Minecraft wiki entry for Pulse, associated text: This circuit uses a sticky piston and an observer to separate the rising from the falling edge of a signal. The rising edge powers the piston, lifting the observer above the redstone where it has no effect. Then, at the falling edge of the input signal, the piston retracts and the observer sends a 1-tick pulse via the redstone on the glass block. Note that the glass block is required to prevent this from turning into a clock.
Moved Observer FED - flat