Justin DavisI got the standoffs soldered and two of the LEDs. I wanted to check the brightness on the LEDs before soldering all of the resistors. I decided 250 Ohms was still too much current, so I started with a 1kOhm resistors. I put two on the board and tried them out. And they were still very bright.
There's no big diffuser on smalll LEDs like this, so all the brightness is very concentrated. I ended up writing a custom program with analogWrite and jumpered with a wire over to the LEDs to see what would be an acceptable brightness. I think if I had about 1/10th of the current it would be fine. So that means 10kOhm resistors. I'll remove the 1k and replace with 10k.
I also found that with this many headers it's very tough to get the shield on and off easily. Perhaps with more repeated on/off cycles it will get easier.
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assuming 5V operations, the datasheet says 1.95V drop, so that is 3.05V that the current limiting resistor needs to handle. 3.05/1000 = 0.00305A or 3mA. now with this being a super bright LED with 80mcd, operating at that current seems possible to be still pretty bright, but using the same math with a 10k resistor makes that 0.000305A or .3mA, i'd be surprised if the LED even turns on at that current....
did i miss something here?
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My strategy was trial and error until I get the brightness correct while making sure I don't go over the maximum current indicated on the datasheet. It's difficult to calculate what the correct current is with a subjective measurement of "comfortable visibility".
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understood, from reading the datasheet, i would be really surprised if it turns on using a 10k ohm current limiting resistor. i am curious thought, is there a reason you are using that specific LED?
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something doesn't sound right with those LEDs, have you got a schematic for the board posted? what voltage level are you using to drive the LEDs?
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Using these ultra bright LEDs as indicators can be tricky - I always use at least a 1k resistor or, if not my design, a black marker. There are many gadgets with leds that wake me at night when they blink. Don't think it's broken.
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i looked at the datasheet for the LED, something doesn't sound right with that. the math doesn't seem correct to me...
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