BCD to hexadecimal 7 segment LED driver

[Eric]

Once upon a time in the 70's Motorola came out with a
BCD to hexadecimal 7 segment LED driver in the MC144xx series,

Instead of displaying rubbish characters between binary input 1010 to 1111
it displayed hexadecimal A to F

But wait that is not all, it did not need 7 limit resistors, that so many
(all) other "BCD to 7 segment LED drivers" need,

Every time I see a circuit that uses "BCD to 7 segment LED driver" in it
there are also the other 7 resistor there too,

I thought it was great I used a few, I wonder why they never took off

 

[Spehro Pefhany]

On Fri, 6 May 2005 04:53:03 +1200, the renowned "Eric"
<haha@clear.i.never.see.junk.mail.com> wrote:

Once upon a time in the 70's Motorola came out with a
BCD to hexadecimal 7 segment LED driver in the MC144xx series,

Instead of displaying rubbish characters between binary input 1010 to 1111
it displayed hexadecimal A to F

But wait that is not all, it did not need 7 limit resistors, that so many
(all) other "BCD to 7 segment LED drivers" need,

Every time I see a circuit that uses "BCD to 7 segment LED driver" in it
there are also the other 7 resistor there too,

I thought it was great I used a few, I wonder why they never took off

Hmm. Are you sure you're not conflating the DM9368 driver chip from
Fairchild vs. the Motorola MC14511 (which is a CMOS chip with NPN
emitter-follower bipolar drivers, and does require current limiting
resistors)? That's the only one that I can recall that decoded hex,
and it also had the constant current outputs of which you speak.

The reasons probably had to do with second sources, price and
availability. That's why we never used them. OTOH, there's a 4511 in
each of our mass-produced CO detectors we have at home.


Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
speff@interlog.com Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com

 

[Mark Zenier]

In article <427a4f8f$1@clear.net.nz>,
Eric <haha@clear.i.never.see.junk.mail.com> wrote:

Once upon a time in the 70's Motorola came out with a
BCD to hexadecimal 7 segment LED driver in the MC144xx series,

Instead of displaying rubbish characters between binary input 1010 to 1111
it displayed hexadecimal A to F

But wait that is not all, it did not need 7 limit resistors, that so many
(all) other "BCD to 7 segment LED drivers" need,

Every time I see a circuit that uses "BCD to 7 segment LED driver" in it
there are also the other 7 resistor there too,

I thought it was great I used a few, I wonder why they never took off

They were obselete not long after their introduction. After
the late '70s, just about everything with a display used a
microprocessor.

Jameco probaly still has them. At only two or three times
the price of a PIC.

Mark Zenier mzenier@eskimo.com Washington State resident

 

[Tim Shoppa]

LED driver in the MC144xx series

MC14495 is I think what you're writing about.

The Fairchild DM9368 is still out there and does hex too.

TI and I think HP also had LED displays with on-display hex
decoders/drivers.

it did not need 7 limit resistors

There are lots of LED driver chips from TI/Allegro/Micrel which have
constant current drivers on the chip. They do not do hexadecimal
decoding, their input interface is simply a bit-per-segment shift
register, this works great with modern microcontrollers, you simply
have a little lookup table in your program to produce the desired
display.

A bit older (but I think still available) is the MM5450 for LED
driving.

The Motorola MC14499 put a four-digit seven segment multiplexed driver
into a single 16-bit DIP, with a serial interface for data in. But it
didn't do hex.

Tim.