I need to make a signal from an IR sensor to last at least half a second. The original signal may last very little so I need to make it longer. What kind of IC/circuit do I need to build?

 

Monostable multivibrator. I'm 100% certain someone will suggest a 555.

Benta.

 

Even with transistors or a very small micro...

The key expresion for a search is "pulse stretcher".

 

I'm 100% certain someone will suggest a 555.

If you can't do it with a '555 it's not worth doing

 

The original signal may last very little so I need to make it longer.

the answer depends on what you meant by "long".

 

If you can't do it with a '555 it's not worth doing

Or PVC pipe!

 

If you can't do it with a '555 it's not worth doing

That's the best post I've read in a long time. My stomach muscles still hurt from laughing. However, I'm still waiting for the suggestion that a 555 is the ideal gate driver for a 300 A IGBT. But it will come one day...

 

I need to make a signal from an IR sensor to last at least half a second. ?

Why? There are hundreds of pulse and timer circuits. A few more details will help narrow the choices.
What is your application?
What is the output pulse used for?
What voltage does it need to be?
How much current must it source or sink?
etc.

ak