First, yes I've unplugged the power source.

Second, I'm an electronics newbie so please be patient.

Finally, I'm working on a project and I think I may have a short. But I'm not understanding why.

The project: An LED strip with a dimmer.

The problem: My breadboard was burnt and slightly melted along the positive and ground lines closest to the power source. Here is what the breadboard looks like:


Here is a diagram I wrote up (hope I got that right; it's my first attempt).

electronics diagram

  • LED = Neopixel RGBW 60 pixels/meter 1m strip
  • MC = Arduino Pro Mini 3.3V
  • AC = 120 V AC wall outlet
  • DC = AC to DC power converter 5V
  • C = 1000μF capacitor
  • R = 390 Ohm resistor

More documentation: https://github.com/coreyferguson/workbench/tree/light-dimmer-only/lighting

Any help would be much appreciated!

  • 6
    \$\begingroup\$ It appears that the big electrolytic capacitor is connected backwards - the arrows on the side of the capacitor point to the negative end - you appear to have that end connected to the positive supply. \$\endgroup\$ Jan 11, 2017 at 3:06
  • \$\begingroup\$ Maybe your jumper leads from the barrel connector accidentally touched the other rail? \$\endgroup\$
    – tangrs
    Jan 11, 2017 at 3:11
  • \$\begingroup\$ cap arrow points to -ve but is connected to + but the rails on outside are not connected. Two big problems. \$\endgroup\$ Jan 11, 2017 at 3:20
  • 1
    \$\begingroup\$ I think he pulled the jumpers between the connector and the rails so that the burn marks would be more visible. \$\endgroup\$ Jan 11, 2017 at 3:33
  • 1
    \$\begingroup\$ Electrolytic capacitors are polarity-sensitive - if connected with the wrong polarity, the very thin insulating layer on the electrodes will be damaged, and the capacitor will become a very low value resistor - your capacitor probably acted as a short circuit. The arrows on the capacitor point towards the negative terminal, not "how the electrons flow". \$\endgroup\$ Jan 12, 2017 at 2:46

1 Answer 1


As peter says. That capacitor is backwards,

after identifying the positive and negative ends mark them with red and black permanent marker or some paint. or plastic insulating sleeve from some wire. it'll save more hassle in the long run.


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