Monostable multivibrators
Here's a version made with a 555 multivibrator ( please scroll down the page until you find it )
A monostable made with an operational amplifier ( scroll as above to find it )
different tecnologies providing us monostable multivibrators.
After following the links given and reading the contents suggested.
Compare these devices( try to figure out why you could prefer one or the other depending on the application. )
Design and simulate a monostable multivibrator for each type. The two must have an active output of 300ms.