Very basic questions about resistors


I'm a Arduino and Electronics newbie. I've been trying to learn a bit more from AC/DC power to circuits and everything that I need to know to make cool projects. I have some very basic resistors questions:

  • In this image, why is the resistor in that place and not connected to a LED or something instead of the ground?
  • When I'm designing a circuit do I have always to make all the math to be sure that there is resistance in the circuit? And from the + to the - how much resistance should there be?
  • When the Arduino is connected to a LED it needs a resistor, why doesn't it need a resistor when it connects to a chip?

Thanks! duarte

The resistor is in that place because there is nothing the switch is actually controlling only it's state needs to be used by the arduino for programming like if switch is ON then motor moves one way and if OFF moves the other way. as there is no actual electrical element controlled by it the current will be in excess at it's connecting point's that will more likely heat the switch.

yes definitely that needs to be calculated ,however not that correct it's needed i mean if about 420 ohms resistance is needed then you can go with about 500,520 ohms resistance it's Okey.

Because the chip that's used in there is actually a H - BRIDGE that can accept voltages Between 3or 5v to 36 volt DC and an LED can't ,However depending on it's MM.


(or go to college! XD)

Thanks for the fast answer :D

A couple more:

How do I know how much resistance is needed so that a circuit doesn't heat up or break? What is MM? Do I always have to check the values in the datasheets? Will datasheets always seem this strange and indecipherable?


P.S.: in college... but a computer geek, it's harder to break and burn things :P

I think he meant millimeters, as a larger LED should be able to handle higher voltages…

I may be wrong, but isn't that resistor there used as a pull down resistor? When the switch is on, the input 2 will get a +5V, but with the switch off without the resistor, it will float; the resistor to ground will ensure a non floating input. The resistor chosen is to ensure the current draw isn't over the limits.

Thank you! :* I just fell in love with this forum with all this answers. Some of the stuff I'm not really sure what you mean, but I bet I can read it somewhere on the interweb.

Thank you, I'll be coming back.

Hello DARAGAO, ALL these people who posted above are nice! and very eager to help and will always go like this ,because we are the people who love to STUDY,this is What is mean't by a Engineer or Simply a Curious Mind.

Best Regards, Nishant Sood

and KEG7..........(how you formed this CODE!)......You are right!.....It's not Mickey Mouse(Atleast that comment was worth few nice loud laughs!)