We almost skimmed right past this spooky HDD activity light thinking it was just another set of LEDs wired to the motherboard. However, they explained right off that they didn’t want just another blinking light on their case. They wanted it to change its intensity smoothly based on hard drive activity. While there are a million ways this could have been over engineered, we think they did a pretty good job of simplifying the circuit. The bill of materials is pretty much just a handful of resistors, LEDs, an opto isolator, and a capacitor. The effect, is quite nice and can be seen in the video after the break.
[via Hacked Gadgets]