Hi to all.
Recently I've been forced to move from Arduino Mini Pro 5V to the 3.3V version. Today I've discovered how is hard to make an adafruit white LED bright with so low voltage.
By using a (chinese) stabilized power supply at 3.3V I have verified that I can obtain around 25 mA of flowing current in the LED with just a 10 Ohm load-resistor connected to ground. This make the LEd very bright that is what I'm looking for. Unfortunately, when I connect the led to a pin of Arduino the, current falls down to the miserable value of 8.71 mA :o :o :o
I've tested digital and analog pins, the result doesn't change: without any LED I measure around 3.25 Volt when the pin is at HIGH value, after connecting the LED+resistor the voltage drops at 2.97 V. That voltage is absolutely not enough to make the LED working well since the the forward voltage I measure is 2.85V.
But, but, but, but... if I connect the LED to directly to the Vcc pin of Arduino... bang! I measure 18.7 mA of current and the light intensity become (almost) acceptable. So that minimal difference in voltage makes the LED working in a reasonable way.
- Why the voltage at output pins goes down when a load is attached?
- How I can power the LED with voltage at Vcc and, at the same time, turn it on/off?
- There is any bright LED with lower forward voltage the 3V???
p.s: below some measurement I've made with the Adafruit Super Bright White led. Maybe they are interesting for somebody.
PWR R I FV Note (volt) (ohm) (mA) (volt) ----------------------------------------------- 2.97 40 6.28 ? pin #2 2.97 20 7.69 ? pin #2 2.97 10 8.71 2.85 pin #2 2.97 5 9.31 ? pin #2 2.97 0 9.97 ? pin #2 (for few seconds) 3.25 10 18.7 3.03 Vcc pin 5 120 15.5 2.99 stabilized power supply device 5 100 17.9 3.05 stabilized power supply device 5 50 31.1 3.25 stabilized power supply device
(FV = forward voltage)