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Circuit Help

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MrDEB

Well-Known Member
prety simple circuit

the first 555 is a one shot timer. It outputs one pulse from pin 3 to pin 2 of second 555 (trigger input)
the second 555 is an bi-stable timer. It controls the third timer set up as an astable timer (outputs a train of pulses instead of just one pulse.)
the output of the second controls the third timer.
this circuit can be reconfigured so only one 556 (2-555"s in one package) can be utilized.
Haven't figured out why they put the bi-stable (acts like a toggle switch) in the mix.
look at this site as it explains all of this
LM555 Timer Circuits
 

MikeMl

Well-Known Member
Most Helpful Member
What do you need. The article seems to be complete.
 

MrDEB

Well-Known Member
Noticed one major problem

with that posted link - the train can only go in one direction for the circuit to work.
working on an idea that detects model train coming from either direction, using only 2 IC's or using one micro-controller.
also using reed switches is not as reliable as a photo-transistor arrangement.
will get back to you if your interested.
 

BrownOut

Banned
That's a fun project! I always wanted to make one of these. It just never bubbled to the top of my project list :)
 

MrDEB

Well-Known Member
taking a second look at schematic

the third 555 is being powered by the second 555 output-I don't think this is a good idea as the output won't drive it or it may cause eratic behavior
at least that's my take on this schematic as well as the train can only go one direction for it to work
 

mneary

New Member
Another issue to tackle is that the signal will cancel as soon as the front of the train passes the cancel switch, even if the back of the train is still on the crossing.
 

MrDEB

Well-Known Member
working on that

planning on using a D flip flop.
have it almost configured by using a divide by two 4013 circuit.
train starts the one shot then the one shot triggers a D flip flop hen when train finishes passing over last sensor the 4013 resets for next train, regardless of direction of travel.
this would be so easy using a PIC but configuring using cmos or TTL is kinda fun.
 

MrDEB

Well-Known Member
I think I have it.

this circuit detects a train coming from either direction
at least it works in LT spice
cmos could be used instead of TTL and a 556 instead of two - 555's
 

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Silly Britts

please can any one help in internal working of the circuit available in this site Model Railway Level Crossing Lights Project

I'VE SEEN THIS BEFORE!!! When I made my circuit it was not working properly so I switched to a different circuit that uses only one 555 timer as a sinking sourcing circuit.

Don't worry if the circuit doesn't work, it's British, and the Britts do things slightly differently than us Americans.https://static.electro-tech-online.com/images/icons/icon12.gif
 
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