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A Beginner's Guide to Circuits by Øyvind Nydal Dahl

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6THE RAILROAD CROSSING LIGHT

THIS CIRCUIT FLASHES TWO LEDS IN AN ALTERNATING PATTERN.

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THE CIRCUIT DIAGRAM

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THE PARTS LIST

PART

VALUE

DESCRIPTION

R1, R4

470 Ω

Standard resistor

R2, R3

47 kΩ

Standard resistor

Q1, Q2

BC547

Any general-purpose NPN transistor

C1, C2

10 μF

Polarized capacitor

L1, L2

 

Standard-output light-emitting diode

ABOUT THE CIRCUIT

This circuit makes two LEDs flash in an alternating pattern. You can use it for a model railroad crossing, for example, or for eyes on a toy robot.

This is a classic circuit called ...

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