Electronics > Beginners

Triggering a 555 through a cap

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Qmavam:
I'm try to help the guy with the LDR triggering a 555.
I'm slowly walking him through it and now just triggering it with a wire momentarily to grd, to pull Pin 2 low, through a capacitor.
 But it won't trigger.
Here's the circuit, what is needed to make the circuit trigger properly.

 
                            Thanks, Mikek

TerminalJack505:
It should work.  The problem may be that it is powering-up in the triggered state.

Also, the values used for the trigger pulse are likely too large.  If you don't have an oscilloscope then you should grab a simulator so that you can get a better idea about what the circuit is doing and how the component values effect the circuit's behavior.

TerminalJack505:
This circuit here should do what you are wanting to do.  It will avoid triggering on power-on. 

The only thing you will need to do is change the values of R1 and C1.

Jwillis:
Try this revision of your circuit.

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