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'Scoreboard'
1997\11\21@095108 by Andy Tucker

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I am looking for the person wanting some information on scoreboards
I have located someone who maintanes the sysyems in our county and
he said he would like to help.

Please E-mail me at spam_OUTrtuckerTakeThisOuTspamscci.net

Andy Tucker

1997\11\30@230852 by Troy Powledge

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part 0 390 bytes
-----Original Message-----
From:   Andy Tucker [SMTP:.....rtuckerKILLspamspam@spam@SCCI.NET]
Sent:   Friday, November 21, 1997 7:42 AM
To:     PICLISTspamKILLspamMITVMA.MIT.EDU
Subject:        Scoreboard

I am looking for the person wanting some information on scoreboards
I have located someone who maintanes the sysyems in our county and
he said he would like to help.

Please E-mail me at .....rtuckerKILLspamspam.....scci.net

Andy Tucker


'Scoreboard'
1997\12\01@170600 by Andrew Mayo
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A standard 5 X 8 scrolling LED display typically has 8 rows of maybe 60
or more LEDs per row. A single bank of shift registers followed by
darlington drivers is connected to the cathodes of the LED columns. The
LED rows are driven by 8 PNP darlington transistors (high-side drivers).
The dot pattern is shifted into the shift registers, and strobed to the
output latches, and this process overlaps the display of the previous
(latched) row. Each row is displayed for about 10mS. High-brightness
LEDs (1000mCd or more) are recommended. Some designs pulse the LEDs at
high currents. I recommend running them around 20mA each, otherwise
intermittent LED and driver failures are likely to occur. The software
is quite intricate to design, I can assure you.

Lightbulbs are driven in a similar way but respond more slowly, of
course, and should have pre-heat current applied even when nominally
off, to avoid thermal shock from destroying the bulb.

{Quote hidden}

>       {Original Message removed}

1997\12\02@160939 by John Payson

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> Lightbulbs are driven in a similar way but respond more slowly, of
> course, and should have pre-heat current applied even when nominally
> off, to avoid thermal shock from destroying the bulb.

Note that because lightbulbs are not diodes, current may flow through
unexpected paths; your best bet is probably to try to bias inactive
rows at 1/3 voltage and inactive columns at 2/3 voltage; this will ensure
that all the inactive lights are at 1/3 voltage (regardless of what else
is on the same row/column).  Note that if the lights only get 1/3 voltage
they will be using only about 1/9 the power of "full on" lights and will
consequently glow much more dimly (if at all).

1997\12\03@004104 by Mike Keitz

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On Tue, 2 Dec 1997 13:04:32 -0600 John Payson <KILLspamsupercatKILLspamspamMCS.NET> writes:
>> Lightbulbs are driven in a similar way but respond more slowly, of
>> course, and should have pre-heat current applied even when nominally
>> off, to avoid thermal shock from destroying the bulb.
>
>Note that because lightbulbs are not diodes, current may flow through
>unexpected paths; your best bet is probably to try to bias inactive
>rows at 1/3 voltage and inactive columns at 2/3 voltage; this will
>ensure
>that all the inactive lights are at 1/3 voltage (regardless of what
>else
>is on the same row/column).  Note that if the lights only get 1/3
>voltage
>they will be using only about 1/9 the power of "full on" lights and
>will
>consequently glow much more dimly (if at all).


Light bulbs aren't diodes, and they aren't resistors either.  A bulb that
is hot enough to glow acts more closely to a constant-current source.  So
bulbs with 1/3 full voltage will have a lower resistance than if they had
full rated voltage, and would absorb more than 1/9 the rated power.

The best bet is a diode in series with each bulb.  Of course, the diodes
then represent another failure point.  Also, operating bulbs at even
slightly less than rated voltage gives much longer life.  This is good
when hundred or thousands of bulbs are involved.

I suspect some of the existing designs use SCRs for row and/or column
drive.  Using SCRs for both would of course restrict the multiplexing
time to half-cycles of the power line.  If they are just the row drivers
(from a DC supply rail), then turning all the columns off would cause the
SCR to turn off and another row could be selected.

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