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### Topic: General project question concerning resistors (Read 4226 times)previous topic - next topic

#### dougmon

##### Mar 31, 2014, 01:22 amLast Edit: Mar 31, 2014, 01:32 am by dougmon Reason: 1
I don't know if the belongs in this section or in general electronics, but the question came up while I was reading the Projects Book, so I thought I'd ask it here. This is coming from a total electronics noob, so please, use small words and easy concepts.... :~

On many of the projects, there is a resistor between the ground leg of an LED and ground on the breadboard. I am assuming this is so that there will be the lowest possible energy at ground -- is this correct?

Thanks for any constructive answers.

Doug

#### retrolefty

#1
##### Mar 31, 2014, 03:20 am

I don't know if the belongs in this section or in general electronics, but the question came up while I was reading the Projects Book, so I thought I'd ask it here. This is coming from a total electronics noob, so please, use small words and easy concepts.... :~

On many of the projects, there is a resistor between the ground leg of an LED and ground on the breadboard. I am assuming this is so that there will be the lowest possible energy at ground -- is this correct?

Thanks for any constructive answers.

Doug

A resistor in series with an led is used to control the amount of current that can flow through the led to keep it at or less then the led's maximum rated forward current. As it is a simple series circuit it does not matter if the resistor is wired before or after the led, just that it exists and is the proper value for the applied voltage used and the rating of the specific led used.

#### dougmon

#2
##### Mar 31, 2014, 04:29 am

I don't know if the belongs in this section or in general electronics, but the question came up while I was reading the Projects Book, so I thought I'd ask it here. This is coming from a total electronics noob, so please, use small words and easy concepts.... :~

On many of the projects, there is a resistor between the ground leg of an LED and ground on the breadboard. I am assuming this is so that there will be the lowest possible energy at ground -- is this correct?

Thanks for any constructive answers.

Doug

A resistor in series with an led is used to control the amount of current that can flow through the led to keep it at or less then the led's maximum rated forward current. As it is a simple series circuit it does not matter if the resistor is wired before or after the led, just that it exists and is the proper value for the applied voltage used and the rating of the specific led used.

Ok, I am one confused noob now. If the resistor runs from cathode to ground, it affects the voltage going to the anode?

I took a look at the circuits I was referring to, and it seems that there is a resistor to ground only when there is a jumper from an output pin going to the anode. Perhaps I'm missing some info in my question. I'll do more research. I'm just trying to understand the circuits I'm building. Perhaps that will come with more experience.

#### jn-wp

#3
##### Apr 01, 2014, 01:18 am
trying to understand what you build is a good idea!
and sure: you will understand the more you build with electronics...

perhaps you should start with a beginner book about electronics?!?
the arduino project-book is great, for building some arduino-projects.
but it doesnt provide much background-information, about what you are doing!

learn something about voltage, ampere and resitors in generall.

to your question: your led will break if the current through it is too high! (and led is at least a diode and a diode has no resistance in "through-direction"!) so with ohm law u=r*i you can calculate, that the current i is very high if the resitor r is low.

so you have to put an extra resitor in you circuit. but as retrolefty allready said: it doesnt make a difference if the resistor is between anode an output-pin or kathode and ground!

Quote
and it seems that there is a resistor to ground only when there is a jumper from an output pin going to the anode

of course: if there is no output, there is no voltage on that pin and no current is flowing. so you dont need a resistor!  XD

#### dougmon

#4
##### Apr 01, 2014, 04:54 am

trying to understand what you build is a good idea!
and sure: you will understand the more you build with electronics...

perhaps you should start with a beginner book about electronics?!?

Quote
and it seems that there is a resistor to ground only when there is a jumper from an output pin going to the anode

of course: if there is no output, there is no voltage on that pin and no current is flowing. so you dont need a resistor!  XD

And this is exactly where I am -- perusing a beginners electronics book. And a beginners book about building circuits.

I thank you all for sharing your knowledge, and for the advice you've given me. I'm the type of person who can't really repeat something (like a circuit) outside of its initial context unless I understand how it works. So...thanks again, everyone who answered.

#### jn-wp

#5
##### Apr 02, 2014, 01:59 am
so good luck with learning electronics!
there is a extra part in this forum about question on general electronics...
perhaps you can find some help there if you have any further questions?
cu soon! ;-)

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