Driving 16 7-Segment Displays

[[email protected]]

Hi,
I'm just completed a progject where it's necessary to drive 16
displays (7-segment). Because I didn't want to tie up the
microcontroller and have maximum brightness, I used Maxim's MAX7219.
This works perfectly but I need to have 2 of them as they only drive 8
digits each.

Problem is they are expensive devices. I wondered if there are other
similar devices or methods I could use without tying up the
microcontroller. (uPD78F0034)

Thanks,
Joe

PS. If I didn't use any display drivers. Would an 8Mhz micro be able
to get around all the displays (not diming too much) and monitor a 4x4
keypad input also???

 

[Tim Mitchell]

Hi,
I'm just completed a progject where it's necessary to drive 16
displays (7-segment). Because I didn't want to tie up the
microcontroller and have maximum brightness, I used Maxim's MAX7219.
This works perfectly but I need to have 2 of them as they only drive 8
digits each.

Problem is they are expensive devices. I wondered if there are other
similar devices or methods I could use without tying up the
microcontroller. (uPD78F0034)

Thanks,
Joe

PS. If I didn't use any display drivers. Would an 8Mhz micro be able
to get around all the displays (not diming too much) and monitor a 4x4
keypad input also???

I have used 74HC574 latches to drive 7-seg displays when multiplexing is
undesirable. They're cheap. 74HC595 serial to parallel latches also work
if you don't have many processor pins to drive it with.

 

[petrus bitbyter]

Hi,
I'm just completed a progject where it's necessary to drive 16
displays (7-segment). Because I didn't want to tie up the
microcontroller and have maximum brightness, I used Maxim's MAX7219.
This works perfectly but I need to have 2 of them as they only drive 8
digits each.

Problem is they are expensive devices. I wondered if there are other
similar devices or methods I could use without tying up the
microcontroller. (uPD78F0034)

Thanks,
Joe

PS. If I didn't use any display drivers. Would an 8Mhz micro be able
to get around all the displays (not diming too much) and monitor a 4x4
keypad input also???

As so often, it all depends...

You can use sixteen old CD4511 BCD to seven segment decoder/driver chips
along with eight CD4015 shift registers. It - again - depends on the
available input format of your data. This components are cheap, but you
need twentyfour pieces. Component count, pin count and board space also have
a cost tag.

A modern aproach is using programmable logic. Can't be difficult to find one
with plenty of I/O pins. You can even emulate two MAX7219 in it... as far as
the logic concerns. Output current may be a problem. Of course you need to
write the content (program) and you need a programming facility. Can become
more expensive then two MAX7219.

An 8MHz can be easily tied up to do the job. Available output current may
become a problem. So you have to use maybe twentythree transistors.
Brightness depends on the current so you can control this with the serial
resistor. (To some extent of course.) A 4x4 keyboard can be added easily.
Even then the micro will be waiting most of its time.

More details can't be given as I don't know the available input signals,
power supply, LED displays and their application data.

petrus bitbyter

 

[Joerg]

Hi Tim,

I have used 74HC574 latches to drive 7-seg displays when multiplexing
is undesirable. They're cheap. 74HC595 serial to parallel latches also
work if you don't have many processor pins to drive it with.

Or the 14094 but that would only work for low power apps, not for large
displays.

Regards, Joerg

 

[Rich Grise]

As so often, it all depends...

You can use sixteen old CD4511 BCD to seven segment decoder/driver chips
along with eight CD4015 shift registers. It - again - depends on the
available input format of your data. This components are cheap, but you
need twentyfour pieces. Component count, pin count and board space also
have a cost tag.

Heavens to Murgatroyd! What a potload of parts! You need 1X 74HC154 for
the 16 digits, and 1X octal buffer for the segments and decimal points.
Or you could use a BCC-7seg decoder and use only half of that port, but
lose the decimals.

Appropriate resistors all around, and you're good to go. Well, after
you write the driver. ;-)

Cheers!
Rich

 

[Stefan Heinzmann]

petrus bitbyter wrote:




Heavens to Murgatroyd! What a potload of parts! You need 1X 74HC154 for
the 16 digits, and 1X octal buffer for the segments and decimal points.
Or you could use a BCC-7seg decoder and use only half of that port, but
lose the decimals.

Appropriate resistors all around, and you're good to go. Well, after
you write the driver. ;-)

Add transistors to the outputs of the 74HC154 or the result will be
rather dim. ;-)

 

[petrus bitbyter]

Add transistors to the outputs of the 74HC154 or the result will be
rather dim. ;-)

Well guys,

The Maxim mentioned by the OP uses a three wire interface. Guess you'll have
to add some more electronics to make your design work. Shift registers for
instance. Keep also in mind that neither the octal buffer nor the 74HCT154
can handle the currents required to make a bright display. Nevertheless
it's another possibility but the three I mentioned. As so often, there are
more ways to skin a cat.

petrus bitbyter

 

[Pooh Bear]

Hi,
I'm just completed a progject where it's necessary to drive 16
displays (7-segment). Because I didn't want to tie up the
microcontroller and have maximum brightness, I used Maxim's MAX7219.
This works perfectly but I need to have 2 of them as they only drive 8
digits each.

Problem is they are expensive devices. I wondered if there are other
similar devices or methods I could use without tying up the
microcontroller. (uPD78F0034)

Multiplex the LED common anode or cathode connection using an 8 bit latch
and transistors ( for cheapness ) Ditto for the segments.

2 * 8 bit latches and 16 transistors. You can use the more expensive
integrated driver chips if you like.

Thanks,
Joe

PS. If I didn't use any display drivers. Would an 8Mhz micro be able
to get around all the displays (not diming too much) and monitor a 4x4
keypad input also???

Yes. I've driven a 16 character, 16 segement VFD from an 8051@12MHz and it
was a background task. It did *plenty* more including scanning a load of
keys too.


Graham

 

[Roger Gt]

message : [email protected] wrote:
:
: > Hi,
: > I'm just completed a project where it's necessary to drive
16
: > displays (7-segment). Because I didn't want to tie up the
: > microcontroller and have maximum brightness, I used Maxim's
MAX7219.
: > This works perfectly but I need to have 2 of them as they only
drive 8
: > digits each.
: >
: > Problem is they are expensive devices. I wondered if there are
other
: > similar devices or methods I could use without tying up the
: > microcontroller. (uPD78F0034)
:
: Multiplex the LED common anode or cathode connection using an 8
bit latch
: and transistors ( for cheapness ) Ditto for the segments.
:
: 2 * 8 bit latches and 16 transistors. You can use the more
expensive
: integrated driver chips if you like.
:
:
: >
: > Thanks,
: > Joe
: >
: > PS. If I didn't use any display drivers. Would an 8Mhz micro
be able
: > to get around all the displays (not dimming too much) and
monitor a 4x4
: > keypad input also???
:
: Yes. I've driven a 16 character, 16 segment VFD from an
8051@12MHz and it
: was a background task. It did *plenty* more including scanning a
load of
: keys too.
: Graham

The logic used to be available in a single chip from Intel I think
an I8253.
You only had to add the transistors to drive a 16 digit display.

 

[Spehro Pefhany]

The logic used to be available in a single chip from Intel I think
an I8253.

No, i8279. The 8253 was a timer peripheral.

You only had to add the transistors to drive a 16 digit display.

Best regards,
Spehro Pefhany

 

[Pooh Bear]

message : [email protected] wrote:
:
: Yes. I've driven a 16 character, 16 segment VFD from an
8051@12MHz and it
: was a background task. It did *plenty* more including scanning a
load of
: keys too.
: Graham

The logic used to be available in a single chip from Intel I think
an I8253.

I bet a single chip from Intel would be pricier than a few 74HC574s !

You only had to add the transistors to drive a 16 digit display.

To save space ! I used Rohm's 'digital transistors' that have an
integrated base resistor. Handy things. DTA114 IIRC.

Graham

hmmm - a quick google shows that On Semi do the DTAs now too

 

[Roger Gt]

message : Roger Gt wrote:
:
: > message : > : [email protected] wrote:
: > :
: > : Yes. I've driven a 16 character, 16 segment VFD from an
: > 8051@12MHz and it
: > : was a background task. It did *plenty* more including
scanning a
: > load of
: > : keys too.
: > : Graham
: >
: > The logic used to be available in a single chip from Intel I
think
: > an I8253.
:
: I bet a single chip from Intel would be pricier than a few
74HC574s !

They were about $3 but they are long gone. Had to program a FPGA
to support the product. It contained the memory, decode and
scaning.

: > You only had to add the transistors to drive a 16 digit
display.
:
: To save space ! I used Rohm's 'digital transistors' that have an
: integrated base resistor. Handy things. DTA114 IIRC.
:
: Graham
:
: hmmm - a quick google shows that On Semi do the DTAs now too
:

 

[Rich Grise]

To save space ! I used Rohm's 'digital transistors' that have an
integrated base resistor. Handy things. DTA114 IIRC.

Graham

hmmm - a quick google shows that On Semi do the DTAs now too

Is anybody still making the ULN2803?

Cheers!
Rich

 

[Tim Mitchell]

To save space ! I used Rohm's 'digital transistors' that have an
integrated base resistor. Handy things. DTA114 IIRC.

Graham

hmmm - a quick google shows that On Semi do the DTAs now too

Is anybody still making the ULN2803?
[/QUOTE]
Yeah, loads of people.

 

[Wouter van Ooijen]

Is anybody still making the ULN2803?

The ones I sell state "Thosiba".


Wouter van Ooijen

-- ------------------------------------
http://www.voti.nl
PICmicro chips, programmers, consulting

 

[Anders F]

Hi,
I'm just completed a progject where it's necessary to drive 16
displays (7-segment). Because I didn't want to tie up the
microcontroller and have maximum brightness, I used Maxim's MAX7219.
This works perfectly but I need to have 2 of them as they only drive 8
digits each.

There are lots of alternatives! Others mentioned static latches or drivers
(great for low EMI and optimal brightness)...

Problem is they are expensive devices. I wondered if there are other
similar devices or methods I could use without tying up the
microcontroller. (uPD78F0034)

Thanks,
Joe

PS. If I didn't use any display drivers. Would an 8Mhz micro be able
to get around all the displays (not diming too much) and monitor a 4x4
keypad input also???

No problem! I'm doing 4 on a ~1MHz (a cheap MSP430)- also doing translation
and software based UART at 9600baud. A few fets for the common anode drivers
and uC outputs/resistors for the segments... For a
not-so-price-sensitive-application one might consider some constant current
drivers...

Regarding the multiplex you have to consider the needed brightness to
determine the groups. You can increase the current for the low duty cycles
(ie. 1/16) - but then you need to make sure the system will never stop with
a driver active... Otherwise a 1/4 is probably what you can do with
resonably brightness on a uC output - maybe 1/8 with low current diplays.

Regards,
Anders

 

[Spehro Pefhany]

The ones I sell state "Thosiba".

Must be knock-offs.

Best regards,
Spehro Pefhany

 

[Wouter van Ooijen]

Must be knock-offs.

dunno what you mean by 'knock-offs', they are certainly not the first
manufacturer of this part, but according to their website is is normal
production.


Wouter van Ooijen

-- ------------------------------------
http://www.voti.nl
PICmicro chips, programmers, consulting

 

[Spehro Pefhany]

dunno what you mean by 'knock-offs', they are certainly not the first
manufacturer of this part, but according to their website is is normal
production.

Ha, well, I have also seen not-so-original stuff marked "Tobishi" (in
an identical script font to the original), but the real manufacturer
of this stuff is likely "Toshiba" (from "Tokyo Shibaura Denki").

Best regards,
Spehro Pefhany

 

[Wouter van Ooijen]

Ha, well, I have also seen not-so-original stuff marked "Tobishi" (in

an identical script font to the original), but the real manufacturer
of this stuff is likely "Toshiba" (from "Tokyo Shibaura Denki").

Aha, I meant to say that I inserted an extra h. Indeed, the chip reads
Toshiba. I get them from a big Dutch distributor, if it were
counterfeit most Dutch electronics shops would be selling crapt. And
IIRC you would be using it too


Wouter van Ooijen

-- ------------------------------------
http://www.voti.nl
PICmicro chips, programmers, consulting