Mono stable 555 circuit

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b1mmuo27

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I think from my previous post that the circuit I need may be a mono stable 555 timer circuit. I have a question regarding the circuit. If my trigger is +12vdc for 1 second or less would my output from the circuit be the +12vdc for 5 seconds?
 
Thanks, Ive seen that page but that doesn't answer my question. My knowledge in electronics is limited that's why I asked this question.
 
Did you not see the R-C calculator, just plug in the values and you get the time constant. The output is allays the same amplitude as VCC.
 
Rolf said:
The output is always the same amplitude as VCC.
No. The amplitude of the output of an ordinary 555 is about 1.2V to 2.5V less than the supply, or 0.1V up to 2.5V above ground, depending on its output current.
A Cmos 555 has an output at the supply voltage or at ground if it dosen't have a load.
 
But is it not close enough for government work. LOL
Thanks, I am getting a little rusty.

Rolf
 
Rolf said:
But is it not close enough for government work. LOL
Whose government?
The output voltage of an ordinary 555 doesn't go high enough to turn off a PNP transistor.
 
b1mmuo27 said:
I think from my previous post that the circuit I need may be a mono stable 555 timer circuit. I have a question regarding the circuit. If my trigger is +12vdc for 1 second or less would my output from the circuit be the +12vdc for 5 seconds?
Well post it in the other thread, don't make a new one, as it makes it harder for people like me who're trying to help you!
 
A 555 monostable needs a negative-going signal on pin 2 and the voltage at pin 2 must return to being high again before the timeout.
Yes, the output will be high (about +10.5V) during the timeout.
 
You need a DC blocking capacitor pullup resistor and transistor inverter on the input if the pulse lasts longer than the delay and is positive.
 
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