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1

Hello,

I’m pretty new to Arduino. I have the Sparkfun inventor’s kit and have been slowly but thoroughly going through it.

To supplement this I have been learning as much about electricity from the Sparkfun tutorials as I can. But there are still some things I can’t quite wrap my head around.

For instance, why is a voltage divider necessary to to lower voltage, why not just use a single resistor?

Theres a ton to learn, and many of the tutorials say that you should read a different one first before reading that one, but then the other ones say you should read that first one before reading it. Where do I start? I’m usually a fast learner, but there seems to be a threshold of comprehension that i haven’t quite gotten past with this.

Any help would be greatly appreciated.

Thanks,

-Elliot

2

elliotsl:
For instance, why is a voltage divider necessary to to lower voltage, why not just use a single resistor?

[http://en.wikipedia.org/wiki/Ohm's_law](http://en.wikipedia.org/wiki/Ohm%27s_law)

http://en.wikipedia.org/wiki/Kirchhoff’s_circuit_laws

3

Hi,

I think you might enjoy reading this book. It includes a ton of great information that spans a wide assortment of concepts and ideas that are helpful in electronics.

https://www.sparkfun.com/products/9458

09458-01a.jpg600×600 82.4 KB
https://cdn.sparkfun.com//assets/parts/ … 58-01a.jpg

4

Thank you, I will definitely check out that book.

5

elliotsl:
Hello,

For instance, why is a voltage divider necessary to to lower voltage, why not just use a single resistor?

-Elliot

Happy learning! Glad to help. But yes, reading the right texts/tutorials is the way.

Start with Ohm’s Law - that deals with basic voltage, current and resistance (E,I,R).

E = IR

and all the algebraic variations.

Your question about a voltage divider… you need two so that you know the ratio of the two resistors.

Add the two resistors’ values and use Ohm’s law above to get I, given you know E (say, 3.4V).

If the ratio of the two was, say, 10:1, then the voltage across the smaller resistor would be 1/10th of the voltage across the two resistors.

6

stevech:
If the ratio of the two was, say, 10:1, then the voltage across the smaller resistor would be 1/10th of the voltage across the two resistors.

While stevech's encouragement is sound, it is also an example of the subtleties that require close attention.

The resistor divider is dependent upon the ratio of each resistor to the sum of both, not the ratio to each other. In stevech’s example the voltage across the smaller resistor would be 1/11th not 1/10th. If you want a divider of 1/10th using two resistors, one would need to be 9 times the value of the other.

In addition, the answer to why you can’t just use a single resistor is that actually you can! At least under certain circumstances. It depends upon the input impedance of the receiver of the signal. And even if you build a two resistor divider you might not get the intended result if you don’t take that input impedance into account (tho with today’s CMOS inputs the effects are frequently negligible.)

That level of complexity and subtlety is one reason why this stuff is so much fun to learn and work with.

As stevech said, Happy Learning!

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