large led display
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I need an education on LEDs. I am building an 8" digital display using
seven digits with 20 LEDs per each of the seven segments (140 LEDs per
digit) and using a MAX7219 driver. Should I wire the LEDs in serial or
parallel and what power supply should I be using? I have read the data
sheets on the 7219 but don't want to smoke anything. Thanks, Dan
seven digits with 20 LEDs per each of the seven segments (140 LEDs per
digit) and using a MAX7219 driver. Should I wire the LEDs in serial or
parallel and what power supply should I be using? I have read the data
sheets on the 7219 but don't want to smoke anything. Thanks, Dan
Comments
Max7219 would not be able to provide. Your best bet is to either
hook up a Quad Darlington type line driver (DigiKey TD62783AF-ND) (or
sink driver depending on you display), or use a latch type IC like
the UCN5821 serial drivers. This one is rather easy as you send the
Binary data directly to the chip (each controls 8 segments - that
means you will have to have as many UCNs as you have Digits) and
wouldn't have to update the data all the time like the MAX does.
Al
--- In basicstamps@y..., daniel.d.dangremond@j... wrote:
> I need an education on LEDs. I am building an 8" digital display
using
> seven digits with 20 LEDs per each of the seven segments (140 LEDs
per
> digit) and using a MAX7219 driver. Should I wire the LEDs in
serial or
> parallel and what power supply should I be using? I have read the
data
> sheets on the 7219 but don't want to smoke anything. Thanks, Dan
> I need an education on LEDs. I am building an 8" digital display
using
> seven digits with 20 LEDs per each of the seven segments (140 LEDs
per
> digit) and using a MAX7219 driver. Should I wire the LEDs in
serial or
> parallel and what power supply should I be using? I have read the
data
> sheets on the 7219 but don't want to smoke anything. Thanks, Dan
Dan, you have an interesting problem here. If you hook them in
parallel, you will find that you need 20 LEDs x 20 ma each = .4 amps
per segment, or almost 20 amps of total power if you don't multiplex
them somehow. Even multiplexing the 7 segments you need almost 3 amps.
Multiplexing adds a lot of complexity - I don't think you can use a
single chip solution like the 7219 due to the current requirements.
On the other hand, if you put them in series, you need about 30 volts
to operate each segment (1.5 v per LED x 20). You need to check the
forward voltage drop of the specific LEDs to see what the total
voltage will be.
I think I would try to put them in series and look at using a chip
like the TI TPIC6B595 which is a serial shift register with a power
output stage. Each of these chips could operate 8 segments, but I
would hook each one to a single digit (simpler to do the software
that way) - so you'd need 7 of them connected in a chain to operate
the 7 digits. I think they're good up to about 35 volts, so they
barely meet the requirements, but they might be worth a try. You can
do one long shift to shift the 7 digit values into the chips. You'll
need a stable 35 volt power supply to hook this to, but only about
one amp (49 segments x 20 ma each). Actually, you can light the leds
with a lot less than 20 ma if you don't need max brightness, so maybe
half an amp would be plenty. You might consider whether you really
need 20 LEDs in a segment, or if you could get away with a smaller
number to keep the voltage down.
Too bad you don't need just 6 digits - we have a board available that
drives 6 of these chips (48 outputs) from a simple serial input. For
$100 it's a ready made solution, but you need 49 outputs, not 48,
actually 56 if you group them by one digit per chip.
Chuck
http://dbserv.maxim-ic.com/quick_view2.cfm?pdf_num=1339
I would suggest wiring each segment's led's in parallel and putting a
series resistor for each LED in this segment, to control it's current.
I would suggest a value somewhere between 25 - 150 ohm. I would be
temped to try the circuit without this resistor, because it's probably
not needed, just wire them in parallel.
The power supply should be 5 volts and the resistor between pins 18-19
of the 7219 controls the current through the LED's.
regards,
Leroy
daniel.d.dangremond@j... wrote:
>
> I need an education on LEDs. I am building an 8" digital display using
> seven digits with 20 LEDs per each of the seven segments (140 LEDs per
> digit) and using a MAX7219 driver. Should I wire the LEDs in serial or
> parallel and what power supply should I be using? I have read the data
> sheets on the 7219 but don't want to smoke anything. Thanks, Dan
>
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>
>
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> I need an education on LEDs. I am building an 8" digital display
using
> seven digits with 20 LEDs per each of the seven segments (140 LEDs
per
> digit) and using a MAX7219 driver. Should I wire the LEDs in
serial or
> parallel and what power supply should I be using? I have read the
data
> sheets on the 7219 but don't want to smoke anything. Thanks, Dan
I rechecked the data sheet on the TPIC6B595 - it is rated 50 volts at
150 milliamps, which should be plenty for 20 LEDs in series. You will
still need a resistor in series with each string of LEDs, but I think
you will have to find the value that works experimentally - it will
depend a lot on the power supply voltage you are working with and the
exact voltage drop across the string of LEDs. I would start with 1K
or more and work my way lower until I got the current to be about 15
ma or so. You may even want to put a pot in series with each string
so you can adjust each segment to be equal brightness.
Note - voltages above 48 volts are considered dangerous and need to
be protected from human contact. Whatever you use for a power supply
needs to be well regulated so it stays below this level.
Chuck
shocked!! I think somebody here is in for a rude awaking!! You really
need to listen to the advice of someone who will guarantee their
design. Hate to see you get hurt! The chip selected, max. 7219 was not
designed for this kind of service! You may need to investigate some
higher voltage high side & Low side voltage current drivers. See
Digi-key.com.
Leroy
Chuck Davis wrote:
>
> --- In basicstamps@y..., daniel.d.dangremond@j... wrote:
> > I need an education on LEDs. I am building an 8" digital display
> using
> > seven digits with 20 LEDs per each of the seven segments (140 LEDs
> per
> > digit) and using a MAX7219 driver. Should I wire the LEDs in
> serial or
> > parallel and what power supply should I be using? I have read the
> data
> > sheets on the 7219 but don't want to smoke anything. Thanks, Dan
>
> I rechecked the data sheet on the TPIC6B595 - it is rated 50 volts at
> 150 milliamps, which should be plenty for 20 LEDs in series. You will
> still need a resistor in series with each string of LEDs, but I think
> you will have to find the value that works experimentally - it will
> depend a lot on the power supply voltage you are working with and the
> exact voltage drop across the string of LEDs. I would start with 1K
> or more and work my way lower until I got the current to be about 15
> ma or so. You may even want to put a pot in series with each string
> so you can adjust each segment to be equal brightness.
>
> Note - voltages above 48 volts are considered dangerous and need to
> be protected from human contact. Whatever you use for a power supply
> needs to be well regulated so it stays below this level.
>
> Chuck
>
> To UNSUBSCRIBE, just send mail to:
> basicstamps-unsubscribe@yahoogroups.com
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of the message will be ignored.
>
>
> Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
OK, this time I really am going back to the PIClist for a while...
before I go however, I am tempted to say more, but I will actually apply the
old proverb here:
"The wise man is one of few words" - And I'm not talking about myself...
C
>
Original Message
> From: Leroy Hall [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=Ht4VdMUavQ5sFiqY9jaWUI_SvH1diYnc3E1I-7XZaV0DWZSUg6uFPMDdZ7oJqEsxHyB5rsugxPXe]leroy@f...[/url
> Sent: Wednesday, November 14, 2001 10:39 AM
> To: basicstamps@yahoogroups.com
> Subject: Re: [noparse][[/noparse]basicstamps] Re: large led display
>
>
> I don't think I would touch 40 volts much less 47, unless I
> wanted to be
> shocked!! I think somebody here is in for a rude awaking!!
> You really
> need to listen to the advice of someone who will guarantee their
> design. Hate to see you get hurt! The chip selected, max.
> 7219 was not
> designed for this kind of service! You may need to investigate some
> higher voltage high side & Low side voltage current drivers. See
> Digi-key.com.
>
> Leroy
>
> Chuck Davis wrote:
> >
> > --- In basicstamps@y..., daniel.d.dangremond@j... wrote:
> > > I need an education on LEDs. I am building an 8" digital display
> > using
> > > seven digits with 20 LEDs per each of the seven segments (140 LEDs
> > per
> > > digit) and using a MAX7219 driver. Should I wire the LEDs in
> > serial or
> > > parallel and what power supply should I be using? I have read the
> > data
> > > sheets on the 7219 but don't want to smoke anything. Thanks, Dan
> >
> > I rechecked the data sheet on the TPIC6B595 - it is rated
> 50 volts at
> > 150 milliamps, which should be plenty for 20 LEDs in
> series. You will
> > still need a resistor in series with each string of LEDs,
> but I think
> > you will have to find the value that works experimentally - it will
> > depend a lot on the power supply voltage you are working
> with and the
> > exact voltage drop across the string of LEDs. I would start with 1K
> > or more and work my way lower until I got the current to be about 15
> > ma or so. You may even want to put a pot in series with each string
> > so you can adjust each segment to be equal brightness.
> >
> > Note - voltages above 48 volts are considered dangerous and need to
> > be protected from human contact. Whatever you use for a power supply
> > needs to be well regulated so it stays below this level.
> >
> > Chuck
> >
> > To UNSUBSCRIBE, just send mail to:
> > basicstamps-unsubscribe@yahoogroups.com
> > from the same email address that you subscribed. Text in
> the Subject and Body of the message will be ignored.
> >
> >
> > Your use of Yahoo! Groups is subject to
> http://docs.yahoo.com/info/terms/
>
>
> To UNSUBSCRIBE, just send mail to:
> basicstamps-unsubscribe@yahoogroups.com
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> Subject and Body of the message will be ignored.
>
>
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> http://docs.yahoo.com/info/terms/
>
>
> I don't think I would touch 40 volts much less 47, unless I wanted
to be shocked!! I think somebody here is in for a rude awaking!!
You really need to listen to the advice of someone who will guarantee
their design. Hate to see you get hurt! The chip selected, max.
7219 was not designed for this kind of service! You may need to
investigate some higher voltage high side & Low side voltage current
drivers. See Digi-key.com.
> Leroy
I stand corrected! Don't want to see anyone get zapped. ;-)
Actually, I like Peter's suggestion a lot better - combination of
serial and parallel circuits - current goes up some, but voltage goes
down. You could probably run the whole thing off a 13.8 volt power
supply like they sell at Radio Shack.
Chuck
You use 20 leds per segment.
I would wire the leds 4 in parallel, and so 5 sets in series with a small
resistor.
The total current per segment would be about 4x10mA=40mA
The total voltage required across the leds would be 5x2,2V=11V.
Using a 12V supply gives you (12V-11V)/40mA ~ 22 ohm for the resistor.
The above applies to each segment. The 7219 cannot handle 12V directly
I believe, but you could use ULN2803A darlington drivers.
Regards peter.
Oorspronkelijk bericht
Van: Chuck Davis [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=zSDZfP89vnV6EHmWnqX2gMdf0Zk_IIBd7Aj2kT7PMWm4HWRNnQOSgBOYXP0T_7uYAy0Ic8E-DkBDO1ITDdoVukrR]cdavis@o...[/url
Verzonden: woensdag 14 november 2001 5:57
Aan: basicstamps@yahoogroups.com
Onderwerp: [noparse][[/noparse]basicstamps] Re: large led display
--- In basicstamps@y..., daniel.d.dangremond@j... wrote:
> I need an education on LEDs. I am building an 8" digital display
using
> seven digits with 20 LEDs per each of the seven segments (140 LEDs
per
> digit) and using a MAX7219 driver. Should I wire the LEDs in
serial or
> parallel and what power supply should I be using? I have read the
data
> sheets on the 7219 but don't want to smoke anything. Thanks, Dan
I rechecked the data sheet on the TPIC6B595 - it is rated 50 volts at
150 milliamps, which should be plenty for 20 LEDs in series. You will
still need a resistor in series with each string of LEDs, but I think
you will have to find the value that works experimentally - it will
depend a lot on the power supply voltage you are working with and the
exact voltage drop across the string of LEDs. I would start with 1K
or more and work my way lower until I got the current to be about 15
ma or so. You may even want to put a pot in series with each string
so you can adjust each segment to be equal brightness.
Note - voltages above 48 volts are considered dangerous and need to
be protected from human contact. Whatever you use for a power supply
needs to be well regulated so it stays below this level.
Chuck
To UNSUBSCRIBE, just send mail to:
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For 13.8V the series resistor is about 68 ohms (0.1watt at 40mA).
As the 7219 multiplexes no more than one digit is lit at a time
so the required current would be 8x40mA=320mA to lit 8 segments.
A 13.8V 1A power supply should be sufficient for the leds.
Regards peter
Oorspronkelijk bericht
Van: Chuck Davis [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=aInUX8rOUtdlnsEKc1XNaGw25Iqa49z9YP-2IvmHIT3545TEeDHAfaqa7SpssyaDOOQoBa02o8cS5aab4P-F]cdavis@o...[/url
Verzonden: woensdag 14 november 2001 12:55
Aan: basicstamps@yahoogroups.com
Onderwerp: [noparse][[/noparse]basicstamps] Re: large led display
--- In basicstamps@y..., Leroy Hall <leroy@f...> wrote:
> I don't think I would touch 40 volts much less 47, unless I wanted
to be shocked!! I think somebody here is in for a rude awaking!!
You really need to listen to the advice of someone who will guarantee
their design. Hate to see you get hurt! The chip selected, max.
7219 was not designed for this kind of service! You may need to
investigate some higher voltage high side & Low side voltage current
drivers. See Digi-key.com.
> Leroy
I stand corrected! Don't want to see anyone get zapped. ;-)
Actually, I like Peter's suggestion a lot better - combination of
serial and parallel circuits - current goes up some, but voltage goes
down. You could probably run the whole thing off a 13.8 volt power
supply like they sell at Radio Shack.
Chuck
To UNSUBSCRIBE, just send mail to:
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