As I consider myself being a geek, I keep my old stuff, and also collect used and partially broken stuff.
Many of us changed often the mobile phone or cell phone... whatever you call it. I have a Nokia 1100 with it's microphone broken. So I tought it can be useful for something in the future.
I used only recovered parts for this project!
P.S. Sorry for poor photo quality... were made using another... mobile phone. :D
Step 1: What you need
2. one charging plug (it can be used the phone charger's original one)
3. two terminals miniature sockets and cables with miniature connectors
4. some old computer case front panel cable connectors ( I used Hdd Led, Power Button, Reset Button connectors) and front panel socket like (you can use jumperpins instead)
5. any small old electronic board (PCB) or perforated board (I used an old Philips TV small module PCB)
6. omron 12v miniature relay (with at least one pair of contacts)
7.one BC548 NPN transistor or equivalent
8. one 1N4001 diode
9. one opto-isolator with NPN transistor output. I used EL817 optoisolator from an broken ATX computer supply
10. one 470uF/10v capacitor