555 Timer Circuit Short pulse Help

Thread Starter

Michael Knight

Joined Nov 5, 2015
90
Connect pin 4 to pin 8, and its perfect.
OK, I tested it out and it seems to work pretty good (Video Uploading) so I'll post that here ASAP.
But I did notice that as soon as I plug in my power supply I get the short pulse right away, not sure if there is a workaround to prevent that?
I also noticed that if one switch is latched then the switches will NOT send a pulse in the off position. Not sure if that can be fixed?

Also I'm guessing I would need a transistor setup like this for each rocker switch?
A little fuzzy on how I would continue the scenario for each switch so a little extra help there would be greatly appreciated lol I'm so "needy" ;)
 
Last edited:

Dodgydave

Joined Jun 22, 2012
8,590
To prevent power up pulse, you will need a 1 meg resistor and 1uF capacitor on pin 4,resistor to pin 8, cap to pin 1, this will hold pin 4 low for about a second.
 

Thread Starter

Michael Knight

Joined Nov 5, 2015
90
To prevent power up pulse, you will need a 1 meg resistor and 1uF capacitor on pin 4,resistor to pin 8, cap to pin 1, this will hold pin 4 low for about a second.
Hmmm I don't have a cap on pin one?
Do you mean I place a 1M resistor and 1uF cap between pins 4 & 8?
What size cap on pin 1?
 

Thread Starter

Michael Knight

Joined Nov 5, 2015
90
OK this is not updated after your change suggestions but you get to see the progress. I'll do another video with the changes Dodgydave suggested :D
 

Thread Starter

Michael Knight

Joined Nov 5, 2015
90
Ok is the timer giving a pulse out on power up or the dtmf chip,?

Try increasing the capacitor to 2uf (microfarads)
I didn't have a 2uF cap the next size up I had was a 10uF, it still does it with a 10uF in there.

Its giving a pulse from the 555 timer on power up.
 

Dodgydave

Joined Jun 22, 2012
8,590
Impossible if pin 4 is held low the timer cant give a positive pulse out, think you have wired pin 4 up wrong.

Try shorting pin 4 to pin one, then power up, it should NOT give a pulse out
 

Thread Starter

Michael Knight

Joined Nov 5, 2015
90
Impossible if pin 4 is held low the timer cant give a positive pulse out, think you have wired pin 4 up wrong.

Try shorting pin 4 to pin one, then power up, it should NOT give a pulse out
Should 8 & 4 be connected directly?
Other wise I have it connected exactly like it my diagram.
 

Dodgydave

Joined Jun 22, 2012
8,590
No, pin 8 is positive supply, pin 4 goes to to the resistor and capacitor like in post #66,
Use a 1 mega ohm resistor and 1micro farad capacitor and the power up delay will be Approx 1second, if its not long enough use a 2.2 microfarads.
 
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