This application of the well-known Type 555 timer
is intended for model railway enthusiasts wishing to construct a
two-lamp flashing beacon with a
minimum of components.
With reference to the circuit diagram, the number
of LEDs need not be restricted to two: several may
be connected in parallel to achieve a higher light
intensity, but a total current consumption of
200 mA should not be exceeded to prevent the
destruction of the output stages in the 555. Each
LED added should have its own current limiting resistor, similar to D1-Ra or D2-R4.
The flashing rate is defined with C1. The stated
value of this component is likely to be optimum for
applications in model railways. The supply voltage
for the circuit is not critical, but should remain
within the range from 5 to 10 V With two LEDs
fitted and a 5 V supply, the flashing circuit should
consume less than 50 mA. The intensity of the
LEDs can be adapted to individual preference by
changing Ra and R4, but too low resistance values
should be avoided to prevent the destruction of the
LEDs.