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FLASHING FOR A CROSSING

FLASHING FOR A CROSSING

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  IDEA ELECTRONIC PROJECT

WHAT'S THE POINT?
This turn signal light is not for railways, they do not need it. On the other hand, if you are an enlightened amateur of model railway, you absolutely need this accessory. The flashing of the level crossing will be achieved by an LED which normally has no inertia. Now the incandescent bulbs used in practice have one, which we simulated here ...


THE SCHEME
If you do not know, there is a well known integrated circuit called NE 555 that is a small oscillator all by itself. It is Ch. Surrounded by some components, carefully selected values, it generates a square wave at 70 periods per minute, the cadence SNCF. The square signal is shaped by a delay circuit which slows up and down the current in the LEDs of the crossing (there are two diodes, one on each side of the crossing). The capacitors C2, C3, C4 to create the inertia, their value can be changed if you find that realism is not assured. The plant is associated here with three circuits that will equip three level crossings. Since the switching is carried out before the capacitor and not directly on the LEDs (which would have been simpler), the inertia at switching on and off will be beneficial. Moreover, the control unit can be used for a greater number of PNs, it will suffice for this to repeat the circuit RC + transistors and diodes. Finally, the 555 can output a lot of current, which allows to associate the power station with a hundred crossings ...


PRODUCTION
The printed circuit is provided for three level crossings. No particular problem for the realization: if you have already succeeded in installing a LED in the fire of the PN, it is that you are skilled enough to wire the assembly! Observe the direction of the LED, tantalum and chemical capacitors. The control contact will be NO; It closes during the entire closing time of the passage. Two LEDs are connected in series. No tuning to do, no adjustment either. The power supply can be from 6 to 12 V, the transistors are mounted as a current generator, and the series resistance can be the same regardless of the supply voltage.

LIST OF COMPONENTS
Resistors 1/4 W, 5%
R1: 15 kR
R2: 820kR
R3, R4, R5, R6, R7, R8:
R9, R10, R11: 100R
R12, R13, R14: 33kR
R15, R16, R17: 220 R

Capacitors
C1: chemical condenser 1 mF 16V
C2, C3, C4: tantalum capacitor 4.7 MF 6.3 V

Semiconductors
T1, T2, T3: BC transistors 548, 108, etc. NPN Si
CI1: Integrated Circuit NE 555
LED diodes, D1 to D6, red miniature diodes

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