555 output = Vcc for 2nd 555

[MrDEB]

Have seen this done before and feel it's wrong as a 555 will not operate properly.
also will the 555 output drive a second 555??
Model Railway Level Crossing Lights Project
the output of the second 555 provides power for the third 555
am I right in my thinking or just half cocked??

 

[MrDEB]

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

 

[kchriste]

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.

 

[MrDEB]

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.
**broken link removed**

 

[kchriste]

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.