30 Sep
2008
30 Sep
'08
10:02 a.m.
On Tuesday 30 September 2008 08:54, Ethan Dicks wrote:
(Snip)
I can't look it up to verify at the moment (no satellite) in case I have
some digits swapped, but the part I'm thinking of was used in the RCA
MicroTutor II (the later 1802-based one, not the earlier 1801-based one),
a hand-held 1802 device that generates a lot of discussion on the cosmacelf
Yahoo Group, and the Quest SuperElf, among other places. The part is,
IIRC, a Fairchild part that does the same sort of decoding and segment
driving as a 7447. I couldn't describe any differences off the top of my
head though (except a different pinout).
There seems to be a fair amount of 9000-numbered stuff and other early TTL
that I haven't managed to accumulate much data on yet...
(Snip)
Thank you for mentioning this... I just read over an ancient TI datasheet
for the 7446-7449 family of decoder/drivers and there it is. I hadn't
really stared at that end of the decoded pattern to see that "F" renders
as blank. That could end up being quite handy.
The rest of the decoding is still rather weird, though. :-)
(Snip)
They're in my big genereic number chart, the last two entries just before the
z80 stuff:
http://www.classiccmp.org/rtellason/by-generic-number.html
I remember some of that, though it's been a rather long while since I looked
at any of those specs.
Yup.
(Snip)
Sounds a little familiar...
I got mine in the late 1970s in a $2 multi-pack at Radio Shack. I don't
have as many as I used to due to youthful exhuberance and destructive
testing (hint: they can't take a 9V supply without a resistor ;-)
No surprise there. :-)
The 7441 sounds right. I think someone rebadged a bunch of 7441s as 74141s
(or something similar), but they aren't particularly cheap. I think I have
one 7441 in a drawer.
I had one assembly that I'd picked up somewhere, a bunch of tubes in sockets
with a bit of perfboard underneath each having a 7441 on it, and that went
to the same guy that took the 1802-based system and the pdp8, he had a thing
for nixies as I recall.
Or on the board containing the display, often underneath it, at least in the
case of the VFDs. And those are very machine-specific too.
This was a VFD type of device he was talking about, I think. I'll have to
play with one at some point, and see what I can manage to get going with it.
A brief search a while back didn't yield much information, they don't seem
to be generic devices at all but mostly manufactured for the specific
equipment they're going into and sold in large quantities. Perhaps if I can
find the time to dig out some VCR service manuals and peruse that portion of
the circuitry I can get more of a grip on them.
--
Member of the toughest, meanest, deadliest, most unrelenting -- and
ablest -- form of life in this section of space, a critter that can
be killed but can't be tamed. --Robert A. Heinlein, "The Puppet Masters"
-
Information is more dangerous than cannon to a society ruled by lies. --James
M Dakin
I have one or two of a few different types, but no
loose 9368s (only
installed in boards already).
I'm not familiar with that one, offhand (and don't have it in my big
generic numbers chart). (the 7447 has incomplete decoding internally, so will
light various odd
segments if you don't stick to 0-9).
With blank for F IIRC, and I always wondered why they did it that way. I seem to
recall Radio Shack selling a couple of chips for that purpose,
75491 and 75492.
I'm unfamiliar with those. I should look them up. The former
had two sets of outputs but fairly limited drive capabilities,
while the latter was open-collector but could drive a good bit more if
I'm remembering right.
The 7446-7449 family has a similar spread of features. The 7448, IIRC,
can only sink 6mA and is designed to be externally buffered. They
didn't seem to be too friendly to common-anode displays, which is
what I was wanting to use at the time.
Ah... that is one of the reasons why TI made a spread of parts with
different drive capacities and other features. I seem to
recall Osborne using one of those, might've been the 6821,
and I don't think it took too much in the way of glue logic to make it
work on the z80 bus.
Nor the 6502 or pretty much any 8-bitter. The only thing that gets
sticky is when you have to fiddle between /WR + /RD lines vs a single
/WR-RD line ("motorola" vs "intel" bus standard as frequently
described
in docs on textual LCDs and VFDs). .... I did take a pair of raised-segment LEDs...
I saw the picture of those but don't recall ever actually seeing those
devices. Oh, yeah. So are small textual and graphical LCD and
VFD displays, but
there's a real appeal, to me at least, of the soft glow of red LEDs.
Not quite as cool as Nixies, but those evoke memories of a different
era.
Yep. I wouldn't mind getting some nixies to play with too, but those
are getting way too complicated too. And are the driver chips for them
available at all any more? What was it, the 7441? I have a few
LCDs I've been meaning to play with, and some VFDs out of
scrapped VCRs, most of which are too application-specific for me to want
to do anything much with them but one or two of the more
recently-acquired ones might be nice to do something with.
Many of those appliance displays are unformatted - the controller/driver
is embedded on the main board of the device. The ones I've played with have an HD44780 or some
graphical controller
(depending on the display type), and that takes care of strobing, driving
voltages, fonts, etc. You just worry about register-level formatting of
what you want to put on the display.
Yep, I need to figure out some uP that I want to play with those with. Or
maybe rig something with a parallel cable...
I don't have any experience driving
"naked" VFDs, but I have a few
panels and wouldn't mind taking a stab at it someday.
Nor do I.
Tony
mentioned some trick in the past week or two for a similar type of
device, though I think that was only a single indicator, as far as
making it work, and I was wondering how that might apply to a whole
display...
Much in the same way as things that kicked off this thread to begin
with - you have to have some part (dedicated or a custom-programmed MCU
for example) that strobes through the various display elements
(pixels/segments) and that you can address externally to end up with the
desired bits lit and unlit. I have a few naked LCDs that I'd love to play
with, but with all the formatted LCDs that are out there, I've never gotten
into driver specifics.