Digital Scratch Pad

"Digital Scratch Pad" was made using a 555 timer IC . The sound is controlled through a photo-cell which is sensitive to light. As you cover the photo-cell, the the sound gets deeper, and as the cell is exposed to more light, the pitch gets higher. Underneath the felt is a flex sensor. The more pressure you place on the felt, the more it distorts the sound. There is a 1/4 inch jack, so you can plug it into an external speaker to make it louder. I've used this plugged into a Marshall stack, and it sounds awesome.