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'High Current Serial Display Driver'
1999\11\12@094754 by Jack Shidemantle

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I would like to make a 9 (maybe 12) character display using incandescent
bulbs arranged in 7 segment format, so I could have 6 inch high characters.
This would of course be driven by a PIC providing RS232 output to the
display. Does anyone know of serial to parallel, or whatever it is I need,
drivers for this type application. Something that would take the serial
input and drive the appropriate segments of each character. I'm not
necessarily looking for a moving display just able to flash a few  words
one after another.

Thanks
Jack

1999\11\12@102601 by Reginald Neale

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>I would like to make a 9 (maybe 12) character display using incandescent
>bulbs arranged in 7 segment format, so I could have 6 inch high characters.
>This would of course be driven by a PIC providing RS232 output to the
>display. Does anyone know of serial to parallel, or whatever it is I need,
>drivers for this type application. Something that would take the serial
>input and drive the appropriate segments of each character. I'm not
>necessarily looking for a moving display just able to flash a few  words
>one after another.
>

 The Allegro UCN58xx series can do the serial-in, parallel-out
 part of it. They're stackable to as many outputs as you need.
 You have to do your own character generation, but that
 shouldn't be too difficult.

 Reg Neale

1999\11\12@105727 by Wagner Lipnharski

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Hello Jack, along with other several possible solutions,

1) take a look at:
http://www.marktechopto.com/tb62709f.htm it is a serial input (2+1
lines), decode, auto multiplex, common anode LED 7 seg, that can scan
and drive up to 4 displays.  As the segment is active low drive, and the
digit selection is high drive, you could use 8 PNP or P Channel FETS for
the segments and 4 NPN or N channel FET for the digit selection, to
drive your lamps. It has internal character generation and they can be
cascaded.

2) If your PIC has plenty of time, do the char generation and
multiplexing scan by yourself. Incandescent lamps have a nice
persistence for scanning. Try to use low voltage lamps. As it will be
multiplexed, probably you will want to use 12V lamps on 16, 18, 24 or
even 30Vdc (high peak pulses).  12V lamps requires higher current than a
power equivalent 110Vac lamps, so the filament is ticker, more
mechanical resistant and it is less sensible to multiplexing eye effect
(as the filament is ticker, it absorbs more heat, taking longer to cool
down).  If you apply power in 10Hz square wave to a regular 110Vac 40W
lamp, you probably will see some flickering, at the 12Vdc 40W lamp it is
not easily notice...

Wagner Lipnharski
UST Research Inc. - Orlando, Florida
-------------------------------------------------------
Free Classifieds? http://www.ustr.net/classifieds.shtml

1999\11\12@150154 by Jack Shidemantle

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Thanks Wagner, but now the project has grown as I talked it over with my
wife. Yes, it's a hobby project looking for an easy way to present a
christmas greeting (of course you have to do it electronically) to the
neighbors as they drive by. Now it really should be alpha-numeric. That
multiplys the complexity of this a whole bunch and I was struggling before.




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Hello Jack, along with other several possible solutions,

1) take a look at:
http://www.marktechopto.com/tb62709f.htm it is a serial input (2+1
lines), decode, auto multiplex, common anode LED 7 seg, that can scan
and drive up to 4 displays.  As the segment is active low drive, and the
digit selection is high drive, you could use 8 PNP or P Channel FETS for
the segments and 4 NPN or N channel FET for the digit selection, to
drive your lamps. It has internal character generation and they can be
cascaded.

2) If your PIC has plenty of time, do the char generation and
multiplexing scan by yourself. Incandescent lamps have a nice
persistence for scanning. Try to use low voltage lamps. As it will be
multiplexed, probably you will want to use 12V lamps on 16, 18, 24 or
even 30Vdc (high peak pulses).  12V lamps requires higher current than a
power equivalent 110Vac lamps, so the filament is ticker, more
mechanical resistant and it is less sensible to multiplexing eye effect
(as the filament is ticker, it absorbs more heat, taking longer to cool
down).  If you apply power in 10Hz square wave to a regular 110Vac 40W
lamp, you probably will see some flickering, at the 12Vdc 40W lamp it is
not easily notice...

Wagner Lipnharski
UST Research Inc. - Orlando, Florida
-------------------------------------------------------
Free Classifieds? http://www.ustr.net/classifieds.shtml

1999\11\12@202058 by John Mullan

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I have used the 5832 (high current 32 bit shift register).  You could shift in data for each bulb.  I'm imagining that you will use low voltage incandescents.  This driver chip can handle up to 24v (or there abouts).

Depending on number of lamps driven at any given time, you may need to drive the lamps using TIP30/31 or triacs if using AC.

John Mullan


{Original Message removed}

1999\11\12@204354 by Wagner Lipnharski

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John Mullan wrote:
>
> I have used the 5832 (high current 32 bit shift register).  You could shift in
data for each bulb.  I'm imagining that you will use low voltage incandescents.
 This driver chip can handle up to 24v (or there abouts).
>
> Depending on number of lamps driven at any given time, you may need to drive t
he lamps using TIP30/31 or triacs if using AC.
>
> John Mullan

... for a long and steady power switch to the lamps, a triac in AC is
ok, but not for multiplexing, since you can not turn it off faster than
16.6ms... remember, once it turns on, it will still on until the senoid
crosses zero.

It means, that if high speed shifting the 5832 with triacs at its
outputs, all triacs that receive a fast "1" bit when shifting will turn
its lamp on...and stay on for a minimum of 16.6ms... will be funny... :)

1999\11\13@234339 by Donald L Burdette

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You haven't mentioned what bulbs you intend to use, but I'm guessing you
want 1/4 or 1/2 watt bulbs.  At 12 Volts, that's about 20 or 40 mA per
bulb.  I'm also guessing you'll use a standard 5x7 matrix per character.
At 12 characters, that's 420 bulbs.  If worst case is 40% of bulbs on
(I'm guessing here!), that's 42 or 84 watts, and 3.5 or 7.0 amps.

While these numbers are not unreasonable, they are not trivial to work
with.

Multiplexing sounds great.  Since you'll have a 7x60 matrix, you'd have
60+7 drive pins to work with rather than 420.  However, I don't know that
a 1/60 duty cycle is reasonable for incandescent lamps.  I think you'd
want about 12*(60^0.5) = 93 volts drive (somebody correct me here if i'm
wrong).  Of course, at that voltage your average current would be less
than 1/2 or 1 amp.

If I were doing this, I think I'd go for 1/4 W bulbs, grouped into 4
groups of 3 characters.  That would give me a 28 x 15 matrix, and 1/15
duty cycle, requiring about 46.5 volt drive (round to 48?).  I'd use
74HC595 shift registers, 4 for rows and 2 for columns.  I'd make the rows
the low side, with a 1K resistor driving the base of a ZTX453 transistor.
Columns would be the high side, with ZTX553's, 1K resistor to a ZTX453
being driven by the '595 (see the current thread on high side drivers).
These parts are all available from Digi-Key.  Suitable substitutes could
be found easily.

My code would look kind of like this:

       Shift out 4 bytes to row drivers (each row is a full byte to make
software easier)
       Shift a 1 into first column driver
       Strobe the '595 output latch pins to update the output data
       Wait for 7 mS

       Shift out next 4 bytes for row drivers
       Shift the 1 to the next column driver
       Latch the outputs
       Wait 7 mS

       ...

This would give about 9.5 Hz refresh rate, which Wagner says is adequate.
You could trim the 7 mS down if you see flicker.

Let us know what you end up with!


Don

1999\11\15@083116 by Jack Shidemantle

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I plan on using 12V 500 ma bulbs and staying away from triacs.



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John Mullan wrote:
>
> I have used the 5832 (high current 32 bit shift register).  You could
shift in data for each bulb.  I'm imagining that you will use low voltage
incandescents.  This driver chip can handle up to 24v (or there abouts).
>
> Depending on number of lamps driven at any given time, you may need to
drive the lamps using TIP30/31 or triacs if using AC.
>
> John Mullan

... for a long and steady power switch to the lamps, a triac in AC is
ok, but not for multiplexing, since you can not turn it off faster than
16.6ms... remember, once it turns on, it will still on until the senoid
crosses zero.

It means, that if high speed shifting the 5832 with triacs at its
outputs, all triacs that receive a fast "1" bit when shifting will turn
its lamp on...and stay on for a minimum of 16.6ms... will be funny... :)

1999\11\15@084548 by Jack Shidemantle

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I was thinking about using 12V  4 or 7 watt bulbs but, you're right that
adds up to a lot of power in a hurry. If 40% were on using 7 watt bulbs
that would be 1176 watts using a 5 x 7 matrix! Think I better scale this
down and do some experimentation to see what bulb size I really need. I
want the display easily readable from a distance of 50 - 75 feet at night
(I think the night part will help a bunch).  Thanks for giving me a start
on this, will probably be back with more questions since I'm fairly new to
the software end of PICs.




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                   11/13/99 11:43
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You haven't mentioned what bulbs you intend to use, but I'm guessing you
want 1/4 or 1/2 watt bulbs.  At 12 Volts, that's about 20 or 40 mA per
bulb.  I'm also guessing you'll use a standard 5x7 matrix per character.
At 12 characters, that's 420 bulbs.  If worst case is 40% of bulbs on
(I'm guessing here!), that's 42 or 84 watts, and 3.5 or 7.0 amps.

While these numbers are not unreasonable, they are not trivial to work
with.

Multiplexing sounds great.  Since you'll have a 7x60 matrix, you'd have
60+7 drive pins to work with rather than 420.  However, I don't know that
a 1/60 duty cycle is reasonable for incandescent lamps.  I think you'd
want about 12*(60^0.5) = 93 volts drive (somebody correct me here if i'm
wrong).  Of course, at that voltage your average current would be less
than 1/2 or 1 amp.

If I were doing this, I think I'd go for 1/4 W bulbs, grouped into 4
groups of 3 characters.  That would give me a 28 x 15 matrix, and 1/15
duty cycle, requiring about 46.5 volt drive (round to 48?).  I'd use
74HC595 shift registers, 4 for rows and 2 for columns.  I'd make the rows
the low side, with a 1K resistor driving the base of a ZTX453 transistor.
Columns would be the high side, with ZTX553's, 1K resistor to a ZTX453
being driven by the '595 (see the current thread on high side drivers).
These parts are all available from Digi-Key.  Suitable substitutes could
be found easily.

My code would look kind of like this:

       Shift out 4 bytes to row drivers (each row is a full byte to make
software easier)
       Shift a 1 into first column driver
       Strobe the '595 output latch pins to update the output data
       Wait for 7 mS

       Shift out next 4 bytes for row drivers
       Shift the 1 to the next column driver
       Latch the outputs
       Wait 7 mS

       ...

This would give about 9.5 Hz refresh rate, which Wagner says is adequate.
You could trim the 7 mS down if you see flicker.

Let us know what you end up with!


Don

1999\11\15@174502 by paulb

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Donald L Burdette wrote:

> Multiplexing sounds great.  Since you'll have a 7x60 matrix, you'd
> have 60+7 drive pins to work with rather than 420.  However, I don't
> know that a 1/60 duty cycle is reasonable for incandescent lamps.

 It isn't, but then you've got it back to front.  The multiplex for a
7 row by 60 column display is only one in *seven*.  The calculation for
drive voltage is thus much more modest also.

 While in terms of the number of drivers, your alternate suggestion of
28 x 15 is logical, there is much to be said for multiplexing long rows.

 You should be able (if the cost is reasonable) to use integrated
drivers such as the TPIC6595 mounted on the individual modules to drive
the rows at quite modest voltage, while using only seven power
transistors to drive the columns at relatively high current.  These rows
of course chain from one module to the next.

 Don't forget the diode for each incandescent lamp!
--
 Cheers,
       Paul B.

1999\11\16@142227 by Larry G. Nelson Sr.

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Super bright LEDs may do what you want. I have a sign being used for race
tracks that is used day and night and is very visible. Take a look at my
web site to see what it looks like. I have 2 incandescent lamps on the top
that I blink to gain attention. 4 LEDs in series for each segment in the 7
segment displays.


At 01:43 PM 11/15/99 GMT, you wrote:
{Quote hidden}

Serial
{Quote hidden}

Larry G. Nelson Sr.
EraseMEL.Nelsonspam_OUTspamTakeThisOuTieee.org
http://www.ultranet.com/~nr

1999\11\16@162726 by Jack Shidemantle

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Thanks Larry, haven't been able to get at your site yet, but I began to
think the same way. After reading the posts on LED traffic signals and
remembering how many vehicles use LED's as the third stop light, that may
indeed be the way to go. It would sure keep the drive power down to more
reasonable levels. Need to work out the logic yet as I am very
inexperienced on the software side.

Thanks also to the rest of the replys out there. This project may take me a
while to implement.




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                   11/15/99 04:19
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Super bright LEDs may do what you want. I have a sign being used for race
tracks that is used day and night and is very visible. Take a look at my
web site to see what it looks like. I have 2 incandescent lamps on the top
that I blink to gain attention. 4 LEDs in series for each segment in the 7
segment displays.


At 01:43 PM 11/15/99 GMT, you wrote:
{Quote hidden}

Serial
{Quote hidden}

Larry G. Nelson Sr.
RemoveMEL.NelsonTakeThisOuTspamieee.org
http://www.ultranet.com/~nr

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