Arduino Forum

Products => Arduino Due => Topic started by: skyjumper on Jan 10, 2013, 06:37 am

Title: LED Brightness
Post by: skyjumper on Jan 10, 2013, 06:37 am
I'm feeding my Duo with about 6.6VDC, and I find that the PWR and L LEDs are quite dim. Is this normal?
Title: Re: LED Brightness
Post by: Leon Heller on Jan 10, 2013, 11:53 pm
The LEDs are driven from the 3.3V and are rather dim. Check the schematic to see how much current they are taking.
Title: Re: LED Brightness
Post by: Void_Ptr on Jan 12, 2013, 02:50 am
The 6.6v you are feeding the Due goes through a voltage regulator and pared down to 3.3v before getting fed into the chip. The digital pins (I'm assuming you are doing PWM?) are at 3v3, as mentioned by Leon. It is also possible that your resistor (you are using one, right?) may be too large depending on the voltage rating on the LED. Not all leds are created equal.
Title: Re: LED Brightness
Post by: skyjumper on Jan 12, 2013, 10:07 am

The 6.6v you are feeding the Due goes through a voltage regulator and pared down to 3.3v before getting fed into the chip. The digital pins (I'm assuming you are doing PWM?) are at 3v3, as mentioned by Leon. It is also possible that your resistor (you are using one, right?) may be too large depending on the voltage rating on the LED. Not all leds are created equal.


Thanks for the reply. I was referring to the PWR and L LEDs, which are built on to the board.
Title: Re: LED Brightness
Post by: Void_Ptr on Jan 13, 2013, 06:50 pm
Ah, so yes, there is a resistor on those. The documentation for the board says that you should feed between 7v-12v through the barrel jack, since the voltage regulator loses a bit when it steps the voltage down. Does it look brighter when you power the board through the USB? (5v, bypassing the regulator, iirc). If not, then, that's how bright they go. ;)

-r
Title: Re: LED Brightness
Post by: Leon Heller on Jan 13, 2013, 07:00 pm
One pin is driven from an ARM output, altering the supply voltage won't make any difference to the brightness. Most pins can only supply 3 mA. The power LED is probably driven from the regulated 3.3 V supply, and should remain the same.
Title: Re: LED Brightness
Post by: mantoui on Jan 14, 2013, 09:52 pm
The HC pins can source/sink  15/9 ma.  The LC pins only provide 6/3 ma.  See the "pin out diagram", the first thread in the DUE forum, for which pins are HC.  If you want to drive your LED at 20ma, you'll need a transistor or IC