SpookGoblin
Offline

I'm trying to backlight some buttons on an NES controller and I can't seem to get them to light up.  While I've referenced a few articles regarding which terminals to solder what to, but otherwise, I've been flying solo in hopes of accomplishing something by myself.  Alas, such futile efforts.  Can anyone tell me why my LEDs aren't illuminating?  I have the positive lead wired to the positive terminal of the first LED with its negative connected to the positive of the next and so on until the negative of the final LED is connected to the ground terminal. 

I've attached a picture to illustrate, but I apologize in advance for the crappy picture.

Any help would be super appreciated!  I'd like to get this done ASAP!

TylerBarnes
Offline
Dallas, Texas

You should not be wiring those in series like that. There is not enough voltage to drive that many leds. Also you need current limiting resistors on each led.

Fist of all what color are the LEDs? This will give me a ballpark figure for what the forward drop voltage is across each led.

For now I will assume they are blue, with a common voltage drop of 3.3v.
Each LED needs its own risistor and they should all be wired in parallel, not in series like you have it now.

The provided schematic will give you about 10mA on each led.
using no resistor will cause the LEDs to try and pull way more current then they are capable of handling. You might need to use some new LEDs if you pop these ones you have in there currently

Also if you change the number of LEDs used. The value of the resistor must change as well. For example the resistors values for the following number of LEDS include:
1 LED=180Ω
2 LEDs= 100Ω
3 LEDs= 68Ω
4 LEDs= 47Ω
And so on.

Last edited by TylerBarnes (Feb 10, 2015 6:50 am)