LED's & Resistors

[kcofohio]

I'm building a 5v usb box mod to go with modded 5v PT. Space is very limited, so I thought that I'd use 1 resistor piggy-back to 2 led's on the neg. lead. One led is for the master switch, the other is for PT switch. It seems that only 1 led will light up at a time.
I used this layout, MadVapes e-Cig 'How To' Tutorials • View topic - My 3xAA 5v Box Mod
Will I need 2 separate resistors? Thanks

 

[Java_Az]

You can use one resistor if the LED's are wired in series. But you would need to calculate the proper value resistor to use. By piggy back i am guessing you have them wired in parallel. You should have separate resistors for each LED if wired in parallel . Here is a link to a page that ha some good LED info on it. Light Emitting Diodes (LEDs)

To use one resistor you can wire in series like in the image

Not a good idea to wire LEDs like this. each LED should have it's own resistor if wired in parallel.

 

[kcofohio]

Thanks for the link, Java. Using 1 3mm red, and 1 3mm green led. Together they need 220 ohms resistor. I'm using a 470 ohms.
My thinking is/was that since each led has its own separate + supply, the - side would matter since it is constant, therefore the resistor would be there for each when needed. But hey, I've got a lot to learn.