Hello question about led's

Badger

Hello

how much resistance does a single led produce. How many led's can you hook up in series on a pin to add up to a resister and a led. .

if someone would be so kind . I have a boe with a bs2px chip. what is the total power out put can it handle what is the safe zone area.

also i have a hwb i would like to know the same info on it.

i am sorry all but due to some problems tonight i am unable to read much on the computer at all. it is not the computer but my eyes. I have mentioned several times about my meds and how unhealthy i am. not going to post that again tonight so but i will say it is related . so if you all would be so kind to help me with this info i would appreciate it.

I have a topic in robotics something like this but not meant to be the same. i am looking for some thing very specific here.

if i have to use a resister what would be the lowest rating i can go if i could daisy chain say 5 leds together.
if i have to use a resister to protect my board could a diode be used in stead .

i am starting to put some stuff together but i am in the ocean and just learning to swim . I just hope i dont sink

thanks in advance as i humbly ask

Badger

Beau Schwabe

Badger,

LED's are not really resistive devices, they are current devices. They each have what's called a band-gap voltage or (Forward voltage) that is different from LED to LED depending on the color of the LED with slight variations from LED to LED of the same color.

Usually the manufacturer will provide this information as far as the current and forward voltage.

For a typical RED LED, the forward voltage is about 1.7V and 10mA of current is usually sufficient. Some more efficient LED's can go down as low as 2mA of current or less.



The formula for determining the correct current limiting resistance is as follows...

Current Limiting Resistor = The forward LED voltage subtracted from the voltage source and divided by the current requirement of the LED

Or

R = (Vsource-Vled)/Iled

Suppose your voltage supply was 12V and you wanted to power a RED led at 10mA.

R = (12V-1.7V)/.010
R = 10.3/.010
R = 1030 or a 1K resistor

Suppose you had five RED LED's you wanted to power in series at 10mA...

R = (12V-(1.7Vx5))/.010
R = (12V-8.5V)/.010
R = 3.5V/.010
R = 350 or a 330 Ohm resistor

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Beau Schwabe

IC Layout Engineer
Parallax, Inc.

LoopyByteloose

Badger,
I took me many years to accept the fact that some devices are NOT resistive in the normal sense.
Semiconductors are the primary example and it is mostly because of many ways they can be constructed. LEDs happen to be just another semiconductor.

The real problem is that too much current usually rather than too much voltage tends to be the first destructive factor in semiconductors. One sees this in circuits that have a 120V that use simply a resistor and an LED as a pilot light. It seems quite odd at first, but since the LED is properly 'current limited' it happily performs.

If you really have trouble with this take a look at the following site for a NEETs module that explains solid state devices. It helped me quite a bit.

http://www.rarmy.com/coleman/neets/

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