[SOLVED] 555 long trigger time with one output cycle

[John150]

Hi,

I'm using a 555 timer to set the output hi for a short period of time and then back low.
The problem: if the trigger low signal its shorter that the output toggling time the circuit works fine.
If the trigger is longer that the output time, the output will stay hi for the hole trigger time (the RC will recharge).
It is any work around for fix this? For a toggling trigger signal no mater the time of the trigger, it is possible to have only one output toggle?

Regards J.

 

[Audioguru]

The datasheet for a 555 says, " The trigger input voltage must return to be high at least 10us before the end of the timing interval".
Then you must capacitive-couple the trigger pulse to pin 2 so that the trigger pulse duration is shorter than the timer output pulse duration.
This Applications Note shows how to do it: