Help. Transistor info.

[pedro_penduko]

Gurus,

Can someone explain how the transistor works on the image.

 

[crutschow]

It would appear to be some sort of common-base level translator. 0V at the emitter input (transistor off) gives 5V at the collector output. A sufficiently negative voltage at the emitter input (transistor on) gives 0V (or a slightly negative voltage) at the collector output.

 

[pedro_penduko]

Thanks for that info. Is there any much simpler circuit that is equivalent to that? I need to get a pulse (+5v input to digital pin) from a negative signal from the above sample.

Or is it possible, get an +pulse from negative signal and +pulse from positive signal?