The 555 is a monostable that wants a negativegoing trigger. If the pulse you`re feeding it with is positive-going, you can run it through an inverter made up of either an inverting gate or, if you`re tight on space, a single transistor. Both ways are shown. The circuits shown in Fig. 25-9b are edge detectors as well, and are usually referred to as half monostables, since they can`t be used in every application.
Edge-detector - schematic

The width of the output pulse is determined by the RC value, but there are a few rules governing their use: The input pulse has to be wider than the output pulse. The input pulse can"t be glitchy. The circuit can"t be retriggered faster than the RC time.

Leave Comment

characters left:

New Circuits