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choosing correct resistor for LED

stormin norman

Dec 1, 2011
Dec 1, 2011
I followed the tutorial link above and read thru what should be simple understandable language...but I'm stuck on de-ciphering the basics. I picked up a Radio SHack #276-0036 5mm blinking red LED. Package lists absolute ratings as supply voltage 5VDC forward current 80 mA reverse voltage 0.4VDC. Assuming I use a 9v batt what do I need for resistor? Or if I use one of my 'old' Sure Fire 3v batt. Then what resistor do I go with. This is 'simple' knowledge I just need to learn it and retain it. Thanks folks!
OK, so I also found this link....
which made this task somewhat easier.
Source voltage
diode forward voltage
diode forward current (mA)
When I plug the numbers from the back of the pack I am entering 5 for the diode forward voltage and 80 in the forward current. Source voltage I entered 9.
I get a red flag
The wizard thinks your forward voltage spec is suspiciously high, but will proceed with the calculations. Please double-check your specs.

but it gave me info back.
Am I safe in going with this?
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