LM7555 Monostable Trigger

[Xenos]

Hello,

When configuring an LM7555 in monostable mode, as shown on the schematic, is there a method to make the pressing of the button a momentary event, no matter how long the button is held down? In the circuit shown here, the LED will stay illuminated as long as the switch is closed. Only after releasing the button will the timer begin. In my project, in lieu of the button, I have an IR break-beam that triggers a LM393, which in turn energizes a transistor that triggers the LM7555. The issue is that as long as the beam is blocked, the output of the LM7555 is active.

An analogy would be how some doorbells ding when you hold the button, then dong when you release it. I would like to make it so when the button is pressed and held, the doorbell does a full ding-dong cycle. Essentially, the button press automatically resets the trigger, until it is pressed again.

Thanks in advance!

[jpanhalt]

Yes, use a capacitor in the trigger circuit.  Example attached.

EDIT:
And another example of the same approach from the Paisley site (attachment 2).

[Xenos]

Thank you very much!