LED displays (TIL305, TIL308, etc.)
Roy J. Tellason
rtellason at verizon.net
Tue Sep 30 12:02:49 CDT 2008
On Tuesday 30 September 2008 08:54, Ethan Dicks wrote:
> > > 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).
> 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...
> > > (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.
> 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. :-)
> > 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.
They're in my big genereic number chart, the last two entries just before the
> > 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.
I remember some of that, though it's been a rather long while since I looked
at any of those specs.
> > 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).
Sounds a little familiar...
> > > .... I did take a pair of raised-segment LEDs...
> > I saw the picture of those but don't recall ever actually seeing those
> > devices.
> 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. :-)
> > > 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?
> 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.
> > 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.
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.
> 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.
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.
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