486 case LED display jumpers

[Philip Pemberton]

Teo Zenios wrote:
> Anybody happen to have the jumper diagram to set a LED 2 digit case speed setting? The PCB has ST-8A on it if that helps.

There's a reverse-engineered partial circuit on VOGONS:
http://vogons.zetafleet.com/viewtopic.php?t=10780&sid=f80bc89c785100a9d5bfa236f7e45b31

If you could put a photo of the PCB on one of those photo-sharing sites (say, 
Photobucket?) and post the URL, I might have the paperwork kicking around in 
one of my folders. "TH99" (Total Hardware, 1999 edition) might also be worth a 
look, copies of that are kicking around on Google.

Usually the jumpers are laid out in a tesselated "T" pattern, a bit like this:

1 2 3
   4

Valid jumper positions are 1-2, 2-3, 2-4 or no jumper. If memory serves, 1-2 
is "on with TURBO on", 2-3 is "on with TURBO off", 2-4 is "on all the time", 
no jumper is, well, segment not lit. Which segment is tied to which jumper 
cluster depends on the specific display in use.

Of course, you get boards designed by folks who thought they were being 
clever, which end up with a layout like:

1 a 3
b 4 c
1 d 3

(or something like that, I've probably got it at least a little wrong)

Letters = segments; 1,3,4 = supplies.

You could probably reverse-engineer one with a multimeter in about 25 minutes. 
Remove all the jumpers, Set TURBO off, find all the lines that are high, 
repeat with TURBO on. From that you'll be able to figure out which pins are 
always-high, and which depend on the state of the TURBO input. Anything that 
stays low is a segment. If dealing with a common-anode display, reverse "high" 
and "low".

-- 
Phil.
classiccmp at philpem.me.uk
http://www.philpem.me.uk/