I wanted to reuse a ICSP pin for a status LED, so looked to the Uno schematic for guidance (www.arduino.cc/.../arduino-uno-schematic.pdf) since it has the D13 LED parallel to SCK.
Was wondering what's behind the design choice to have 1k current limiting resistors (RN2C, RN2D) on the RX & TX LEDs parallel to D0/D1, but 500 Ohms for D13 and the power LED courtesy of two parallel 1k resistors (RN4D, RN4C & RN2A, RN2B)? Is this purely aesthetics in keeping the RX/TX LEDs dimmer, or are the serial lines more susceptible to interference from these LEDs?
Also, is it purely a manufacturing choice to use additional 1k resistors in parallel rather than 560R single components as the resulting current through the LED would be very close?
strykeroz:
Is this purely aesthetics in keeping the RX/TX LEDs dimmer, or are the serial lines more susceptible to interference from these LEDs?
No idea.
My annoyance is that the power LED for starters, is way too bright.
strykeroz:
Also, is it purely a manufacturing choice to use additional 1k resistors in parallel rather than 560R single components as the resulting current through the LED would be very close?
That RX resistor may prevent frying the 16U2 and/or 328P when a user decides to set the RX pin high (or low) and the opposite is driven from the 16U2. A 250 Ohm should protect the two AVR's but back in the FTDI days, a higher value may have been needed (just guessing, I didn't look at the datasheet).
Update: I was thinking about the 1k resistor on the RX line itself, my own little tangent I guess.
big fuss over nothing. modern led is so efficient anything from 100ohm to 10k works fine. the biggest problem for me too is even with 1k they are so bright you cant see anything else on the board. as far as safety the truth is contrary to popular opinion even dead short to gnd is unlikely to "brick" an avr or significantly reduce life let alone through an led. unfortunately the same may not be true of the poor led (depending on type).
john1993:
as far as safety the truth is contrary to popular opinion even dead short to gnd is unlikely to "brick" an avr or significantly reduce life let alone through an led.
Ooooh, you will be in trouble saying that!
john1993:
post count 666. hope that's not an omen.
Was 667 when I read it. Clearly you have had more to say!
yes, i definitely find those annoying. specially on my usbasp and serial adapters. however nothing a dab of wet 'n wild creme noir (#424a) dont fix.
i am convinced its overvoltage not overcurrent which kills chips. but you are right about saying any more. last time the entire thread was deleted due to hysteria and ego which is not fair to op. it was probably my snarky comment about "ohms suggestion" that did the trick. anyway time to shut up on that subject. although back then my karma did get bumped up 2 points by silent (but knowledgeable) minority so maybe worth the risk.
ps. i notice karma just got bumped up another couple. lol
ok, WHO is doing that? i try my best to keep that number low by being mean and sarcastic. maybe accidentally informing and assisting by accident on occasion but SOMEBODY is spoiling all my fun. if i have to dig out that shift key from under the bed one more time... you have been warned!!!
was it you doc? i did get that pm. lol
i hate to drift back on topic but somebody (apparently allergic to google) asked me what the wet 'n wild was. its black nail polish. no matter how much you put on the led it never completely blanks but can dim it to a tolerable level. much cheaper and safer than "a small chisel".
