If you like to y guitar, maybe you should try to do this with Guitar Hero Midi Controller. It uses well known Arduino board to interface Guitar with external MIDI device.

With the current version you can:

• play 2 octaves of an 8 note scale at a time;
• change the starting note anywhere in the range of a regular keyboard;
• change octaves’
• change keys;
• change tonal modes (Ionian, Mixolydian, Lydian, Dorian, Aeolian, Phrygian, Locrian);
• change the timbre of a sound;
• change the resonance of a sound;
• use the whammy bar to pitch bend;
• play chords in the mode you have the guitar set to (major/minor/etc.);
• rock out with a video game toy.

I think this is a great way to make your defective guitar useful. in order to make the program run, you’ll need a MIDI library and guitar library. Project is well documented and illustrated. It shouldn’t be very difficult to rebuild.

This is a small programmable device (similar to PLC) with 4 inputs, 4 outputs and full development system running under Windows.

You can write and test a simple program, with debug feature, then store such program in the device non-volatile memory and then, every time device powers up, your application starts autonomously. Project archive contains schematic, printed circuit board, HEX file ready to be uploaded to microcontroller and application program that runs on PC (Windows environment).

This device is very simple and can be built on simple prototype board, but its effect can be really annoying. It simple generates a short beep of very annoying frequency at random times (within half an hour to nine hours).

All you need is to hide a device somewhere and see the reaction of your friends. Project source code is written for AVR-GCC compiler and is simple to understand and use. Just be sure to enable CKDIV8 fuse in order to run attiny2313 at 4MHz from internal clock generator.

Electronics can be romantic. The Autonomous Parapoetic Device is a self-contained and portable machine that generates poetry. The idea is really great - electronics is packed in a nice wooden box. You just need to open it and 20×4 LCD screen shows poetry.

All this joy is driven by ATmega168 microcontroller programmed with Arduino (source). This could be great geeky gift for your beloved one.

It can remember 4 different loops. You can see which one you’re one on the 7 segment display and scroll to different ones with the rotary encoder knob next to it.  The tempo can be seen on the 4 LEDs in the lower right corner.

“There are 4 speaker terminals on the box, into each of which you can plug any object that can run on 5 volts. In the video I’ve plugged in LEDs because it makes the interaction clearer, but my main interest is in plugging motors in, attaching them to the box, and amplifying the sounds they make. Each speaker terminal has a button and a pot. Pay attention to which of the 4 tempo LEDs is on, then press a button, then let go. It will switch on the object (motor, LED, etc), then switch it off when you let go. The next time it cycles through the loop of 4 LEDs it will switch on and off at the same points. The object will pulsewidth modulate at different speeds depending on what position the pot is in when you switched it on.  You can do this up to 8 times and can change the PWM with each one, then do the same with the 3 other objects.”