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74C925 alternative?

J

jimi

Jan 1, 1970
0
Does anyone know of an alternative for the 74C925 chip for driving 4x7
segment LED's. The chip seems to be obsolete. Thanks
 
R

Richard Seriani, Sr.

Jan 1, 1970
0
jimi said:
Does anyone know of an alternative for the 74C925 chip for driving 4x7
segment LED's. The chip seems to be obsolete. Thanks
I've never dealt with this company, but your 74C925 does show up in a seach.

http://www.hobid.com/itk/12.html

Good luck.
Richard
 
jimi said:
Does anyone know of an alternative for the 74C925 chip for driving 4x7
segment LED's. The chip seems to be obsolete. Thanks

Use a programmable logic device or an Arizona Microsystems PIC
processor - I'm not far enough into either option to identify a part
which comes in the right 16-pin 0.3" dual-in-line package (and it
might be difficult to find a programmable logic device with enough
buried flip-flops to do the job in an essentially obsolescent package)
but somebody will know.
 
D

Don Lancaster

Jan 1, 1970
0
Use a programmable logic device or an Arizona Microsystems PIC
processor - I'm not far enough into either option to identify a part
which comes in the right 16-pin 0.3" dual-in-line package (and it
might be difficult to find a programmable logic device with enough
buried flip-flops to do the job in an essentially obsolescent package)
but somebody will know.
Maxim has some super duper new LED drivers.

--
Many thanks,

Don Lancaster voice phone: (928)428-4073
Synergetics 3860 West First Street Box 809 Thatcher, AZ 85552
rss: http://www.tinaja.com/whtnu.xml email: [email protected]

Please visit my GURU's LAIR web site at http://www.tinaja.com
 
J

jimi

Jan 1, 1970
0
Thanks for the replies, however, I asked the question so I could avoid
using a microcontroller.
 
D

Donald

Jan 1, 1970
0
jimi said:
Thanks for the replies, however, I asked the question so I could avoid
using a microcontroller.
Thinking out loud,

With simple CMOS technology going away, wouldn't it be wise to replace
it with something you can get in a few years.

Once you get C code running, going to a smaller uC would be easier the
second time.

What ever chip you find today, will be gone next year.

good luck

donald
 
So you wnat the OP to replace a 16-pin DIP with a 28-pin DIP that
Intersil has marked "inactive".
A small microcontroller, however, would be my first choice.

I'd prefer a programmable logic part - the 4-digit counter is not
synchronous with the multiplexing logic for the display. Back in 1972 I
dealt with this problem by freezing the multipexing clock until any
incoming count had rippled through the (asynchronous) counters, which
took up to 4usec. This wasn't an elegant solution. With a
microcontroller, I guess you'd rely on the interrupt system to capture
clock increments that occured at the wrong instant, and you'd keep your
interrupt handler short and quick to keep the maximum count rate
respectable.

Programmable logic offers true parallel processing, which can be a lot
tidier.
 
A

Arlet

Jan 1, 1970
0
I'd prefer a programmable logic part - the 4-digit counter is not
synchronous with the multiplexing logic for the display. Back in 1972 I
dealt with this problem by freezing the multipexing clock until any
incoming count had rippled through the (asynchronous) counters, which
took up to 4usec. This wasn't an elegant solution. With a
microcontroller, I guess you'd rely on the interrupt system to capture
clock increments that occured at the wrong instant, and you'd keep your
interrupt handler short and quick to keep the maximum count rate
respectable.

Programmable logic offers true parallel processing, which can be a lot
tidier.

Many microcontrollers have built-in timers than be driven from external
clock. This isn't truly asynchronous, because the external clock is
typically sampled on the internal clock, but it still allows quite fast
operation. For speeds <= 1MHz, a cheap microcontroller will work fine.
 
J

John Fields

Jan 1, 1970
0
So you wnat the OP to replace a 16-pin DIP with a 28-pin DIP that
Intersil has marked "inactive".

---
1. I don't "want" the OP to do anything; I presented him with an
option to the 925 as he requested. Whether he chooses to use
it or not is entirely up to him.

2. Whether Intersil has marked it inactive or not, the part is
currently in production and is available. Digi-Key, for
example, has 807 pieces in stock, Newark-in-One 236, and I
suppose if took the time to look further I could find even
more sources.
---

I'd prefer a programmable logic part - the 4-digit counter is not
synchronous with the multiplexing logic for the display. Back in 1972 I
dealt with this problem by freezing the multipexing clock until any
incoming count had rippled through the (asynchronous) counters, which
took up to 4usec. This wasn't an elegant solution.
 
Yes just the filament supply for all those 12AT7's must have been
unwieldy, to say the least.
---

I don't know what you were doing in 1972 - the fact that you haven't
yet got past 555's does suggest that you aren't an early adopter - but
my toy used TTL logic and Beckman 7-segment fluorescent displays, with
a few transistors to handle the voltage swings.

And not a filament in sight (nor any hidden filaments either)

Looked quite neat.
 
J

John Fields

Jan 1, 1970
0
I don't know what you were doing in 1972 - the fact that you haven't
yet got past 555's does suggest that you aren't an early adopter

---
I'd say that statement more nearly categorizes your position than
mine since I adopted them way back when they first came out. You,
on the other hand, have yet to use one (by your own admission) so
I'd say you're the one who's a little late getting on the bandwagon.
---

- but
my toy used TTL logic and Beckman 7-segment fluorescent displays, with
a few transistors to handle the voltage swings.

And not a filament in sight (nor any hidden filaments either)

---
Sorry, Charlie, but vacuum fluorescent displays _do_ have filaments.

Where do you think the electrons used to illuminate the phosphors
come from, otherwise?
---
 
S

Spehro Pefhany

Jan 1, 1970
0
---
I'd say that statement more nearly categorizes your position than
mine since I adopted them way back when they first came out. You,
on the other hand, have yet to use one (by your own admission) so
I'd say you're the one who's a little late getting on the bandwagon.
---



---
Sorry, Charlie, but vacuum fluorescent displays _do_ have filaments.

Where do you think the electrons used to illuminate the phosphors
come from, otherwise?

The Beckman displays were flat panel plasma discharge displays, sort
of like Nixies but segmented and with the segments all in one plane.
You used to seem them on gas pumps until fairly recently as well as
some industrial instruments (Simpson had a fairly successful series of
instruments that used them). National semi made a biplar driver chip
DS8880 or something like that.. ah, here it is:
http://www.sphere.bc.ca/test/nixies/ds7880.pdf


Best regards,
Spehro Pefhany
 
J

John Fields

Jan 1, 1970
0
On Sat, 02 Dec 2006 08:42:44 -0600, the renowned John Fields


The Beckman displays were flat panel plasma discharge displays, sort
of like Nixies but segmented and with the segments all in one plane.
You used to seem them on gas pumps until fairly recently as well as
some industrial instruments (Simpson had a fairly successful series of
instruments that used them). National semi made a biplar driver chip
DS8880 or something like that.. ah, here it is:
http://www.sphere.bc.ca/test/nixies/ds7880.pdf
 
John said:
---
I'd say that statement more nearly categorizes your position than
mine since I adopted them way back when they first came out. You,
on the other hand, have yet to use one (by your own admission) so
I'd say you're the one who's a little late getting on the bandwagon.
---



---
Sorry, Charlie, but vacuum fluorescent displays _do_ have filaments.

Where do you think the electrons used to illuminate the phosphors
come from, otherwise?
---
From positive ion bombardment of the negatve electrode - the "glow
discharge" discharge mechanism - in a low pressure of some noble gas
(probably neon, but I can't be sure) and certainly not fom a filament.
There was a small, steady "keep alive" corona discharge hdden behind an
opaque bit of the glass front, and the active segments lit up when you
hit them with something over 180V, whch would have been around the
Passchen minimum for avalanche discharge through neon. Without the
keep-alive discharge, fast multiplexing could be chancey - it was an
added extra feature in the second generation of the displays.

Agreed. The Beckman displays were nicer than most but the 180V seems to
have been unpopular.
 
J

jasen

Jan 1, 1970
0
Does anyone know of an alternative for the 74C925 chip for driving 4x7
segment LED's. The chip seems to be obsolete. Thanks

use a microcontroller?
 
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