention. It may come about that, even if our process
is accepted, it is still not permitted to open the units (warranties,
security etc), and I'll have to worst-case design this to always work
from the outside looking in. So what works in the prototype may in
fact become the final method

2007\10\26@181555 by Jinx

face picon face
Bill,

> It may be easier to use a TV camera

The adventurer in me would love to try a camera, but the worn-out
time-short sick-of-clocks-and-data in me wants to try diodes first ;-)

> You would need a sync separator to count the lines of the frame

I hear what you're saying, but a Gameboy camera, which is what I
would try if and when I have to, has no frames. It's a long sequence
of pixels that the user has to break down back into the 128 x 128
image

> Just my thoughts
> bill
> hopefully,  part of the solution,

Appreciate the input

Thanks also to everyone's feedback



2007\10\27@060511 by Jinx

face picon face
> photodiode linear arrays. Just image a line of the display and you
> should be able to come up with enough different values to be able
> to distinguish the texts

> I see this a being easier to interface than using a full blown camera

I've tried some different diode circuits and a backlit display, and
whilst you can vaguely tell light from dark areas, the resolution is
very poor. Mostly the problem is that you just can't get in close
enough to the pixels. A circuit that works well with black lines on
paper has a feeble output with an LCD

One real bummer is that a diode detector will have to be positioned
to the pixel for it to work reliably. And, as I mentioned, there are
many styles of this display that the information is shown on. 16 x 2
is one thing, but dealing with graphic or custom screens is another

So at the moment, AFAICT, diodes are too coarse. It looks like
the Gameboy Camera may get an outing after all

I'll have to check the principal's commitment to the project before
starting anything that time-consuming though

2007\10\27@191027 by Jinx

face picon face

> I know someone who works there.  Should I tell Crash that
> you've stumbled on his work?

OK

> BTW:  If you watch "Scrapheap Challenge" ("Junkyard
> Wars" for the Americans), he's the same Crash...

Haven't seen that for ages, and only a couple of episodes ever so
don't know Crash. It's on a pay channel I don't have, but once in
an unannounced while it's unscrambled

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