hi all
something thats always puzzled me, why does the 555 trigger on a negative going signal rather than the more logical, to me anyway, a positive going one.

i know its easy to work round,
thank you
dougal

 

Because when you use it as an oscillator, it uses the dropping voltage during the discharge of its RC network to trigger itself.

 

thanks mike
i knew there would be reason

i suppose before it was used for anything and everything it is an oscillator.