The Little Knocker is a machine that produces strange knocking sounds. It consists of a solar cell, a motor, and several electronic components that you solder together yourself. When there is enough light, the motor rhythmically taps a small piece of wood, producing the knocking sound. In low light, it knocks only occasionally, while in bright light it knocks much more intensely.

The machine’s electronic control system is called “Sun-Eater.” It enables motors to be powered by small solar cells. Here’s how it works: The small amount of electricity generated by the solar cell is first collected in a capacitor, slowly charging it. Once it is full, the circuit reacts and transfers the stored energy to the motor. The motor twitches briefly, discharging the capacitor in the process. Now the charging cycle begins anew. What makes the machine special is that it can be built in a short time and then operates autonomously for many years.