I have been given a large number of LEDs soldered into a board. Since the
pins have been cut t the same length what is the best way of determining
their polarity when removed from the board?
For decades, I've always had a 9v battery lying around with about a 1K
resistor soldered to one terminal, and sometimes a piece of wire soldered
to the other. Since you know the polarity of the battery, when the LED
lights up when you connect it, you know which terminal of the LED is which.
If it doesn't light up, you reverse the LED. If it doesn't light up then,
the LED is a dud (or your battery has finally died.
This not only gives you polarity when it may not be clear, but if the flat
of the package isn't visible (like when you've installed it with one of
those LED holders) or whatever reasons, you can easily check before soldering.
I got into the habit of checking LEDs this way before soldering because when
I first started buying them, LEDs were relatively new and it was easy to
get some that were not particularly bright, or for that matter I think
some that were cheap because they had the terminals reversed.
Michael