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'Scoreboard [OT]'
1997\12\01@002014 by Michael Coop (pjm)

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Try looking at display drivers for alphanumeric LED displays - this should
give you a good idea where to start.

The most common displays are arranged as a 5 columns x7 rows matrix, and
there are chips designed to specifically drive these displays, or for a
more economical approach to large displays, you may consider treating the
display as 'blocks' of perhaps 8x8 pixels.

Then, you can address the columns directly, or use a shift register to
'walk' along the columns one at a time, while you send 8 bits at a time to
turn the lamps on in each column as desired.

Of course you need to keep in mind the refresh rate and power available for
your particular application.

Regards
MC

On Monday, December 01, 1997 3:35 AM, Troy Powledge [SMTP:spam_OUTtpowTakeThisOuTspameramp.net]
wrote:
> Are we talking about the type of score boards that you see outside of
banks that display time and temp with light bulbs for pixels? If so I would
like to know how all of the individual pixels are controlled. They have to
be multiplexed some how. Any information about the system would be
appreciated.
{Quote hidden}

1997\12\01@095451 by **NERI**

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!DOCTYPE HTML PUBLIC "-//W3C//DTD W3 HTML 3.2//EN">

Andy:

Your discussion of the multiplexing of columns in a large scoreboard is understandable. I use 16 of the 7x5 red displays in a scoreboard I've designed. But do you know a method in which you do the same thing with 7x5 displays with bicolor LEDs? ( Red, Green and Yellow also) .I think the hardware would become a lot more complicated.

Any suggestions would be appreciated.

-- Neri.

 


From: Michael Coop (pjm) <mcoop@POP.JARING.MY>
To: PICLIST@MITVMA.MIT.EDU
Date: Lunes, Diciembre 01, 1997 1:21 AM
Subject: Re: Scoreboard [OT]


Troy,

Try looking at display drivers for alphanumeric LED displays - this should
give you a good idea where to start.

The most common displays are arranged as a 5 columns x7 rows matrix, and
there are chips designed to specifically drive these displays, or for a
more economical approach to large displays, you may consider treating the
display as 'blocks' of perhaps 8x8 pixels.

Then, you can address the columns directly, or use a shift register to
'walk' along the columns one at a time, while you send 8 bits at a time to
turn the lamps on in each column as desired.

Of course you need to keep in mind the refresh rate and power available for
your particular application.

Regards
MC

On Monday, December 01, 1997 3:35 AM, Troy Powledge [SMTP:tpow@eramp.net]
wrote:
> Are we talking about the type of score boards that you see outside of
banks that display time and temp with light bulbs for pixels? If so I would
like to know how all of the individual pixels are controlled. They have to
be multiplexed some how. Any information about the system would be
appreciated.
> Processor?
> Multiplex scheme?
> Software?
> Thanks,
> Troy Powledge
> TCo. Systems
>
> {Original Message removed}

1997\12\01@124523 by Mike Keitz

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On Mon, 1 Dec 1997 09:37:43 -0500 **NERI**
<EraseMEnllosatspam_OUTspamTakeThisOuTMAIL.COSAPIDATA.COM.PE> writes:

But do you know a method in which you do the same thing with
>=
>7x5 displays with bicolor LEDs? ( Red, Green and Yellow also) .I think
>=
>the hardware would become a lot more complicated.=20

If you use the LEDs with 3 leads, then the red and green sides share one
common lead (connected to the "row" driver), and there would be twice as
many "column" drivers,  half of them for all the reds (same as if the
matrix were just red LEDs) and more for the green sides.  Of course the
row drivers and the power supply would have to be capable of twice the
current if the red and green sides are to be turned on at the same time.

1997\12\01@181213 by Andrew Mayo

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Yes, it does get complex. I saw an amazing display at the ESPN bar in
Orlando recently that uses LEDs that can generate red, green and blue,
and consequently it could do red, orange, yellow, green,blue and violet.
Very slick.

If they are multi-terminal devices you need three shift registers and
cathode drivers, but still only 8 row drivers.

If you are using two-terminal red/green LEDs then the driver circuitry
is complex because it has to be able to switch a bipolar signal across
the LEDs. For yellow, you'd need to switch the signal rapidly, as well.
So I think multi-terminal devices would be far simpler to use.
Expensive, though.

{Quote hidden}

> > {Original Message removed}

1997\12\02@064513 by paulb

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Pardon me, I don't wish to be repetitious, but I posted a reply on
essentially the same thread last month:

Subject: Re: ADVICE ON PICs (Times Square Display)
Date: Mon, 17 Nov 1997 23:00:55 +1000

These have been a popular magazine project, and I actually have half
a dozen used commercial ones sitting in my garage waiting for reverse
engineering.  I did not get the programmer box, and their Lithium RAM
batteries are dead except for one, so there is no other choice.

 The array has a set of latched shift registers driving the columns,
and the rows are driven in turn, i.e., it is multiplexed by row.  A
complete set of row data is shifted in whilst the previous row is being
strobed, then the strobe is turned off, the data latched, and the next
row strobe is turned on.

 With 1 in 7 multiplexing, good brightness is obtained.  You will
probably need ULN drivers for the columns making two chips and 8
resistors per 8 columns or 10 chips per 8 7x5 modules.  You may get by
with a ULN driver for the rows as whilst they draw a heavy current (the
full supply current in fact), only one is ever enabled at once.

 The "plenty of I/O lines" requirement is debatable.  Three to select
the row via an HC138, one for serial data and one to latch makes five
lines to drive the display, add I2C bus, serial port and maybe Microwire
for temperature.  Using an I2C EEPROM for data storage, since it is only
read repeatedly, should work.  You might as well initialise it and use
it for the font also (i.e., download the font from the PC along with
the message!)  I have a suspicion you could do it with a PIC16F84.

**NERI** wrote:

> I use 16 of the 7x5 red displays in a scoreboard
> I've designed. But do you know a method in which you do the same thing
> with 7x5 displays with bicolor LEDs? ( Red, Green and Yellow also) I
> think the hardware would become a lot more complicated.

 The word is DOUBLE.  Either you duplicate the column data drivers
(shift registers) in the above schema using three pin bi-colour LEDs,
which is on consideration the cleanest approach, or you use two-pin
bi-colours and now need bipolar drivers on BOTH column data and row
select.

 The latter could be implemented with only a single shift register
driving the tri-state line of each individual column driver, the common
"data" line alternately selecting high and low data phases (red and
green).  Similarly, the row driver would enable a given row with a
"data" value complementary to the current row driver polarity.

 I tend to think it would be easier to have two shift register/ uni-
polar driver sets with three-pin LEDs, so that the multiplex duty cycle
is only 1/rows, but you could use one column driver set and two row
select sets alternately multiplexed (with of course, separate column
data sets latched in) with a 1/2*rows duty cycle as for the two-pin
LEDs.

 Clear as mud?

> From: Michael Coop (pjm) <mcoopEraseMEspam.....POP.JARING.MY>
> Date: Lunes, Diciembre 01, 1997 1:21 AM

> Try looking at display drivers for alphanumeric LED displays - this
> should give you a good idea where to start.

> The most common displays are arranged as a 5 columns x7 rows matrix,
> and there are chips designed to specifically drive these displays,

Three problems: How much?  Can they handle random data, particularly
laterally-shifted data as needed for scrolling, wide characters and
graphics; and how much multiplexing do you still need to load the data
into these chips?

> or for a more economical approach to large displays, you may consider
> treating the display as 'blocks' of perhaps 8x8 pixels.

 But then you would still need a processor to buffer the 8x8 block and
multiplex it separately.

> Then, you can address the columns directly, or use a shift register to
> 'walk' along the columns one at a time, while you send 8 bits at a
> time to turn the lamps on in each column as desired.

 If you are referring to multiplexing a 50- to 100- column display in
one block, you are going to have a VERY low duty cycle.  That is why as
I have outlined above, practical designs use shift registers to latch in
a whole ROW of however-many column pixels are needed and strobe that row
while the next row is shifted in.

 Cheers,
       Paul B.

1997\12\04@062420 by paulb

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Andrew Mayo wrote:

> Yes, it does get complex. I saw an amazing display at the ESPN bar in
> Orlando recently that uses LEDs that can generate red, green and blue,
> and consequently it could do red, orange, yellow, green,blue and
> violet.  Very slick.

 And white presumably?

> For yellow, you'd need to switch the signal rapidly, as well.

 Why "rapidly"?

 Looks like you beat me to the punch explaining the pros and cons of
how you strobe the things.  Sigh!  Never mind!

 Cheers,
       Paul B.

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