6THE RAILROAD CROSSING LIGHT

THIS CIRCUIT FLASHES TWO LEDS IN AN ALTERNATING PATTERN.

image

THE CIRCUIT DIAGRAM

image

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 ...

Get A Beginner's Guide to Circuits now with O’Reilly online learning.

O’Reilly members experience live online training, plus books, videos, and digital content from 200+ publishers.