|Making LED arrays from avail single digit models|
Message #24 Posted by glynn on 23 Mar 2003, 3:27 a.m.,
in response to message #19 by Vieira, Luiz C. (Brazil)
I proposed this long ago, but maybe time has come to suggest it again:
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"Another project that might be worthwhile in that vein is the matter of the "Classic" displays. They rely on an obsolete and hard-to-find five-digit seven-segment LED. Matched brightness on the three sets of five-digit displays are tough. BUT... A project to make a "drop-in" replacement for the display... a circuit-card with fifteen matched LED digits, is possible, if enough people want to do this. Single LED digits are easy to source, in many sizes. Design could probably proceed NOW."
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(from Archive 3, Aug 24 2000 "A modest proposal", one of many ideas tossed off in a rather long essay)
Basically, there ARE things out there to be done, either as a group, or by some entrepreneur-type who wants to supply to a market that is waiting.
The HP LEDs were actually rather small-charactered, but such was the state of the art back then; they made up for the tiny segments by encasing them behind clear epoxy lenses (one over each seven-segment character; this lent them a nice look head-on, and I believe made viewing them at an angle a bit easier, too-- but experimentation could tell you if an "unlensed" LED, maybe set a bit more forward in the case, would lead to increased readability. Character size itself might be a bit tweakable, too... all of that being behind the red bezel, you'd probably have to have two Classics side by side to tell the display was not an "original".
As Classics become more and more a collectible than a commodity, perhaps being as faithful to the original as possible is necessary. In which case, a molded clear styrene strip of "bubbles" might be worth attaching to small-segment arrays, for that authentic "HP" look. Cost of casting the bubble strips from Lucite would be nearly negligible, a "garage" operation. A rubber mold, a mild vacuum chamber to keep air pockets down, and resin two-part that you can acquire at most hobby chains. Even omit the vacuum if you don't mind a few spoilt strips due to air-resin mixing.
In short, Luiz, a bit of parts research would LIKELY get you closer to building "stick"s for yourself and others out of single character elements, and it seems to me that a run of fifty or so would prolly meet with an audience in Here.
Fifty assemblies would be large enough that you would be able to sort the elements out of those 750 singles sent you by a place like DigiKey by comparative brightness, so that all 15 in each calc's display would be pretty darn close to each other. If you do less than this, you need to have a supplier willing to sell you pieces sorted by codes from the production run. HP used to have letter codes characterizing brightness, and some LED manufacturers sort them out this way per tray.
(By the way--- regarding OLEDs--- they are a REAL technology now, not the vaporware they were when I was writing about us building our own design calculator two and a half years ago. At this moment, few facilities pump out OLED displays yet, and the concentration has been on dot-matrix arrays for PDAs etc., but that will likely change and some off-the-shelf small alphanumeric stuff is likely to appear in the next two years or so. Uniax (sold to Dupont Displays, look these guys up) was a developer of the "flexible" tech mentioned earlier in this thread, and the key there was that OLED could be PRINTED or silk-screened as part of a mylar sandwich, and thus it was very thin, dissipated its low but "age-producing" heat very well, and could be tooled up into unique designs incredibly cheaply; it was just printing, after all. I am a firm believer in OLED, and feel its color can be fairly well "tuned" to provide good readability even in bright light (not limited to reds, OLEDs make nifty greens and others too). My own preference is an amber-yellow on flat black, accomplished by shining the element through a fine mesh screen of black polyester. The contrast is incredible, and easy on eyes as well. If I ever DO design my own calc....)
Well, best of luck to all!