This is the circuit I used for my HDD Activity Monitor, it is usefull when doing PC mods to add LED effects. This does not display the actual data transfer rates, just how hard the drive is working, the more LED's lit, the more activity. closing SW1 will put it in dot mode, leaving SW1 open puts it in bar mode.
This is the typical circuit I use to connect a 3mm LED to any PIC microcontroller, it is usually best to do it this way, PIC's usually would rather sink than source current. To turn the LED on just set the appropriate pin to LOW, to turn it off, set the pin HIGH.
Here is a simple Optocoupler interface I use to seperate / isolate a microcontroller pin from a higher voltage load such as a 12 Volt DC Relay.... Differrent types of optocouplers are available to accomodate any interface isolation you may need for your circuit.
Here is a simple Infrared remote tester circuit, it comes in handy when needing to test output of an IR emitter or any IR remote control