May 1st, 2013 marked the birthday of my beautiful daughter Nadia Sophia. As such, most of my tinkering seems to revolve around fixing and improving the stuff that we use for her. A friend of ours gave us a used vibrating Baby Bouncer. Upon installation of one of those hideously expensive (and wasteful) "D-Cells", much to my delight, nothing happened! I LOVE an excuse to pull something apart, add some extra goodies, and then put it back together. My long suffering wife just rolled her eyes when she saw the look of excitement on my face.
The Mennonite inside of me couldn't bare the thought of continuously reloading and discarding those D-Cell batteries. Being the typical tinker, I have a drawer full of wall-warts. A broken toy is the perfect excuse to use up some spare junk lying around, and learn something new.
Cracking open the case revealed a simple circuit consisting of a motor, and a switch. The motor is a small DC brushed affair, with an eccentric weight on it. When the eccentric weight rotates about the motor shaft, vibrations are created due to an unbalance. This effect is very similar to a car wheel running unbalanced.