erco
Senior Member
******************* Worst practice observation follows. *****************************
I slammed together an 5V 20M2 RGB LED project lately without current limiting resistors and it works just fine. Three output pins drive a parallel PAIR of 10mm RGB LEDs. TTYTT I did put one resistor onto green just to balance the color intensity and get a better white. No PWM, just full power high/low. Working great, even though each pin is outputting some 50-60 mA, occasionally all 3 pins on at once for white. I'm fully aware I'm pushing it and operating outside the recommended parameters. I was in "git her done" mode to film a video. I had good intentions to rectify (!) the LED problem later and add resistors before something burned up but it's still working, if only for a few minutes at a time. Someday I'll wire up a similar non-critical circuit and do a continuous destructive test.
I used to get my knickers in a twist worrying that a Picaxe pin can sink more current than it can source and build the circuit accordingly. I'm starting to wonder if it matters. The internal impedance self-limits current at some point. Of course a dead short would led more current flow, but any LED will drop 2-4 volts and the internal impedance can drop the rest. Deal?
Of course I'm pushing my luck and Hippy and Technical can't condone my actions, I'm just curious if anyone has actually burned up an output pin from too much current.
I slammed together an 5V 20M2 RGB LED project lately without current limiting resistors and it works just fine. Three output pins drive a parallel PAIR of 10mm RGB LEDs. TTYTT I did put one resistor onto green just to balance the color intensity and get a better white. No PWM, just full power high/low. Working great, even though each pin is outputting some 50-60 mA, occasionally all 3 pins on at once for white. I'm fully aware I'm pushing it and operating outside the recommended parameters. I was in "git her done" mode to film a video. I had good intentions to rectify (!) the LED problem later and add resistors before something burned up but it's still working, if only for a few minutes at a time. Someday I'll wire up a similar non-critical circuit and do a continuous destructive test.
I used to get my knickers in a twist worrying that a Picaxe pin can sink more current than it can source and build the circuit accordingly. I'm starting to wonder if it matters. The internal impedance self-limits current at some point. Of course a dead short would led more current flow, but any LED will drop 2-4 volts and the internal impedance can drop the rest. Deal?
Of course I'm pushing my luck and Hippy and Technical can't condone my actions, I'm just curious if anyone has actually burned up an output pin from too much current.