Author Topic: Triggering a 555 through a cap  (Read 742 times)

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Offline QmavamTopic starter

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Triggering a 555 through a cap
« on: February 24, 2020, 05:26:08 pm »
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
« Last Edit: February 24, 2020, 05:29:20 pm by Qmavam »
 

Offline TerminalJack505

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Re: Triggering a 555 through a cap
« Reply #1 on: February 24, 2020, 11:14:41 pm »
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.
« Last Edit: February 25, 2020, 12:57:08 am by TerminalJack505 »
 

Offline TerminalJack505

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Re: Triggering a 555 through a cap
« Reply #2 on: February 25, 2020, 03:41:24 am »
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.
 

Offline Jwillis

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Re: Triggering a 555 through a cap
« Reply #3 on: February 25, 2020, 08:05:37 am »
Try this revision of your circuit.
 


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