Re: Help needed ppwith LED's from somone with a very simplistic knowledge of electron
Hi,
The header current is limited to 25 mA at 3.3V.
Keep in mind, however, that it was designed to drive an LED with a forward voltage drop which is typically around 2V, therefore pulling approximately 10 mA.
This sounds as if there is an internal 130 Ohms resistor:
* if you short the output, then there is the whole 3.3V across the resustor: I = 3.3V / 130 Ohms = about 25mA
* if you connct the LED with it's 2.0V, then there remains 3.3V - 2.0V = 1.3V across the resistor. 1.3V / 130 Ohms = 10mA.
--> you don't need an extra current limiting resistor, just the bare LED.
There is about no risk to fry the LED output. But use ESD protection like an ESD wrist band.
I'm sure this is true for each single LED, not the common LED current.
Use LEDs with 2.0V: red, green, yellow, amber. (Vf: 1.6...2.3V, usually they have around 10..30mA typical forward current)
(but not: blue, white)
In doubt use standard LEDs, like 3mm or 5mm diameter, they may be in a case for easier mounting.
Mind that you need to take care about LED direction.
Usually the longer LED connection is anode, connect it to "+"
The shorter wire is cathode, "-".
Klaus