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'[EE]: Calculator LCD repurposing?'
2006\01\02@201225 by Philip Pemberton

face picon face
Hi,
 I've just found a bag of calculator LCDs in my junkbox, complete with
zebra-strip connectors. Thing is, I have no idea what the pinouts of these
displays are. Has anyone here ever repurposed a calculator LCD to the point
of reversing the pinouts and hooking one up to, say, a PIC?

 If not, I'll see about reverse engineering the pinout at some point. I
guess the best method would be to generate a 3V 50Hz square wave to use as
the backplane signal, then feed it through an inverter to get the segment
signal. Then it's just a case of picking two pins and probing the display...
I suppose I'm going to have to mount it in front of a mirror or something,
unless anyone can think of another way to probe the contacts on the back of
the display while still being able to see the front of the display itself...

Thanks.
--
Phil.                              | Acorn RiscPC600 SA220 64MB+6GB 100baseT
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... I hate making predictions; especially about the future!

2006\01\03@084703 by andrew kelley

picon face
stick the thing in a vise to see the front when working on the back.. worked
for me..

andrew

2006\01\03@113845 by Philip Pemberton

face picon face

Eureka!

I've worked out the pinouts for the display. It has 27 pins, and seems to
have the segments and backplanes multiplexed three ways. Very odd...

I've put a quick-n-nasty diagram online at
<http://www.philpem.me.uk/blogfiles/calclcd.png>. Can someone please take a
quick look and tell me if it looks reasonably sane?

The display itself was marked "C1042". Another was marked "SUN 1-4", and yet
another was marked "SUN 4-4". The text is incredibly hard to read, owing to
the fact that it's been printed in the indium-tin-oxide (transparent
electrode) layer...

If anyone wants my "50Hz AC pulser" code, let me know and I'll post it. It
runs on a 12F675, but should also run fine on a 12F629. I had the circuit
running quite happily off a CR2032 :)

Thanks.
--
Phil.                              | Acorn RiscPC600 SA220 64MB+6GB 100baseT
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Nothing can go wroff001010    bus error: core dumped

2006\01\03@131610 by Peter

picon face


On Tue, 3 Jan 2006, Philip Pemberton wrote:

{Quote hidden}

Use a mains transformer with 6Vac output and use thin copper wire bent
as 'J's as probes. Tape the display to the table edge.

good luck,

Peter

2006\01\03@141357 by Peter

picon face


On Tue, 3 Jan 2006, Philip Pemberton wrote:

> I've worked out the pinouts for the display. It has 27 pins, and seems to
> have the segments and backplanes multiplexed three ways. Very odd...

Very common, you mean. You can drive such a display directly with
tristate outputs. Tristated outputs must be 'pulled' to the relevant
intermediate voltage with a resistor, each.

Peter

2006\01\03@165648 by Steve Smith

flavicon
face
Sounds like you now need to design a calculator to go with the glass !

Steve

-----Original Message-----
From: piclist-bouncesspamKILLspammit.edu [.....piclist-bouncesKILLspamspam.....mit.edu] On Behalf Of
Philip Pemberton
Sent: 03 January 2006 16:38
To: EraseMEpiclistspam_OUTspamTakeThisOuTmit.edu
Subject: Re: [EE]: Calculator LCD repurposing?


Eureka!

I've worked out the pinouts for the display. It has 27 pins, and seems to
have the segments and backplanes multiplexed three ways. Very odd...

I've put a quick-n-nasty diagram online at
<http://www.philpem.me.uk/blogfiles/calclcd.png>. Can someone please take a
quick look and tell me if it looks reasonably sane?

The display itself was marked "C1042". Another was marked "SUN 1-4", and yet
another was marked "SUN 4-4". The text is incredibly hard to read, owing to
the fact that it's been printed in the indium-tin-oxide (transparent
electrode) layer...

If anyone wants my "50Hz AC pulser" code, let me know and I'll post it. It
runs on a 12F675, but should also run fine on a 12F629. I had the circuit
running quite happily off a CR2032 :)

Thanks.
--
Phil.                              | Acorn RiscPC600 SA220 64MB+6GB 100baseT
philpemspamspam_OUTdsl.pipex.com              | Athlon64 3200+ A8VDeluxe R2 512MB+100GB
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Nothing can go wroff001010    bus error: core dumped

2006\01\03@180853 by Philip Pemberton

face picon face
In message <@spam@tdiv.lvafvKILLspamspamodls.cvpi.up>
         Peter <KILLspamplpKILLspamspamactcom.co.il> wrote:

> > I've worked out the pinouts for the display. It has 27 pins, and seems to
> > have the segments and backplanes multiplexed three ways. Very odd...
>
> Very common, you mean.

Now I've done some research, I will amend my previous statement. Common
indeed, just not with the segment/common wiring my LCD has. I've seen the
datasheet for Maxim's triplex display driver, but near as I can tell there's
no way to use it with these displays - the segment/common wiring is similar
in some places, but completely different in others.

> You can drive such a display directly with
> tristate outputs. Tristated outputs must be 'pulled' to the relevant
> intermediate voltage with a resistor, each.

So you keep the pins idled at about 2.5V and either pull high, low or float
them? Hm. Sounds like a plan, but it's going to need a fair few resistors...
Probably 27 (one for each segment/common) and two for the voltage divider.
Owch!

Thanks.
--
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... Which sparks some mnemonic circuitry.

2006\01\03@182454 by Robert Rolf

picon face
Philip Pemberton wrote:
{Quote hidden}

Or 27 resistors going to a single pin held at 2.5v (using an op amp).

Robert

2006\01\03@185937 by Philip Pemberton

face picon face
In message <RemoveME43BB07C6.8000303spamTakeThisOuTUAlberta.ca>
         Robert Rolf <Robert.RolfEraseMEspam.....ualberta.ca> wrote:

> Or 27 resistors going to a single pin held at 2.5v (using an op amp).

Or a PIC16F917 and three resistors. Roughly 30uA maximum current consumption
with INTRC clock, TMR1 @ 32kHz (ext xtal), and the CPU core spending most of
its time sleeping (with a huge processing burst every minute, and a brief
clock-update cycle roughly every second). I'll crunch the numbers later, but
it should be possible to halve the operating current and get the thing
running for a few years off a CR2032.

SHA-1 on a PIC16 could also be fun, especially with only a single INDF
pointer.

Sounds like I've got myself a new project :)

Thanks.
--
Phil.                              | Acorn RiscPC600 SA220 64MB+6GB 100baseT
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... Violence never solves anything, but it sure makes me feel good.

2006\01\03@235343 by William Chops Westfield

face picon face

>> Or 27 resistors going to a single pin held at 2.5v (using an op amp).
>>
Ah.  So THAT'S what an LCD driver actually does in a micro!  Lets the
third state of pins float at a different voltage.  From looking at
the external schematics of such things, it was clear that they were
getting a different voltage level, but I never quite connected that
with THREE possible output voltages...

BillW

2006\01\04@044802 by Alan B. Pearce

face picon face
>Sounds like I've got myself a new project :)

Certainly sounds like a display that could be used with one of the PICs that
are designed for LCD direct drive. IIRC from a query on the list in the last
couple of months, I got the impression that they are cable of multiplex LCD
drive, which it sounds like you need.

2006\01\04@054041 by Regulus Berdin

picon face
part 0 44 bytes
his is a multi-part message in MIME format.
part 1 607 bytes content-type:text/plain; charset=ISO-8859-1; format=flowed (decoded 7bit)

Philip Pemberton wrote:
> So you keep the pins idled at about 2.5V and either pull high, low or float
> them? Hm. Sounds like a plan, but it's going to need a fair few resistors...
> Probably 27 (one for each segment/common) and two for the voltage divider.
> Owch!

You only need 6 resistors, 2 for each backplanes if LCD is driven 1/2
bias.  Segments are driven either fully 1 or 0 so no need to 1/2 bias
them.  See attached timing diagram.

I had made a 7segment LCD controller with just few 74HC595 with an 8pin
PIC using this timing.

regards,
Reggie


part 2 13739 bytes content-type:image/gif; (decode)


part 3 35 bytes content-type:text/plain; charset="us-ascii"
(decoded 7bit)

2006\01\04@071354 by Philip Pemberton

face picon face
In message <RemoveME43BBA5E5.9050809EraseMEspamEraseMEgmail.com>
         Regulus Berdin <RemoveMERegulus.Berdinspam_OUTspamKILLspamgmail.com> wrote:

> You only need 6 resistors, 2 for each backplanes if LCD is driven 1/2
> bias.  Segments are driven either fully 1 or 0 so no need to 1/2 bias
> them.  See attached timing diagram.

That's a pretty neat way to do it. Only problem is, the display won't run in
SLEEP mode so I'm not going to be able to get the power consumption down far
enough to run it for long periods off a lithium coin cell. Still a neat idea,
though, and it might be worth a try...

So for three backplanes, the BP signals would look something like this:
      __
     |  |                       1
BP1 --+  +---------+  +--------  1/2
                  |__|          0
         __                    
        |  |                    1
BP2 -----+  +---------+  +-----  1/2
                     |__|       0
            __
           |  |                 1
BP3 --------+  +---------+  +--  1/2
                        |__|    0


In other words, 1/2 bias drive with 1/3 multiplexing.

Time for an experiment - just as soon as I find some of those zebra-strip
connectors that actually work...

Thanks.
--
Phil.                              | Acorn RiscPC600 SA220 64MB+6GB 100baseT
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... Another nearly-full box of Smarties!!

2006\01\04@073552 by Alan B. Pearce

face picon face
>Time for an experiment - just as soon as I find some
>of those zebra-strip connectors that actually work...

Go on eBay, and look for connectors for Nokia 8210 phones. It seems that the
originals were not a good design, and the replacements are supposed to be
better.

About £1  for a bag of 100, plus about £5-6 S&H IIRC (remember the [BUY]
thread ???)

2006\01\04@090852 by Philip Pemberton

face picon face
In message <000f01c6112b$643c09c0$EraseMEe7bdf682spamspamspamBeGonespace.rl.ac.uk>
         "Alan B. Pearce" <RemoveMEA.B.PearceKILLspamspamrl.ac.uk> wrote:

> Go on eBay, and look for connectors for Nokia 8210 phones. It seems that the
> originals were not a good design, and the replacements are supposed to be
> better.

Problem is they're only about an inch long; the contact area on this LCD is
about 2.5".
I've got a few dead HD44780 LCDs lying around - I can probably scavenge a few
zebra-strips from them. Then I just need to find some foam to put under the
LCD, and a piece of transparent plastic to put over the top to compress the
zebra-strip.

Thanks.
--
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... If I were you, who'd be me?

2006\01\04@093208 by Philip Pemberton

face picon face
In message <006e01c61113$f2b1b0a0$spamBeGonee7bdf682STOPspamspamEraseMEspace.rl.ac.uk>
         "Alan B. Pearce" <KILLspamA.B.PearcespamBeGonespamrl.ac.uk> wrote:

> Certainly sounds like a display that could be used with one of the PICs that
> are designed for LCD direct drive.

Certainly seems that way. Problem is, Farnell don't seem to stock any of the
Flash PICs that have onboard LCDCs. I've ended up ordering the 16F917s from
Microchip as samples, which I really didn't want to do...

> IIRC from a query on the list in the last
> couple of months, I got the impression that they are cable of multiplex LCD
> drive, which it sounds like you need.

That's what the datasheet says, anyway. Up to four commons (backplanes) and
24 segments IIRC.

Thanks.
--
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2006\01\04@093405 by Alan B. Pearce

face picon face
>> Go on eBay, and look for connectors for Nokia 8210 phones.
>
>Problem is they're only about an inch long; the contact
>area on this LCD is about 2.5".

I wouldn't have thought that is a problem, just use several end stacked - at
worst you may need to put a bit of cling film or similar between them for
insulation if the very end has a conductive stripe in it.

That is one of the reasons I figured these would be so good - there is so
many in the packet that there would be heaps to play with.

2006\01\04@192416 by Regulus Berdin

picon face
Philip Pemberton wrote:
> That's a pretty neat way to do it. Only problem is, the display won't run in
> SLEEP mode so I'm not going to be able to get the power consumption down far
> enough to run it for long periods off a lithium coin cell. Still a neat idea,
> though, and it might be worth a try...
Yes, consumption is a problem. Better to use an external LCD driver or a
PIC16F913/4/6/7 directly.


{Quote hidden}

Exactly.

regards,
Reggie

2006\01\04@193439 by Peter

picon face

On Tue, 3 Jan 2006, Philip Pemberton wrote:

{Quote hidden}

Use 4 8x1 resistor rows and an opamp as driver for the false 'ground'.
It is better if you simulate the 3-phase LCD drive using some graphical
tool, otherwise you will have trouble understanding it (ignore the phase
alternation in the beginning).

Peter

2006\01\04@194713 by Bob Blick

face picon face
> Philip Pemberton wrote:
>> That's a pretty neat way to do it. Only problem is, the display won't
>> run in
>> SLEEP mode so I'm not going to be able to get the power consumption down
>> far

If you have spare pins, you can use two pins per backplane and tristate
them when you want to sleep. Spare pins, yeah right, I know how rare that
is :)

Cheers,

Bob


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