30 May
2015
30 May
'15
3 p.m.
On 2015-May-30, at 9:19 AM, Jules Richardson wrote:
On 05/29/2015 08:53 PM, Brent Hilpert wrote:
Yes, I've no idea how many of these ones are still working - although given that
they're intact on PCBs, my guess is that they're the result of board-swaps and so
one or two digits/modules may be out (or there are other board faults) but the rest are
still operational.
In total, not counting ones which physical damage or obviously-failed segments, I think I
have around 20 each of dual and triple-digit ones, plus a handful of quads, which is
enough to do something with while having a spares stock. Hopefully the pair of PSUs that I
rescued are OK, as they've got handy 6V->180V DC convertor modules on them.
If you look closely at the displays, esp. at an angle to the glass, you can see the anode
coating on the inside surface of the glass. If you see a red/brownish non-uniform
discoloration in that coating, or discoloration around the ends of the segment bars, or
some black spots on the segment bars, that can be an indication of 'burning' or
'wear'. Not sure how bad it has to get before it's a failure/problem, or how
long it might last once that begins to appear.
There should be nice high-voltage drivers on those boards too.
. . .
I'm
almost certain that they're from old gas pumps - maybe the
displays are just more readable in bright sunlight than LED? (there's
a sticker on one of the PSU boards with a 'shipping date' in 1999)
Funny, I was about to mention that use. I remember them in use on gas
pumps up to somewhere around the late-80s or early-90s. One of my bike
routes takes me on a dike behind an industrial area. Sometime around the
mid-90s I remember there being a yard filled with scrapped pumps, a lot
of them missing the display/keyboard cover, so all the displays mounted
on the big controller boards could be seen. I wanted to rescue some of
them but never got around to pursuing it. I was kind of dissuaded by the
thought they had mostly seen a long and continuous service life and may
now(then) be of questionable reliability. At the start of the decide, certainly - but by 1980 I
would have thought that the cost had come down significantly, and LEDs surely had better
longevity than panaplex-type devices, so I don't know what the reasoning for using
them would have been.
Thinking about it though, I'm not sure that I've ever seen a gas (petrol) pump
with LED displays, although I don't know why they wouldn't exist. Mechanical
displays seemed to be the norm back in the day, to be replaced by LCD displays in the
nineties and 2000's.
No, I never saw gas pumps with LED displays. As I recall, gas pumps around here went from
mechanical to Beckman GD displays sometime in the mid-70s, then transitioned to LCD in the
late-80s/early-90s. So pumps in Britain never saw the gas-discharge display generation?
I think the display quality in the daylight may have been an issue, as you were raising
earlier. Larger-size 7-seg LED displays in the early days weren't particularly good in
high ambient light. Contrast was poor and segment illumination could be non-uniform as
they piped the light out from the LED die(s) into the clear plastic bar forming a
segment.
Theorising here, but the ability to use polarising filters on the GD displays may have
been a comparitive benefit. Not sure you could use a polarising filter on LED displays as
the emitted light may be non-uniformly polarised from differing orientations of the LED
dies, so it wouldn't make it through a polarising filter uniformly.
Speaking of old display technology, as someone who has been collecting NIXIE and
other-display-type equipment for many years, the NIXIE clock craze of the past few years
has been a bit of a surprise. And now that crowd has discovered the other old display
types such as the 7-segment incandescent Numitron & minitron displays, which are quite
rare. If you want a display technology that was obsolete almost from the day it was
introduced that would be it.
If I ever get around to building a NIXIE clock, I was going to try putting a motion
detector in it to turn the display on/off for the sake of longevity of the displays.