BS2 and led display
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Posts: 46,084
Hi!
I wonder if it is possible to connect a second 8 segment leddisplay to
bs2 without using all pins or the led driver circuit.
Regards
Robert
I wonder if it is possible to connect a second 8 segment leddisplay to
bs2 without using all pins or the led driver circuit.
Regards
Robert
Comments
can only drive 50 mA -- so if you don't drive
all the LED segments at the same time, this
can be done. Note each segment takes around
10 mA to light. But why do this?
A single $2.00 74HCT595 can easily drive all 8
segments, all at the same time, without
worrying about burning out a $50.00 BS2.
And what is this 'Second' LED display? Where
is the 'First' one?
--- In basicstamps@yahoogroups.com, "Robert Bohlin"
<robert.bohlin@b...> wrote:
>
> Hi!
>
> I wonder if it is possible to connect a second 8 segment leddisplay
to
> bs2 without using all pins or the led driver circuit.
>
> Regards
> Robert
Stamp pins you get eight outputs, and they can be daisy-chained if you
want to add more displays.
-- Jon Williams
-- Applications Engineer, Parallax
-- Dallas Office
Original Message
From: Robert Bohlin [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=TFwEG8nXzBgIu9Cvs66eZgtGkbKUHv3DXdVjMdTrrT0iPVFSuh0D4YDSnB384pVM2fuHCQZku39Q9c9qfM6AaHmmPJM]robert.bohlin@b...[/url
Sent: Wednesday, April 14, 2004 10:06 AM
To: basicstamps@yahoogroups.com
Subject: [noparse][[/noparse]basicstamps] BS2 and led display
Hi!
I wonder if it is possible to connect a second 8 segment leddisplay to
bs2 without using all pins or the led driver circuit.
Regards
Robert
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> bs2 without using all pins or the led driver circuit.
Sure, you only need to use one more pin to select which LED display you're
talking to. This pin will enable one and disable the other LED display. This
"trick" is call multiplexing. Two pins would allow you to select four LED's;
three pins, eight, etc. Note that the more LED's you're multiplexing the
less time that any one LED display will be illuminated. You can compensate
for this by increasing the available current thru an LED for the period that
it's enabled. Usually this is done by increasing the supply voltage to the
LED but you may be able to just decrease (or eliminate) the current limiting
resistors for each LED display.
For an example of an 8-digit LED display see:
<http://www.maxim-ic.com/images/DI217Fig01.gif>
Here's a PIC circuit that drives four LED displays:
<http://picbasic.com/resources/articles/ledart.htm>
Another: <http://www.doug.h.rice.btinternet.co.uk/countdown/>
Personally I'd consider the led driver circuit. These usually automatically
adjust the current to get a consistent brightness regardless of the number
of segments illuminated.
--
Enjoy,
George Warner,
Schizophrenic Optimization Scientists
Apple Developer Technical Support (DTS)
I am a little confused about the wiring, although I understand the
concept. I had students last semester experimenting with three to four 8
segments on a BOE and the wiring was a mess as well as the project. I
think it can be done though but I'm not sure. Could someone please
expand on this topic?
Mark
Original Message
From: George Warner [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=8MZYQMineX15l84cKROWGLu0WGbh1s8IGctJwZS6wmshOX3uqh3ZOpcP06zCt5VbUvISQjex3Q]geowar@a...[/url
Sent: Thursday, April 15, 2004 1:49 AM
To: basicstamps@yahoogroups.com
Cc: Robert Bohlin
Subject: [noparse][[/noparse]basicstamps] re: BS2 and led display
> I wonder if it is possible to connect a second 8 segment led display
to
> bs2 without using all pins or the led driver circuit.
Sure, you only need to use one more pin to select which LED display
you're
talking to. This pin will enable one and disable the other LED display.
This
"trick" is call multiplexing. Two pins would allow you to select four
LED's;
three pins, eight, etc. Note that the more LED's you're multiplexing the
less time that any one LED display will be illuminated. You can
compensate
for this by increasing the available current thru an LED for the period
that
it's enabled. Usually this is done by increasing the supply voltage to
the
LED but you may be able to just decrease (or eliminate) the current
limiting
resistors for each LED display.
For an example of an 8-digit LED display see:
<http://www.maxim-ic.com/images/DI217Fig01.gif>
Here's a PIC circuit that drives four LED displays:
<http://picbasic.com/resources/articles/ledart.htm>
Another: <http://www.doug.h.rice.btinternet.co.uk/countdown/>
Personally I'd consider the led driver circuit. These usually
automatically
adjust the current to get a consistent brightness regardless of the
number
of segments illuminated.
--
Enjoy,
George Warner,
Schizophrenic Optimization Scientists
Apple Developer Technical Support (DTS)
To UNSUBSCRIBE, just send mail to:
basicstamps-unsubscribe@yahoogroups.com
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Yahoo! Groups Links
7-Segment Display that has its own internal driver which accepts "ABCD"
binary inputs. This with a single 74HC595 can control 2 Displays.
>A cheap 7-segment driver is a 74HC595 shift register. With just three
>Stamp pins you get eight outputs, and they can be daisy-chained if you
>want to add more displays.
>
>-- Jon Williams
>-- Applications Engineer, Parallax
>-- Dallas Office
>
>
>
Original Message
>From: Robert Bohlin [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=fej1fRHoG5V2JINapzampj-uWFVZ_rBuLwiU0apSikuc8y5N6gtzZe7tqLpHaQ3DWeNou3ieFRNolq-ljn3Etzg]robert.bohlin@b...[/url
>Sent: Wednesday, April 14, 2004 10:06 AM
>To: basicstamps@yahoogroups.com
>Subject: [noparse][[/noparse]basicstamps] BS2 and led display
>
>
>
>Hi!
>
>I wonder if it is possible to connect a second 8 segment leddisplay to
>bs2 without using all pins or the led driver circuit.
>
>Regards
>Robert
>
Beau Schwabe Mask Designer National Semiconductor Corporation
500 Pinnacle Court, Suite 525
Home: polygon_man@h... Mail Stop GA1
Work: bschwabe@a... Norcross, GA 30071
Yes for everything except the common (cathode or anode). This line is
switched separately to determine which display is enabled.
> I am a little confused about the wiring, although I understand the
> concept. I had students last semester experimenting with three to four 8
> segments on a BOE and the wiring was a mess as well as the project. I
> think it can be done though but I'm not sure. Could someone please
> expand on this topic?
Basically all the segments are connected in parallel between all the
displays but the common return lead for each display is switched separately
to only enable the one display that you're illuminating. This is done fast
enough that it appears that all displays are illuminated.
Yeah, it's spaghetti wiring unless you use a pre-wired multi-digit display
or one of the commercial circuit boards that do this for you.
A few more references: <http://www.phanderson.com/basicx/max7219.html>
<http://www.barcodemall.com/a1barcode/b14m04nr.html>
Here's a nice pre-assembled 4-digit LED display:
<http://handyboard.com/cricket/bus/4digit.shtml>
You can talk to it via two BS2 pins.
--
Enjoy,
George Warner,
Schizophrenic Optimization Scientists
Apple Developer Technical Support (DTS)