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555 output = Vcc for 2nd 555

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MrDEB

Well-Known Member
not sure if this is cosiure

usng the reset pin to trigger an astable 555 timer.
tried different things but this looks like it works
am using the LOAD componet as a pulse input to reset. taking reset high which starts the astable timer.
works better than the link I posted in my first post
 

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kchriste

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the output of the second 555 provides power for the third 555
Nothing really wrong with that since the 555 can source 200ma which is plenty for the 3rd 555.
Advantages:
Power savings when the 3rd 555 is turned "Off" by the 2nd.
Simple method of ensuring both red LEDs are off when the train leaves the crossing area.
Disadvantage:
Slightly lower output voltage on pin 3 of 3rd 555. Not that it matters in that circuit.
 
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MrDEB

Well-Known Member
one slight problem

when a 555 is powered up the internal circuitry has to do its thing thus leading to weird behavior
in this link it talks about what happens when a 555 is powered on and a cure for it.
LM555 Timer Circuits
 

kchriste

New Member
Forum Supporter
That only really applies to monostable 555 circuits. The astable LED flasher in the model railroad crossing recovers from the power up sequence in the first LED flash time. All that happens is that the first flash is a little longer than subsequent ones because the timing cap is at 0Vcc as opposed to 1/3Vcc during a normal flash cycle.
 
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