Re: Thanks to all - well most...

On Tue, 01 Apr 2008 20:41:19 +1300, Terry Given <my_name@xxxxxxxx>
wrote:



[1] surely you're familiar with the term "dim."


Nice!


I have taken measurements that are almost identical. The first LED video
screen I worked on had a circuit that measured the LED forward voltage.
The way it was configured pumped 1uA into the LEDs, and was (barely)
visible. It turned out to be easier for me to measure sub-microamp
"leakage" currents with a vacuum cleaner. We had bugger all test gear
(almost everything I used I was renting to the company), and the "nook &
cranny cleaning" pipe from the end of the vacuum cleaner was thick black
plastic that tapered down to a narrow slot; black tape made it narrower
still. By placing it over a led with my eye firmly over the other end, I
could see well below 1uA.

the problem turned out to be easy to fix, and was inherent on the design
of the voltage sensing circuit (not mine), which I duly modified. 3
years later I left, and the guy who designed the original circuit
changed it back the next PCB revision (he never did like me). Funnily
enough, they had a huge problem with contrast (black isnt very black
when all the LEDs are glowing faintly), and had to do another PCB
respin. He didnt use my exact fix, rather its dual, which ended up being
more expensive. pants-wettingly funny. That firm made all their
technical staff redundant this year (including him), and no longer build
anything.


Let me guess - they went onto fabless dsp-intensive AV controllers....
with a new crop of wonder boys, known to the new venture capitalists.

RL
.

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