Arduino Newbie - Max Input Voltage

Development Boards Arduino
1

Hey guys. I did a search and couldn’t find anything, and I’m new so I really hope I put this in the right forum. For a little background info, I’ve just started programming with Arduino and I have, more or less, beginner (intro college classes) experience with java and electronics.

Looking under the product information for the Arduino Uno board or various chips like the ATMega328, it’s mentioned that operating voltage is around 1.8v - 5.0V. Current projects I’ve been working on building are dealing with between 5 and 10 LEDs. I guess what I’m asking for is kind of a “dummies guide” approach to an answer. I’m understanding that the Uno or chips take a max voltage of 5V, correct? The reason I ask this is basically for this reason… let’s say that I’m wanting to hook up 10 LEDs that require 2V each. If those are in series, you’re looking at 20V needed to power the LEDs. I guess most people would be hooking them up like Christmas lights that don’t require the microcontroller, but if I’m blinking the lights to a random blink, fade, or flicker pattern, I’d need the chip. So how do you operate 20V worth of LEDs with a microcontroller that is supposed to take 5V max input voltage and (I assume) outputs a max of 5V on each of its pins?

When I look at the kinds of projects people come up with, various robots, an Arducopter, etc, it seems impossible that these projects are running off of 5V of power. It seems like there has to be a higher input voltage for these projects to work. I’ve seen wall warts that output 9V or 12V, but if you put that into the arduino circuit isn’t it going to blow the microcontroller? And if you’re having to use a 5V regulator to shrink the input voltage down from 12V to 5V, why not just buy the 5V wall wart power supply in the first place?

I know this is probably a really basic answer that most everyone knows and understands, but it seems when you’re looking for beginner guides to this kind of information all you get is “oh just plug in this LED, upload this blink program, and viola!” I haven’t been able to find solid conclusive answers about this from my searching. Some help and understanding on this would be greatly appreciated! I’d really hate to plug in a 9V battery or a 12V wall wart into my microcontroller LED circuit only to end up blowing up the microcontroller :shock:

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Instead of connecting the diodes in series you put them in parallel, with each their own current limiting resistor behind (or before) it. In parallel circuits the branches each have the same voltage across it. The total current going into the parallel circuit divides in to certain parts. So in your case each LED and resistor pair (a branch) gets 5 volt across it. The led takes it’s voltage drop from that, according to the datasheet and mostly based on color/chemistry, but also current. The resistor takes the remainder of the 5 volt, limiting the current based on Ohm’s Law. (yeah I know, current determines voltage which determines current and so forth, but the equation settles to some specific value) The resistor should be chosen such that the LED gets a safe amount of current through it. At the end of each branch, all those currents come together again. So you probably won’t be able to light a large bunch of LED from a single output pin. The pin can only supply so much. The datasheet of the atmega chip should provide how much.

Alternatively you could use a NPN transistor on the GND side of the parallel circuit, and switch it with a digital pin. Transistors can handle much more current than an output pin can supply.

LED calculator with example circuit:

http://led.linear1.org/led.wiz

3

Thanks for the reply, that definitely cleared up some of the confusion :). As for the input voltage… you can still only have 5V going into the chips though, correct? Any higher voltage would have to be regulated down to 5V or else the chip would fry right?

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SmokeGSU:
Thanks for the reply, that definitely cleared up some of the confusion :). As for the input voltage… you can still only have 5V going into the chips though, correct? Any higher voltage would have to be regulated down to 5V or else the chip would fry right?

Correct.

5

Don’t forget to search through the Sparkfun Tutorials, in particular these about voltage regulator/walwart use:

http://www.sparkfun.com/tutorials/103

http://www.sparkfun.com/tutorials/57

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Valen, these were exactly the kinds of tutorials/general information topics I had been looking for but unable to find. Thanks for the links!