At the moment, I've just hooked up one LED, which I'm powering from the "Vin" pin with a 5V regulated wall-wart (1.2A). The datasheet says that each LED will draw 50mA max at 5V and this single beast seems to work fine.
If I wanted to make a chain of two, three, four, ... of these in the same way, is it still ok to power them from the wall-wart via Vin? I can't find anything that says the maximum allowable current and I don't want to fry anything. At the moment, I'm just getting the feel for how the LED library would operate with other code as it's quite specific for timing and requires interrupts disabled, so I'm feeling my way and don't have a firm project in mind yet. I'm just exploring possibilities.
I sort of feel it would be safer to eventually power the LEDs separately and take a feed from that to power the Uno but I'm not 100% sure about how to decouple things - any advice would be welcome if you think I'm heading for trouble. Eventually, I want to be able to drive a chain of at most 16 LEDs.
You need to feed 7-12v to the input barrel to power the voltage regulator which can source 800 ma at 5v to the arduino and 5v pin under ideal conditions. Same goes for sourcing power to the Vin pin except you have no polarity protection. You can plug a well regulated 5 v source directly into the 5v pin and also run your LED's off the 5v pin. If you feed 7-12v into the barrel, Vin will supply about an amp at whatever input voltage you provide minus .5-.7v loss incurred by the protection diode.
seanz2003:
You need 7-12v on input barrel to power the voltage regulator which can source 800 ma under ideal conditions.
I see - thanks! Am I just lucky that everything works with a 5V supply into the barrel jack and no USB connected? If I give it 12V instead but want it to still deliver 5V from Vin, I guess I need to drop the voltage to my LED(s) with resistor(s)?
seanz2003:
You need to feed 7-12v to the input barrel to power the voltage regulator which can source 800 ma at 5v to the arduino and 5v pin under ideal conditions.
"under ideal conditions" being 7V to the input barrel, not 12V.
fungus:
What you could do is grab a multimeter and measure the voltage at the 5V pin - see how much you're actually getting.
Ok, but I'm taking power from the "Vin" pin, which (as far as I could understand the schematic) comes directly from the barrel jack? If you read what it says on the web site about the LEDs, they can explode with anything >5V so I'm very wary of plugging in anything other than a 5V supply.
Yes lucky that vreg would power the arduino. If put twelve into the barrel you'll get slightly less than 12 at Vin- no good for addressable leds. Just plug your LED's into the 5v pin. You'll be limited to maybe .5 amp or so from the regulator. Better to just power everything from the 5v source.
seanz2003:
Yes lucky that vreg would power the arduino. If put twelve into the barrel you'll get slightly less than 12 at Vin- no good for addressable leds. Just plug your LED's into the 5v pin. You'll be limited to maybe .5 amp or so from the regulator. Better to just power everything from the 5v source.
Thanks again - so just to recap, I could safely set my wall-wart to 9V (0.65A), plug that into the barrel jack, but then take the power to the LEDs from the 5v pin instead of Vin? Then I could play with up to 10 LEDs (at 50mA max each) without risking the Uno or the LEDs?
RogerRowland:
Ok, but I'm taking power from the "Vin" pin, which (as far as I could understand the schematic) comes directly from the barrel jack?
So ... the LEDs are OK but the rest of the Arduino is probably getting less than 4V.
RogerRowland:
If you read what it says on the web site about the LEDs, they can explode with anything >5V so I'm very wary of plugging in anything other than a 5V supply.
That's what multimeters are for - measuring voltages before you connect things.
If you have a regulated 5V supply you can bypass the regulator. I'd get an old USB cable and cut the plug off. Power the Arduino through the USB socket instead of the barrel jack.
RogerRowland:
Thanks again - so just to recap, I could safely set my wall-wart to 9V (0.65A), plug that into the barrel jack, but then take the power to the LEDs from the 5v pin instead of Vin? Then I could play with up to 10 LEDs (at 50mA max each) without risking the Uno or the LEDs?
Yes.
Test the voltage regulator with your finger. If it burns you ... it's too much current.
Yep that's the idea. It is hard to say what the actual current will be that the vreg will source at 9v. Temperature plays a major role since the regulator will shutdown as it goes into thermal overload. Doesn, t necessarily hurt anything, but it is best to avoid frequently over stressing the part. The Basic rule of thumb is if the part is too hot to keep your finger on, you're probably overdoing it.
Yes; Vin is after the reverse polarity protection diode and before the regulator.
See the Uno schematic at the Products page.
The regulator will get noticeably warm with 12V input, and if a lot 5V current is being used it will get hot - too hot and it will go into thermal shutdown - or worse case, fail outright.
Your output voltage is probably 5V-1v=4v.
You led forward voltage is less than that so it has no problem turning on.
As already stated, if you are using a 5V supply, you should connect it directly to the 5V pin NOT to the barrel jack.
