Barcode scanning on LCD display

[MS Ian]

Hi all,

Stupid question...can a normal barcode scanner scan from an LCD
display displaying a barcode (instead of from scanning from paper and
ink)?


Cheers,
Ian

 

[John Fields]

On 6 Jul 2004 06:42:22 -0700, msian@canada.com (MS Ian) wrote:

Hi all,

Stupid question...can a normal barcode scanner scan from an LCD
display displaying a barcode (instead of from scanning from paper and
ink)?

---
If the barcode is being displayed statically, then I think there's a
pretty good chance you could scan it and get back the data you're
looking for. If its being multiplexed, then I think you'll get
garbage back.


--
John Fields

 

[Kevin R]

On 6 Jul 2004 06:42:22 -0700, msian@canada.com (MS Ian) wrote:

Hi all,

Stupid question...can a normal barcode scanner scan from an LCD
display displaying a barcode (instead of from scanning from paper and
ink)?


Cheers,
Ian

You might do it with the CCD type if you are very lucky, but definitely not with the
laser type.

 

[Bob Myers]

"John Fields" <jfields@austininstruments.com> wrote in message
news:upfle054pcrmn6f98tp0ti18d0gg9994oo@4ax.com...

Stupid question...can a normal barcode scanner scan from an LCD
display displaying a barcode (instead of from scanning from paper and
ink)?

---
If the barcode is being displayed statically, then I think there's a
pretty good chance you could scan it and get back the data you're
looking for. If its being multiplexed, then I think you'll get
garbage back.

I'm guessing the multiplexing or lack thereof is only one
concern. Are we talking about a simple reflective LCD here,
or an active-matrix backlit type (like most monitors or notebook
displays). If the latter - then given the way most barcode scanners
work (i.e., scan a light beam, often a low-power laser, across the
barcode and watch for variations in the reflected light), I think this
may be a pretty hit-or-miss proposition. There's no reason to
think that the LCD is going to reflect significantly more of the
light in those areas that appear lit up to the eye than it will in
the "dark" areas.

Even in the case of the simple reflective LCD, the basic effect
utilized by the display is often strongly wavelength-dependent -
it's still not a sure thing. Can't say more since I've never tried
it.

Bob M.

 

[John Fields]

On Tue, 06 Jul 2004 19:01:54 GMT, "Bob Myers"
<nospamplease@address.invalid> wrote:

"John Fields" <jfields@austininstruments.com> wrote in message
news:upfle054pcrmn6f98tp0ti18d0gg9994oo@4ax.com...
Stupid question...can a normal barcode scanner scan from an LCD
display displaying a barcode (instead of from scanning from paper and
ink)?

---
If the barcode is being displayed statically, then I think there's a
pretty good chance you could scan it and get back the data you're
looking for. If its being multiplexed, then I think you'll get
garbage back.

I'm guessing the multiplexing or lack thereof is only one
concern. Are we talking about a simple reflective LCD here,
or an active-matrix backlit type (like most monitors or notebook
displays). If the latter - then given the way most barcode scanners
work (i.e., scan a light beam, often a low-power laser, across the
barcode and watch for variations in the reflected light), I think this
may be a pretty hit-or-miss proposition. There's no reason to
think that the LCD is going to reflect significantly more of the
light in those areas that appear lit up to the eye than it will in
the "dark" areas.

Even in the case of the simple reflective LCD, the basic effect
utilized by the display is often strongly wavelength-dependent -
it's still not a sure thing. Can't say more since I've never tried

---
Since the active-matrix backlit types are, I believe, universally
muxed, they'll be automatically ruled out. What'll be left then, will
be transmissive, transflective, and reflective dot matrix and
character based displays. All dot matrix will then go away, since
they're muxed, and so will all of the muxed character based displays,
so we'll be left with statically driven transmissive, transflective,
and reflective character based displays. Of the three, the
transmissive types contain no reflector, so we'll be left with
transflective and reflective displays. transflective can be either
backlit or depend on external light, or both, for the source of
illumination, and reflective depends on external light. Of the two,
the reflective will give a better contrast ratio and will therefore be
more likely to work properly as a target for a scanner.

As far as wavelength dependency goes, I just illuminated a reflective
display with red light in an otherwise totally dark room and the
contrast between light and dark segments was excellent, so I don't
expect a scanner with a red laser diode would have much trouble
differentiating between the light and dark ares of the bar code
either.

I've fooled around with using LCD's for optical attenuators and there
are no color problems until you get down to IR, and then the rules
change.

--
John Fields

 

[Bob Masta]

On Tue, 06 Jul 2004 10:06:25 -0500, John Fields
<jfields@austininstruments.com> wrote:

On 6 Jul 2004 06:42:22 -0700, msian@canada.com (MS Ian) wrote:

Hi all,

Stupid question...can a normal barcode scanner scan from an LCD
display displaying a barcode (instead of from scanning from paper and
ink)?

---
If the barcode is being displayed statically, then I think there's a
pretty good chance you could scan it and get back the data you're
looking for. If its being multiplexed, then I think you'll get
garbage back.

Is muxing really likely to be a problem? My understanding
is that although the drive is muxed, the slow response
of the liquid crystals themselves means that they are
essentially static. (Unlike, for example muxed LEDs that
really do flash at the mux rate.)

I'd be more concerned about the reflectivity issues, but
this topic begs for a hands-on test.



Bob Masta
dqatechATdaqartaDOTcom

D A Q A R T A
Data AcQuisition And Real-Time Analysis
www.daqarta.com

 

[Bob Myers]

"John Fields" <jfields@austininstruments.com> wrote in message
news:ro7me0lgud272h2icmj2denra0v124rpg9@4ax.com...

Since the active-matrix backlit types are, I believe, universally
muxed, they'll be automatically ruled out.

Actually, they're not - that's the whole point of the active-
matrix drive scheme (yes, they're multiplexed in terms of
the row drive, but the point of the TFT is to hold the pixel in the
desired state during the entire frame time). I included them
since it seemed to be reasonable from the standpoint of the
original question - that someone might be attempting to scan
a barcode as displayed on, say, an LCD monitor.

What'll be left then, will
be transmissive, transflective, and reflective dot matrix and
character based displays. All dot matrix will then go away, since
they're muxed, and so will all of the muxed character based displays,
so we'll be left with statically driven transmissive, transflective,
and reflective character based displays.

So how would you plan to display a barcode on a
character-based display in the first place?


Bob M.

 

[John Fields]

On Wed, 07 Jul 2004 19:05:19 GMT, "Bob Myers"
<nospamplease@address.invalid> wrote:

"John Fields" <jfields@austininstruments.com> wrote in message
news:ro7me0lgud272h2icmj2denra0v124rpg9@4ax.com...
Since the active-matrix backlit types are, I believe, universally
muxed, they'll be automatically ruled out.

Actually, they're not - that's the whole point of the active-
matrix drive scheme (yes, they're multiplexed in terms of
the row drive, but the point of the TFT is to hold the pixel in the
desired state during the entire frame time). I included them
since it seemed to be reasonable from the standpoint of the
original question - that someone might be attempting to scan
a barcode as displayed on, say, an LCD monitor.

---
I don't recall that that was ever mentioned as a design criterion. You
might want to check the original post or get ahold of the OP to see
what he had in mind...
---

What'll be left then, will
be transmissive, transflective, and reflective dot matrix and
character based displays. All dot matrix will then go away, since
they're muxed, and so will all of the muxed character based displays,
so we'll be left with statically driven transmissive, transflective,
and reflective character based displays.

So how would you plan to display a barcode on a
character-based display in the first place?

---
That's simple. I know how to do it, and I can prove it, but I won't
divulge unless I got paid to do it.

But, the original question wasn't about what _I'd_ do to set up a
universal barcode scanning system, it was about how to detect bar
codes displayed on LCDs, and I think my response was reasonable, in
terms of actively scanning a statically displayed bar code.

Dynamically displayed? Either dictate or figure out the timing and
you've got it...


--
John Fields

 

[Bob Myers]

"John Fields" <jfields@austininstruments.com> wrote in message
news:cd1pe0lbm3i6j9ejeoei28e845h1p9j2am@4ax.com...

So how would you plan to display a barcode on a
character-based display in the first place?

---
That's simple. I know how to do it, and I can prove it, but I won't
divulge unless I got paid to do it.

Oh, I can think of several rather simple ways to do it,
but I guess I DO need to go back to the OP - I really
did have the impression that he or she was just thinking
of putting up a barcode on a standard LCD display, and
trying to scan it.

Bob M.

 

[MS Ian]

"Bob Myers" <nospamplease@address.invalid> wrote in message news:<yc1Hc.5487$Xa2.2511@news.cpqcorp.net>...

Oh, I can think of several rather simple ways to do it,
but I guess I DO need to go back to the OP - I really
did have the impression that he or she was just thinking
of putting up a barcode on a standard LCD display, and
trying to scan it.

Bob M.

Thanks guys for the feedback. Wow you guys really know your stuff!

And sorry for the confusion caused. I was just trying to determine if
I could scan a barcode displayed on my PalmPilot. Guess it is not
really feasible with the laser-type scanners.

Thanks again!

 

[the Wiz]

msian@canada.com (MS Ian) wrote:

Hi all,

Stupid question...can a normal barcode scanner scan from an LCD
display displaying a barcode (instead of from scanning from paper and
ink)?


Cheers,
Ian

From my experience with Palm PDAs, the answer is no.

Generating a valid 3 of 9 code on the Palm screen (non-backlit screens on Palm
III & m125), then trying to scan it with a Symbol 1500 series laser scanner does
not work.

Capturing the Palm screen and printing that image on paper scans perfectly.

I think the key here is the reflectivity of the Palm screen - shiny glass is
still shiny glass whether what's behind it is light gray or dark gray.

If you have a Palm device, the program is Code3of9 and can be downloaded
(including source) from this page: http://nsb.jecarter.com

John

More about me: http://www.jecarter.com/
VB3/VB6/C/PowerBasic source code: http://www.jecarter.com/programs.html
Freeware for the Palm with NS Basic source code: http://nsb.jecarter.com
Drivers for Pablo graphics tablet and JamCam cameras: http://home.earthlink.net/~mwbt/
Email here: http://www.jecarter.com/contactme.htm