More Model Railway
This circuit flashes two
red LEDs for a model railway crossing.
clever circuit using two 555's to produce a set of traffic lights
for a model layout.
The animation shows the lighting sequence and this follows the
Australian-standard. The red LED has an equal on-off period and when
it is off, the first 555 delivers power to the second 555. This
illuminates the Green LED and then the second 555 changes state to
turn off the Green LED and turn on the Orange LED for a short period
of time before the first 555 changes state to turn off the second
555 and turn on the red LED. A supply voltage of 9v to 12v is needed
because the second 555 receives a supply of about 2v less than rail.
This circuit also shows how to connect LEDs high and low to a 555
and also turn off the 555 by controlling the supply to pin 8.
Connecting the LEDs high and low to pin 3 will not work and since
pin 7 is in phase with pin 3, it can be used to advantage in this
Here is a
further description of how the circuit works:
Both 555's are wired as oscillators in astable mode and will
oscillate ALL THE TIME when they are turned ON. But the second 555
is not turned on all the time!
The first 555 turns on and the 100u is not charged. This makes
output pin 3 HIGH and the red LED is not illuminated. However the
output feeds the second 555 and it turns on.
Output pin 3 of the second 555 turns on the green LED and the
second 100u charges to 2/3 rail voltage and causes the 555 to change
states. The green LED goes off and the orange LED turns on.
The second 100u starts to discharge, but the first 100u is charging
via a 100k and after the orange LED has been on for a short period
of time, the first 555 changes state and pin 3 goes LOW.
This turns on the red LED and turns off the second 555.
The first 100u starts to discharge via the 100k and eventually it
changes state to start the cycle again.
The secret of the timing is the long cycle-time of the first 555 due
to the 100k and the short cycle due to the 47k on the second 555.
|4 WAY TRAFFIC
circuit produces traffic
lights for a "4-way" intersection. The seemingly complex wiring to
illuminate the lights is shown to be very simple.
Here is a circuit that will
convert any clock mechanism into Model Railway Time.
For those who enjoy model railways, the ultimate is to have a
fast clock to match the scale of the layout. This circuit will
appear to "make time fly" by turning the seconds hand once every
6 seconds. The timing can be adjusted by changing the 47k. The
electronics in the clock is disconnected from the coil and the
circuit drives the coil directly. The circuit takes a lot more
current than the original clock (1,000 times more) but this is
one way to do the job without a sophisticated chip.
|REVERSING A MOTOR-4
(see 1, 2, 3 in 200 Transistor Circuits)
In this example the power is
applied via the start switch and the train moves to the away limit
switch and stops. The 555 creates a delay of 1 minute and the train
moves to the home limit and stops. Turn the power on-off to restart