21 Oct
2005
21 Oct
'05
3:42 p.m.
I believe that all these LEDs are on ISA or EISA cards, circa 1987.
Let me be more specific now that I have gone to radio shack.
In 5mm red LEDs they have
12volt, 2.6v, 1.8v
Ignore the 12V one (and a 5V one if they listed that). Those have
built-in resistors or current source ICs and are not what you want at
all. Rememebr an LED is a semiconductor diode and this had a V-I
characteristing with a very steep slope (almost no change in voltage over
a wide range of currents), so you can't connect a bare LED to a voltage
supply. You would normally put a resistor in series with it.
Msot common red LEDs have a Vf (forward voltage) of 1.8V. Higher voltage
tend to be the modern low-current ones that you don't want. I'd get the
1.8V one and see what happens.
Except for very speicalised aplications I've never really worried about
the characteristics of the LEDs I am using. Just get a generic red LED
and pick a reisstor to pass between 10 and 20 mA through it.
-tony