CIRCUIT OPERATION
The
weight of the train operates push button switch positioned on the track. The
trigger push button switch starts the sequence by switching on the amber light,
a few seconds later the two red lights lit ON. When the train has passed the
level crossing it operates the cancel push button switch which switches OFF the
red lights and switches the green lights ON to allow cars to cross the railway until
the next train arrives.
The circuit contain two 555 timer
1.
Monostable
2.
Bistable
This
project uses a 555 monostable
circuit to switch on the amber LED for a few seconds. When this switches off it
triggers a 555 bistable
circuit.
1.
Monostable
A
monostable circuit produces a single output pulse when triggered. It is called
a monostable because it is stable in just one state: 'output low'. The
'output high' state is temporary.
Monostable operation
Monostable
mode: in this mode, the 555 functions as a "one-shot" pulse
generator. Applications include timers, missing pulse detection, bounce free
switches, and touch switches, frequency divider, capacitance measurement,
pulse-width modulation (PWM) and so on.
2. Bistable (flip-flop) - a memory circuit
Bistable
mode or Schmitt trigger: the 555 can operate as a flip-flop, if the DIS pin is
not connected and no capacitor is used. Uses include bounce-free latched
switches
The
circuit is called a bistable because it is stable in two states: output high
and output low. It is also known as a 'flip-flop'.
Model railway level crossing lights is the circuit which designed to prevent cars from accident when the train crossing the road.
This circuit allows car to cross the railway when green LED
lights ON. When the train is coming it trigger the circuit through push button
that placed a certain distance before the crossing level, amber LED lights ON
for a few seconds and red LED lights ON that predicts the train is crossing.
After crossing railway, the train cancel
through push button, red LED lights OFF and green LED lights ON that allow cars to cross the railway until the next
train arrives.
