I have a 5V adapter that reads 5.25V when testing it; not sure if it's "regulated." Is it okay to have that extra .25V going directly to a VCC /5V pin, or does it have to be exactly 4.99 - 5.0V? I think I read somewhere that you can actually plug in 6V into the VCC / 5V pin? Is that a thing? If so, will it shorten the lifespan of the arduino / pin?
This is common in phone chargers to improve charging speed by compensating for resistive losses in the often low quality USB cables. 0.25v is small enough that it's within spec for almost everything designed for 5v.
It is typically OK (the microcontrollers in the uno are spec'ed up to 5.5v, 6v absolute max).
You can if you're scared hack a cable and put a schottky diode in series with the +5v line - this will drop ~0.3v bringing the voltage much closer to the target 5v.
DrAzzy:
This is common in phone chargers to improve charging speed by compensating for resistive losses in the often low quality USB cables. 0.25v is small enough that it's within spec for almost everything designed for 5v.It is typically OK (the microcontrollers in the uno are spec'ed up to 5.5v, 6v absolute max).
You can if you're scared hack a cable and put a schottky diode in series with the +5v line - this will drop ~0.3v bringing the voltage much closer to the target 5v.
Thank you for your help.
About the diode, do you mean putting the anode of the diode to the + of the adapter, and using the cathode as the + connection?
Yes.
So the banded end of the diode (cathode) connects to your arduino. If you have a capacitor 0.1µF or so it would not hurt to put it after the diode, closest to the arduino (to ground)
JohnRob:
Yes.So the banded end of the diode (cathode) connects to your arduino. If you have a capacitor 0.1µF or so it would not hurt to put it after the diode, closest to the arduino (to ground)
Gotcha. Thank you.
Could I technically put an LED instead of the diode? Would the forward voltage make the adapter output only around 3V?
toxicxarrow:
Gotcha. Thank you.Could I technically put an LED instead of the diode? Would the forward voltage make the adapter output only around 3V?
No, you can't use an LED - the voltage drop is much higher, several volts, so the board probably wouldn't work. And even if it did (at an out of spec voltage), the LEDs you have lying around are probably only rated to 20mA, so if the arduino was able to run, the current that would have to flow through the LED would burn out said LED.
If you go the diode route, use a schottky diode, rated for 1A minimum. If you don't have some of these in stock, you should - they're a common, cheap, and useful component for any electronics hobbyist.
DrAzzy:
No, you can't use an LED - the voltage drop is much higher, several volts, so the board probably wouldn't work. And even if it did (at an out of spec voltage), the LEDs you have lying around are probably only rated to 20mA, so if the arduino was able to run, the current that would have to flow through the LED would burn out said LED.If you go the diode route, use a schottky diode, rated for 1A minimum. If you don't have some of these in stock, you should - they're a common, cheap, and useful component for any electronics hobbyist.
Ahh, the mA limit for LED, got it. How do I know if it's a "schottky" diode? I have a couple of these:
How do I know if its rated for 1A?
Don't create problems.
5.25volt is safe.
Consider powering the Arduino (Uno?) with a USB lead connected to a phone charger with USB socket.
Leo..
Wawa:
Don't create problems.
5.25volt is safe.Consider powering the Arduino (Uno?) with a USB lead connected to a phone charger with USB socket.
Leo..
Oh, for sure, I'm definitely using the 5.25V adapter. At this point I'm just soaking up information! 
That diode is a 1Amp type (size).
Most common standard diodes are the 1N4001 - 1N4007.
Most common schottky diodes are the 1N5817 - 1N5819.
Wise to have a bunch of the 1N4004 and the 1N5819 for your experiments.
Add "datasheet" to your Google searches, to see their specifications.
Leo..
5.25V is perfectly safe. Don't bother with the diode.
To find out its type, look at the printing on the housing. For it's size probably a 1A type indeed. Could be a 1N400x, could be a Schottky, or something else - no way to say from the outlook. You need the part number.