This is a great sleeping prank -- It might be found on the first day, or several weeks from the implementation. It's the perfect prank.
Difficulty: Easy, but involved. (ability to solder and use a multi-meter helps)
If you decide to do this prank, understand that it could be a career-limiting move if it is done on your boss and/or somebody without a sense of humor. I would also recommend experimenting with a dummy keyboard that you don't mind destroying first.
True, most people don't use caps lock very often, if ever, but unfortunately not many other keys are linked to an LED. Also most keys are only pressed momentarily, which would require a more complicated circuit to work effectively. The num lock LED turns on and off several times during boot time, so that's out which only leaves the caps lock as a viable solution.
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Origin of this Project
This was originally posted on on my blog (before KipKays video):
Step 1: Setup
1. Screw drivers (Phillips and a wide slotted)
2. Needle nose pliers
3. Soldering iron + solder
4. Thin wire (22 gauge works well)
5. NPN transistor
6. Electrical tape
You can get all these from your local RadioShack.
I bought a CoolHeat soldering iron for this project due to its great portability. If you get one of these be sure to purchase at least 2 replacement tips since they’re brittle and WILL break during normal use.