Most of us have given up our big, bulky stereos in favor of smaller, sleeker models, but how many of us actually get rid of the old ones? If you don't like the idea of throwing out or giving away electronics you spent good money on, you can always upgrade them instead!
PC486 saw an opportunity to give his roommate's old Panasonic stereo some new functionality, so he did some reverse-engineering and added Bluetooth capability so that he could control it with his smartphone.
Since his roommate said no to modifying the hardware, he figured out a way to use a microcontroller and an infrared LED to send commands to the stereo. He soldered a field-effect transistor onto a piece of breadboard and added a 3.5mm audio jack to the ABS case for the LED output.
Finally, he installed a Logitech audio receiver and the project was finished. He can turn the stereo on and off, as well as feed it music, all through his smartphone. Who says you can't teach an old stereo new tricks?
Want to try it yourself? You can find detailed instructions, as well as the source code for the microcontroller, on his blog.